From 263267c5ad013d314574fcd9bc6a744699e226c5 Mon Sep 17 00:00:00 2001
From: Joe Testa <jtesta@positronsecurity.com>
Date: Tue, 25 Apr 2023 09:17:32 -0400
Subject: [PATCH] Added support for mixed host key/CA key types (i.e.: RSA host
 keys signed by ED25519 CAs) (#120).

---
 README.md                                     |   1 +
 docker_test.sh                                |   4 +-
 src/ssh_audit/gextest.py                      |  18 +-
 src/ssh_audit/hostkeytest.py                  | 100 +++++---
 src/ssh_audit/kexdh.py                        | 242 ++++++++++--------
 src/ssh_audit/policy.py                       | 159 ++++++++----
 src/ssh_audit/ssh2_kex.py                     |  40 ++-
 src/ssh_audit/ssh_audit.py                    |  96 ++++---
 src/ssh_audit/ssh_socket.py                   |   2 +-
 .../openssh_5.6p1_custom_policy_test10.json   |   4 +-
 .../openssh_5.6p1_custom_policy_test10.txt    |  19 +-
 .../openssh_5.6p1_custom_policy_test7.txt     |  15 ++
 .../openssh_5.6p1_custom_policy_test8.json    |   2 +-
 .../openssh_5.6p1_custom_policy_test8.txt     |  17 +-
 .../openssh_5.6p1_custom_policy_test9.json    |   2 +-
 .../openssh_5.6p1_custom_policy_test9.txt     |  17 +-
 .../expected_results/openssh_5.6p1_test2.json |   1 +
 .../expected_results/openssh_5.6p1_test2.txt  |   9 +-
 .../expected_results/openssh_5.6p1_test3.json |   1 +
 .../expected_results/openssh_5.6p1_test3.txt  |   8 +-
 .../expected_results/openssh_5.6p1_test4.json |   1 +
 .../expected_results/openssh_5.6p1_test4.txt  |   8 +-
 .../expected_results/openssh_5.6p1_test5.json |   1 +
 .../expected_results/openssh_5.6p1_test5.txt  |   6 +-
 .../openssh_8.0p1_custom_policy_test11.txt    |   9 +
 .../openssh_8.0p1_custom_policy_test12.json   |   6 +-
 .../openssh_8.0p1_custom_policy_test12.txt    |  15 +-
 .../openssh_8.0p1_custom_policy_test13.txt    |  12 +
 .../openssh_8.0p1_custom_policy_test14.txt    |  12 +
 .../expected_results/openssh_8.0p1_test2.json |   4 +-
 .../expected_results/openssh_8.0p1_test2.txt  |   2 +-
 test/test_build_struct.py                     |  21 +-
 test/test_policy.py                           |   4 +-
 test/test_ssh2.py                             |   6 +-
 34 files changed, 556 insertions(+), 308 deletions(-)

diff --git a/README.md b/README.md
index 18f611b..02d1f29 100644
--- a/README.md
+++ b/README.md
@@ -187,6 +187,7 @@ For convenience, a web front-end on top of the command-line tool is available at
  - Snap packages now print more user-friendly error messages when permission errors are encountered.
  - JSON 'target' field now always includes port number; credit [tomatohater1337](https://github.com/tomatohater1337).
  - JSON output now includes recommendations and CVE data.
+ - Mixed host key/CA key types (i.e.: RSA host keys signed with ED25519 CAs, etc.) are now properly handled.
  - Warnings are now printed for 2048-bit moduli.
  - SHA-1 algorithms now cause failures.
  - CBC mode ciphers are now warnings instead of failures.
diff --git a/docker_test.sh b/docker_test.sh
index b619368..d7c71d4 100755
--- a/docker_test.sh
+++ b/docker_test.sh
@@ -616,8 +616,8 @@ run_policy_test() {
         exit 1
     fi
 
-    #echo "Running: ./ssh-audit.py -P \"${policy_path}\" -jj localhost:2222 > ${test_result_json}"
-    ./ssh-audit.py -P "${policy_path}" -jj localhost:2222 > "${test_result_json}"
+    #echo "Running: ./ssh-audit.py -P \"${policy_path}\" -jj localhost:2222 > ${test_result_json} 2> /dev/null"
+    ./ssh-audit.py -P "${policy_path}" -jj localhost:2222 > "${test_result_json}" 2> /dev/null
     actual_exit_code=$?
     if [[ ${actual_exit_code} != "${expected_exit_code}" ]]; then
         echo -e "${test_name} ${REDB}FAILED${CLR} (expected exit code: ${expected_exit_code}; actual exit code: ${actual_exit_code}\n"
diff --git a/src/ssh_audit/gextest.py b/src/ssh_audit/gextest.py
index 3eb1bf7..97bafd4 100644
--- a/src/ssh_audit/gextest.py
+++ b/src/ssh_audit/gextest.py
@@ -27,7 +27,7 @@ import traceback
 from typing import Dict, List, Set, Sequence, Tuple, Iterable  # noqa: F401
 from typing import Callable, Optional, Union, Any  # noqa: F401
 
-from ssh_audit.kexdh import KexGroupExchange_SHA1, KexGroupExchange_SHA256
+from ssh_audit.kexdh import KexDHException, KexGroupExchange_SHA1, KexGroupExchange_SHA256
 from ssh_audit.ssh2_kexdb import SSH2_KexDB
 from ssh_audit.ssh2_kex import SSH2_Kex
 from ssh_audit.ssh_socket import SSH_Socket
@@ -63,8 +63,8 @@ class GEXTest:
         try:
             # Parse the server's KEX.
             _, payload = s.read_packet(2)
-            SSH2_Kex.parse(payload)
-        except Exception:
+            SSH2_Kex.parse(out, payload)
+        except KexDHException:
             out.v("Failed to parse server's kex.  Stack trace:\n%s" % str(traceback.format_exc()), write_now=True)
             return False
 
@@ -98,7 +98,7 @@ class GEXTest:
             if gex_alg not in kex.kex_algorithms:
                 out.d('Server does not support the algorithm "' + gex_alg + '".', write_now=True)
             else:
-                kex_group = kex_group_class()
+                kex_group = kex_group_class(out)
                 out.d('Preparing to perform DH group exchange using ' + gex_alg + ' with min, pref and max modulus sizes of ' + str(bits_min) + ' bits, ' + str(bits_pref) + ' bits and ' + str(bits_max) + ' bits...', write_now=True)
 
                 # It has been observed that reconnecting to some SSH servers
@@ -115,7 +115,7 @@ class GEXTest:
                     kex_group.recv_reply(s, False)
                     modulus_size_returned = kex_group.get_dh_modulus_size()
                     out.d('Modulus size returned by server: ' + str(modulus_size_returned) + ' bits', write_now=True)
-                except Exception:
+                except KexDHException:
                     out.d('[exception] ' + str(traceback.format_exc()), write_now=True)
                 finally:
                     # The server is in a state that is not re-testable,
@@ -155,7 +155,7 @@ class GEXTest:
                 if GEXTest.reconnect(out, s, kex, gex_alg) is False:
                     break
 
-                kex_group = kex_group_class()
+                kex_group = kex_group_class(out)
                 smallest_modulus = -1
 
                 # First try a range of weak sizes.
@@ -169,7 +169,7 @@ class GEXTest:
                     smallest_modulus = kex_group.get_dh_modulus_size()
                     out.d('Modulus size returned by server: ' + str(smallest_modulus) + ' bits', write_now=True)
 
-                except Exception:
+                except KexDHException:
                     out.d('[exception] ' + str(traceback.format_exc()), write_now=True)
                 finally:
                     s.close()
@@ -194,8 +194,8 @@ class GEXTest:
                         kex_group.recv_reply(s, False)
                         smallest_modulus = kex_group.get_dh_modulus_size()
                         out.d('Modulus size returned by server: ' + str(smallest_modulus) + ' bits', write_now=True)
-                    except Exception:
-                        out.d('[exception] ' + str(traceback.format_exc()), write_now=True)
+                    except KexDHException as e:
+                        out.d('Exception when testing DH group exchange ' + gex_alg + ' with modulus size ' + str(bits) + '.  (Hint: this is probably normal since the server does not support this modulus size.): ' + str(e), write_now=True)
                     finally:
                         # The server is in a state that is not re-testable,
                         # so there's nothing else to do with this open
diff --git a/src/ssh_audit/hostkeytest.py b/src/ssh_audit/hostkeytest.py
index 26aa48d..400a674 100644
--- a/src/ssh_audit/hostkeytest.py
+++ b/src/ssh_audit/hostkeytest.py
@@ -28,7 +28,7 @@ from typing import Callable, Optional, Union, Any  # noqa: F401
 
 import traceback
 
-from ssh_audit.kexdh import KexDH, KexGroup1, KexGroup14_SHA1, KexGroup14_SHA256, KexCurve25519_SHA256, KexGroup16_SHA512, KexGroup18_SHA512, KexGroupExchange_SHA1, KexGroupExchange_SHA256, KexNISTP256, KexNISTP384, KexNISTP521
+from ssh_audit.kexdh import KexDH, KexDHException, KexGroup1, KexGroup14_SHA1, KexGroup14_SHA256, KexCurve25519_SHA256, KexGroup16_SHA512, KexGroup18_SHA512, KexGroupExchange_SHA1, KexGroupExchange_SHA256, KexNISTP256, KexNISTP384, KexNISTP521
 from ssh_audit.ssh2_kex import SSH2_Kex
 from ssh_audit.ssh2_kexdb import SSH2_KexDB
 from ssh_audit.ssh_socket import SSH_Socket
@@ -55,6 +55,7 @@ class HostKeyTest:
     }
 
     TWO2K_MODULUS_WARNING = '2048-bit modulus only provides 112-bits of symmetric strength'
+    SMALL_ECC_MODULUS_WARNING = '224-bit ECC modulus only provides 112-bits of symmetric strength'
 
 
     @staticmethod
@@ -82,7 +83,7 @@ class HostKeyTest:
         for server_kex_alg in server_kex.kex_algorithms:
             if server_kex_alg in KEX_TO_DHGROUP:
                 kex_str = server_kex_alg
-                kex_group = KEX_TO_DHGROUP[kex_str]()
+                kex_group = KEX_TO_DHGROUP[kex_str](out)
                 break
 
         if kex_str is not None and kex_group is not None:
@@ -110,7 +111,6 @@ class HostKeyTest:
                 out.d('Preparing to obtain ' + host_key_type + ' host key...', write_now=True)
 
                 cert = host_key_types[host_key_type]['cert']
-                variable_key_len = host_key_types[host_key_type]['variable_key_len']
 
                 # If the connection is closed, re-open it and get the kex again.
                 if not s.is_connected():
@@ -131,7 +131,7 @@ class HostKeyTest:
                     try:
                         # Parse the server's KEX.
                         _, payload = s.read_packet()
-                        SSH2_Kex.parse(payload)
+                        SSH2_Kex.parse(out, payload)
                     except Exception:
                         out.v("Failed to parse server's kex.  Stack trace:\n%s" % str(traceback.format_exc()), write_now=True)
                         return
@@ -139,15 +139,29 @@ class HostKeyTest:
                 # Do the initial DH exchange.  The server responds back
                 # with the host key and its length.  Bingo.  We also get back the host key fingerprint.
                 kex_group.send_init(s)
+                raw_hostkey_bytes = b''
                 try:
-                    host_key = kex_group.recv_reply(s, variable_key_len)
-                    if host_key is not None:
-                        server_kex.set_host_key(host_key_type, host_key)
-                except Exception:
-                    pass
+                    kex_reply = kex_group.recv_reply(s)
+                    raw_hostkey_bytes = kex_reply if kex_reply is not None else b''
+                except KexDHException:
+                    out.v("Failed to parse server's host key.  Stack trace:\n%s" % str(traceback.format_exc()), write_now=True)
+
+                    # Since parsing this host key failed, there's nothing more to do but close the socket and move on to the next host key type.
+                    s.close()
+                    continue
 
                 hostkey_modulus_size = kex_group.get_hostkey_size()
+                ca_key_type = kex_group.get_ca_type()
                 ca_modulus_size = kex_group.get_ca_size()
+                out.d("Hostkey type: [%s]; hostkey size: %u; CA type: [%s]; CA modulus size: %u" % (host_key_type, hostkey_modulus_size, ca_key_type, ca_modulus_size), write_now=True)
+
+                # Record all the host key info.
+                server_kex.set_host_key(host_key_type, raw_hostkey_bytes, hostkey_modulus_size, ca_key_type, ca_modulus_size)
+
+                # Set the hostkey size for all RSA key types since 'ssh-rsa', 'rsa-sha2-256', etc. are all using the same host key.  Note, however, that this may change in the future.
+                if cert is False and host_key_type in HostKeyTest.RSA_FAMILY:
+                    for rsa_type in HostKeyTest.RSA_FAMILY:
+                        server_kex.set_host_key(rsa_type, raw_hostkey_bytes, hostkey_modulus_size, ca_key_type, ca_modulus_size)
 
                 # Close the socket, as the connection has
                 # been put in a state that later tests can't use.
@@ -155,43 +169,53 @@ class HostKeyTest:
 
                 # If the host key modulus or CA modulus was successfully parsed, check to see that its a safe size.
                 if hostkey_modulus_size > 0 or ca_modulus_size > 0:
-                    # Set the hostkey size for all RSA key types since 'ssh-rsa',
-                    # 'rsa-sha2-256', etc. are all using the same host key.
-                    # Note, however, that this may change in the future.
-                    if cert is False and host_key_type in HostKeyTest.RSA_FAMILY:
-                        for rsa_type in HostKeyTest.RSA_FAMILY:
-                            server_kex.set_rsa_key_size(rsa_type, hostkey_modulus_size)
-                    elif cert is True:
-                        server_kex.set_rsa_key_size(host_key_type, hostkey_modulus_size, ca_modulus_size)
+                    # The minimum good modulus size for RSA host keys is 3072.  However, since ECC cryptosystems are fundamentally different, the minimum good is 256.
+                    hostkey_min_good = cakey_min_good = 3072
+                    hostkey_min_warn = cakey_min_warn = 2048
+                    hostkey_warn_str = cakey_warn_str = HostKeyTest.TWO2K_MODULUS_WARNING
+                    if host_key_type.startswith('ssh-ed25519') or host_key_type.startswith('ecdsa-sha2-nistp'):
+                        hostkey_min_good = 256
+                        hostkey_min_warn = 224
+                        hostkey_warn_str = HostKeyTest.SMALL_ECC_MODULUS_WARNING
+                    if ca_key_type.startswith('ssh-ed25519') or host_key_type.startswith('ecdsa-sha2-nistp'):
+                        cakey_min_good = 256
+                        cakey_min_warn = 224
+                        cakey_warn_str = HostKeyTest.SMALL_ECC_MODULUS_WARNING
 
                     # Keys smaller than 2048 result in a failure.  Keys smaller 3072 result in a warning.  Update the database accordingly.
-                    if (cert is False) and (hostkey_modulus_size < 3072):
-                        for rsa_type in HostKeyTest.RSA_FAMILY:
-                            alg_list = SSH2_KexDB.ALGORITHMS['key'][rsa_type]
-
-                            # Ensure that failure & warning lists exist.
-                            while len(alg_list) < 3:
-                                alg_list.append([])
-
-                            # If the key is under 2048, add to the failure list.
-                            if hostkey_modulus_size < 2048:
-                                alg_list[1].append('using small %d-bit modulus' % hostkey_modulus_size)
-                            elif HostKeyTest.TWO2K_MODULUS_WARNING not in alg_list[2]:  # Issue a warning about 2048-bit moduli.
-                                alg_list[2].append(HostKeyTest.TWO2K_MODULUS_WARNING)
-
-                    elif (cert is True) and ((hostkey_modulus_size < 3072) or (ca_modulus_size > 0 and ca_modulus_size < 3072)):  # pylint: disable=chained-comparison
+                    if (cert is False) and (hostkey_modulus_size < hostkey_min_good):
                         alg_list = SSH2_KexDB.ALGORITHMS['key'][host_key_type]
-                        min_modulus = min(hostkey_modulus_size, ca_modulus_size)
-                        min_modulus = min_modulus if min_modulus > 0 else max(hostkey_modulus_size, ca_modulus_size)
 
                         # Ensure that failure & warning lists exist.
                         while len(alg_list) < 3:
                             alg_list.append([])
 
-                        if (hostkey_modulus_size < 2048) or (ca_modulus_size > 0 and ca_modulus_size < 2048):  # pylint: disable=chained-comparison
-                            alg_list[1].append('using small %d-bit modulus' % min_modulus)
-                        elif HostKeyTest.TWO2K_MODULUS_WARNING not in alg_list[2]:
-                            alg_list[2].append(HostKeyTest.TWO2K_MODULUS_WARNING)
+                        # If the key is under 2048, add to the failure list.
+                        if hostkey_modulus_size < hostkey_min_warn:
+                            alg_list[1].append('using small %d-bit modulus' % hostkey_modulus_size)
+                        elif hostkey_warn_str not in alg_list[2]:  # Issue a warning about 2048-bit moduli.
+                            alg_list[2].append(hostkey_warn_str)
+
+                    elif (cert is True) and ((hostkey_modulus_size < hostkey_min_good) or (0 < ca_modulus_size < cakey_min_good)):
+                        alg_list = SSH2_KexDB.ALGORITHMS['key'][host_key_type]
+
+                        # Ensure that failure & warning lists exist.
+                        while len(alg_list) < 3:
+                            alg_list.append([])
+
+                        # If the host key is smaller than 2048-bit/224-bit, flag this as a failure.
+                        if hostkey_modulus_size < hostkey_min_warn:
+                            alg_list[1].append('using small %d-bit hostkey modulus' % hostkey_modulus_size)
+                        # Otherwise, this is just a warning.
+                        elif (hostkey_modulus_size < hostkey_min_good) and (hostkey_warn_str not in alg_list[2]):
+                            alg_list[2].append(hostkey_warn_str)
+
+                        # If the CA key is smaller than 2048-bit/224-bit, flag this as a failure.
+                        if 0 < ca_modulus_size < cakey_min_warn:
+                            alg_list[1].append('using small %d-bit CA key modulus' % ca_modulus_size)
+                        # Otherwise, this is just a warning.
+                        elif (0 < ca_modulus_size < cakey_min_good) and (cakey_warn_str not in alg_list[2]):
+                            alg_list[2].append(cakey_warn_str)
 
                 # If this host key type is in the RSA family, then mark them all as parsed (since results in one are valid for them all).
                 if host_key_type in HostKeyTest.RSA_FAMILY:
diff --git a/src/ssh_audit/kexdh.py b/src/ssh_audit/kexdh.py
index 12edc9e..9baab73 100644
--- a/src/ssh_audit/kexdh.py
+++ b/src/ssh_audit/kexdh.py
@@ -1,7 +1,7 @@
 """
    The MIT License (MIT)
 
-   Copyright (C) 2017-2021 Joe Testa (jtesta@positronsecurity.com)
+   Copyright (C) 2017-2023 Joe Testa (jtesta@positronsecurity.com)
    Copyright (C) 2017 Andris Raugulis (moo@arthepsy.eu)
 
    Permission is hereby granted, free of charge, to any person obtaining a copy
@@ -31,6 +31,7 @@ import struct
 from typing import Dict, List, Set, Sequence, Tuple, Iterable  # noqa: F401
 from typing import Callable, Optional, Union, Any  # noqa: F401
 
+from ssh_audit.outputbuffer import OutputBuffer
 from ssh_audit.protocol import Protocol
 from ssh_audit.ssh_socket import SSH_Socket
 
@@ -40,7 +41,8 @@ class KexDHException(Exception):
 
 
 class KexDH:  # pragma: nocover
-    def __init__(self, kex_name: str, hash_alg: str, g: int, p: int) -> None:
+    def __init__(self, out: 'OutputBuffer', kex_name: str, hash_alg: str, g: int, p: int) -> None:
+        self.out = out
         self.__kex_name = kex_name  # pylint: disable=unused-private-member
         self.__hash_alg = hash_alg  # pylint: disable=unused-private-member
         self.__g = 0
@@ -51,10 +53,11 @@ class KexDH:  # pragma: nocover
         self.set_params(g, p)
 
         self.__ed25519_pubkey: Optional[bytes] = None  # pylint: disable=unused-private-member
-        self.__hostkey_type: Optional[bytes] = None
+        self.__hostkey_type = ''
         self.__hostkey_e = 0  # pylint: disable=unused-private-member
         self.__hostkey_n = 0  # pylint: disable=unused-private-member
         self.__hostkey_n_len = 0  # Length of the host key modulus.
+        self.__ca_key_type = ''  # Type of CA key ('ssh-rsa', etc).
         self.__ca_n_len = 0  # Length of the CA key modulus (if hostkey is a cert).
 
     def set_params(self, g: int, p: int) -> None:
@@ -76,6 +79,14 @@ class KexDH:  # pragma: nocover
     # contains the host key, among other things.  Function returns the host
     # key blob (from which the fingerprint can be calculated).
     def recv_reply(self, s: 'SSH_Socket', parse_host_key_size: bool = True) -> Optional[bytes]:
+        # Reset the CA info, in case it was set from a prior invokation.
+        self.__hostkey_type = ''
+        self.__hostkey_e = 0  # pylint: disable=unused-private-member
+        self.__hostkey_n = 0  # pylint: disable=unused-private-member
+        self.__hostkey_n_len = 0
+        self.__ca_key_type = ''
+        self.__ca_n_len = 0
+
         packet_type, payload = s.read_packet(2)
 
         # Skip any & all MSG_DEBUG messages.
@@ -88,23 +99,12 @@ class KexDH:  # pragma: nocover
             # A connection error occurred.  We can't parse anything, so just
             # return.  The host key modulus (and perhaps certificate modulus)
             # will remain at length 0.
+            self.out.d("KexDH.recv_reply(): received packge_type == -1.")
             return None
 
-        hostkey_len = 0  # pylint: disable=unused-variable
-        hostkey_type_len = hostkey_e_len = 0  # pylint: disable=unused-variable
-        key_id_len = principles_len = 0  # pylint: disable=unused-variable
-        critical_options_len = extensions_len = 0  # pylint: disable=unused-variable
-        nonce_len = ca_key_len = ca_key_type_len = 0  # pylint: disable=unused-variable
-        ca_key_len = ca_key_type_len = ca_key_e_len = 0  # pylint: disable=unused-variable
-
-        key_id = principles = None  # pylint: disable=unused-variable
-        critical_options = extensions = None  # pylint: disable=unused-variable
-        nonce = ca_key = ca_key_type = None  # pylint: disable=unused-variable
-        ca_key_e = ca_key_n = None  # pylint: disable=unused-variable
-
         # Get the host key blob, F, and signature.
         ptr = 0
-        hostkey, hostkey_len, ptr = KexDH.__get_bytes(payload, ptr)
+        hostkey, _, ptr = KexDH.__get_bytes(payload, ptr)
 
         # If we are not supposed to parse the host key size (i.e.: it is a type that is of fixed size such as ed25519), then stop here.
         if not parse_host_key_size:
@@ -116,76 +116,106 @@ class KexDH:  # pragma: nocover
         # Now pick apart the host key blob.
         # Get the host key type (i.e.: 'ssh-rsa', 'ssh-ed25519', etc).
         ptr = 0
-        self.__hostkey_type, hostkey_type_len, ptr = KexDH.__get_bytes(hostkey, ptr)
+        hostkey_type, _, ptr = KexDH.__get_bytes(hostkey, ptr)
+        self.__hostkey_type = hostkey_type.decode('ascii')
+        self.out.d("Parsing host key type: %s" % self.__hostkey_type)
 
         # If this is an RSA certificate, skip over the nonce.
-        if self.__hostkey_type.startswith(b'ssh-rsa-cert-v0'):
-            nonce, nonce_len, ptr = KexDH.__get_bytes(hostkey, ptr)
+        if self.__hostkey_type.startswith('ssh-rsa-cert-v0'):
+            self.out.d("RSA certificate found, so skipping nonce.")
+            _, _, ptr = KexDH.__get_bytes(hostkey, ptr)  # Read & skip over the nonce.
 
         # The public key exponent.
-        hostkey_e, hostkey_e_len, ptr = KexDH.__get_bytes(hostkey, ptr)
+        hostkey_e, _, ptr = KexDH.__get_bytes(hostkey, ptr)
         self.__hostkey_e = int(binascii.hexlify(hostkey_e), 16)  # pylint: disable=unused-private-member
 
-        # Here is the modulus size & actual modulus of the host key public key.
-        hostkey_n, self.__hostkey_n_len, ptr = KexDH.__get_bytes(hostkey, ptr)
-        self.__hostkey_n = int(binascii.hexlify(hostkey_n), 16)  # pylint: disable=unused-private-member
+        # ED25519 moduli are fixed at 32 bytes.
+        if self.__hostkey_type == 'ssh-ed25519':
+            self.out.d("%s has a fixed host key modulus of 32." % self.__hostkey_type)
+            self.__hostkey_n_len = 32
+        else:
+            # Here is the modulus size & actual modulus of the host key public key.
+            hostkey_n, self.__hostkey_n_len, ptr = KexDH.__get_bytes(hostkey, ptr)
+            self.__hostkey_n = int(binascii.hexlify(hostkey_n), 16)  # pylint: disable=unused-private-member
 
-        # If this is an RSA certificate, continue parsing to extract the CA
-        # key.
-        if self.__hostkey_type.startswith(b'ssh-rsa-cert-v0'):
-            # Skip over the serial number.
-            ptr += 8
-
-            # Get the certificate type.
-            cert_type = int(binascii.hexlify(hostkey[ptr:ptr + 4]), 16)
-            ptr += 4
-
-            # Only SSH2_CERT_TYPE_HOST (2) makes sense in this context.
-            if cert_type == 2:
-
-                # Skip the key ID (this is the serial number of the
-                # certificate).
-                key_id, key_id_len, ptr = KexDH.__get_bytes(hostkey, ptr)
-
-                # The principles, which are... I don't know what.
-                principles, principles_len, ptr = KexDH.__get_bytes(hostkey, ptr)
-
-                # Skip over the timestamp that this certificate is valid after.
-                ptr += 8
-
-                # Skip over the timestamp that this certificate is valid before.
-                ptr += 8
-
-                # TODO: validate the principles, and time range.
-
-                # The critical options.
-                critical_options, critical_options_len, ptr = KexDH.__get_bytes(hostkey, ptr)
-
-                # Certificate extensions.
-                extensions, extensions_len, ptr = KexDH.__get_bytes(hostkey, ptr)
-
-                # Another nonce.
-                nonce, nonce_len, ptr = KexDH.__get_bytes(hostkey, ptr)
-
-                # Finally, we get to the CA key.
-                ca_key, ca_key_len, ptr = KexDH.__get_bytes(hostkey, ptr)
-
-                # Last in the host key blob is the CA signature.  It isn't
-                # interesting to us, so we won't bother parsing any further.
-                # The CA key has the modulus, however...
-                ptr = 0
-
-                # 'ssh-rsa', 'rsa-sha2-256', etc.
-                ca_key_type, ca_key_type_len, ptr = KexDH.__get_bytes(ca_key, ptr)
-
-                # CA's public key exponent.
-                ca_key_e, ca_key_e_len, ptr = KexDH.__get_bytes(ca_key, ptr)
-
-                # CA's modulus.  Bingo.
-                ca_key_n, self.__ca_n_len, ptr = KexDH.__get_bytes(ca_key, ptr)
+        # If this is a certificate, continue parsing to extract the CA type and key length.  Even though a hostkey type might be 'ssh-ed25519-cert-v01@openssh.com', its CA may still be RSA.
+        if self.__hostkey_type.startswith('ssh-rsa-cert-v0') or self.__hostkey_type.startswith('ssh-ed25519-cert-v0'):
+            # Get the CA key type and key length.
+            self.__ca_key_type, self.__ca_n_len = self.__parse_ca_key(hostkey, self.__hostkey_type, ptr)
+            self.out.d("KexDH.__parse_ca_key(): CA key type: [%s]; CA key length: %u" % (self.__ca_key_type, self.__ca_n_len))
 
         return hostkey
 
+    def __parse_ca_key(self, hostkey: bytes, hostkey_type: str, ptr: int) -> Tuple[str, int]:
+        ca_key_type = ''
+        ca_key_n_len = 0
+
+        # If this is a certificate, continue parsing to extract the CA type and key length.  Even though a hostkey type might be 'ssh-ed25519-cert-v01@openssh.com', its CA may still be RSA.
+        # if hostkey_type.startswith('ssh-rsa-cert-v0') or hostkey_type.startswith('ssh-ed25519-cert-v0'):
+        self.out.d("Parsing CA for hostkey type [%s]..." % hostkey_type)
+
+        # Skip over the serial number.
+        ptr += 8
+
+        # Get the certificate type.
+        cert_type = int(binascii.hexlify(hostkey[ptr:ptr + 4]), 16)
+        ptr += 4
+
+        # Only SSH2_CERT_TYPE_HOST (2) makes sense in this context.
+        if cert_type == 2:
+
+            # Skip the key ID (this is the serial number of the
+            # certificate).
+            key_id, key_id_len, ptr = KexDH.__get_bytes(hostkey, ptr)  # pylint: disable=unused-variable
+
+            # The principles, which are... I don't know what.
+            principles, principles_len, ptr = KexDH.__get_bytes(hostkey, ptr)  # pylint: disable=unused-variable
+
+            # Skip over the timestamp that this certificate is valid after.
+            ptr += 8
+
+            # Skip over the timestamp that this certificate is valid before.
+            ptr += 8
+
+            # TODO: validate the principles, and time range.
+
+            # The critical options.
+            critical_options, critical_options_len, ptr = KexDH.__get_bytes(hostkey, ptr)  # pylint: disable=unused-variable
+
+            # Certificate extensions.
+            extensions, extensions_len, ptr = KexDH.__get_bytes(hostkey, ptr)  # pylint: disable=unused-variable
+
+            # Another nonce.
+            nonce, nonce_len, ptr = KexDH.__get_bytes(hostkey, ptr)  # pylint: disable=unused-variable
+
+            # Finally, we get to the CA key.
+            ca_key, ca_key_len, ptr = KexDH.__get_bytes(hostkey, ptr)  # pylint: disable=unused-variable
+
+            # Last in the host key blob is the CA signature.  It isn't
+            # interesting to us, so we won't bother parsing any further.
+            # The CA key has the modulus, however...
+            ptr = 0
+
+            # 'ssh-rsa', 'rsa-sha2-256', etc.
+            ca_key_type_bytes, ca_key_type_len, ptr = KexDH.__get_bytes(ca_key, ptr)  # pylint: disable=unused-variable
+            ca_key_type = ca_key_type_bytes.decode('ascii')
+            self.out.d("Found CA type: [%s]" % ca_key_type)
+
+            # ED25519 CA's don't explicitly include the modulus size in the public key, since its fixed at 32 in all cases.
+            if ca_key_type == 'ssh-ed25519':
+                ca_key_n_len = 32
+            else:
+                # CA's public key exponent.
+                ca_key_e, ca_key_e_len, ptr = KexDH.__get_bytes(ca_key, ptr)  # pylint: disable=unused-variable
+
+                # CA's modulus.  Bingo.
+                ca_key_n, ca_key_n_len, ptr = KexDH.__get_bytes(ca_key, ptr)  # pylint: disable=unused-variable
+
+        else:
+            self.out.d("Certificate type %u found; this is not usually valid in the context of a host key!  Skipping it..." % cert_type)
+
+        return ca_key_type, ca_key_n_len
+
     @staticmethod
     def __get_bytes(buf: bytes, ptr: int) -> Tuple[bytes, int, int]:
         num_bytes = struct.unpack('>I', buf[ptr:ptr + 4])[0]
@@ -205,10 +235,18 @@ class KexDH:  # pragma: nocover
             size = size - 8
         return size
 
+    # Returns the hostkey type.
+    def get_hostkey_type(self) -> str:
+        return self.__hostkey_type
+
     # Returns the size of the hostkey, in bits.
     def get_hostkey_size(self) -> int:
         return KexDH.__adjust_key_size(self.__hostkey_n_len)
 
+    # Returns the CA type ('ssh-rsa', 'ssh-ed25519', etc).
+    def get_ca_type(self) -> str:
+        return self.__ca_key_type
+
     # Returns the size of the CA key, in bits.
     def get_ca_size(self) -> int:
         return KexDH.__adjust_key_size(self.__ca_n_len)
@@ -220,46 +258,46 @@ class KexDH:  # pragma: nocover
 
 
 class KexGroup1(KexDH):  # pragma: nocover
-    def __init__(self) -> None:
+    def __init__(self, out: 'OutputBuffer') -> None:
         # rfc2409: second oakley group
         p = int('ffffffffffffffffc90fdaa22168c234c4c6628b80dc1cd129024e088a67cc74020bbea63b139b22514a08798e3404ddef9519b3cd3a431b302b0a6df25f14374fe1356d6d51c245e485b576625e7ec6f44c42e9a637ed6b0bff5cb6f406b7edee386bfb5a899fa5ae9f24117c4b1fe649286651ece65381ffffffffffffffff', 16)
-        super(KexGroup1, self).__init__('KexGroup1', 'sha1', 2, p)
+        super(KexGroup1, self).__init__(out, 'KexGroup1', 'sha1', 2, p)
 
 
 class KexGroup14(KexDH):  # pragma: nocover
-    def __init__(self, hash_alg: str) -> None:
+    def __init__(self, out: 'OutputBuffer', hash_alg: str) -> None:
         # rfc3526: 2048-bit modp group
         p = int('ffffffffffffffffc90fdaa22168c234c4c6628b80dc1cd129024e088a67cc74020bbea63b139b22514a08798e3404ddef9519b3cd3a431b302b0a6df25f14374fe1356d6d51c245e485b576625e7ec6f44c42e9a637ed6b0bff5cb6f406b7edee386bfb5a899fa5ae9f24117c4b1fe649286651ece45b3dc2007cb8a163bf0598da48361c55d39a69163fa8fd24cf5f83655d23dca3ad961c62f356208552bb9ed529077096966d670c354e4abc9804f1746c08ca18217c32905e462e36ce3be39e772c180e86039b2783a2ec07a28fb5c55df06f4c52c9de2bcbf6955817183995497cea956ae515d2261898fa051015728e5a8aacaa68ffffffffffffffff', 16)
-        super(KexGroup14, self).__init__('KexGroup14', hash_alg, 2, p)
+        super(KexGroup14, self).__init__(out, 'KexGroup14', hash_alg, 2, p)
 
 
 class KexGroup14_SHA1(KexGroup14):
-    def __init__(self) -> None:
-        super(KexGroup14_SHA1, self).__init__('sha1')
+    def __init__(self, out: 'OutputBuffer') -> None:
+        super(KexGroup14_SHA1, self).__init__(out, 'sha1')
 
 
 class KexGroup14_SHA256(KexGroup14):
-    def __init__(self) -> None:
-        super(KexGroup14_SHA256, self).__init__('sha256')
+    def __init__(self, out: 'OutputBuffer') -> None:
+        super(KexGroup14_SHA256, self).__init__(out, 'sha256')
 
 
 class KexGroup16_SHA512(KexDH):
-    def __init__(self) -> None:
+    def __init__(self, out: 'OutputBuffer') -> None:
         # rfc3526: 4096-bit modp group
         p = int('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', 16)
-        super(KexGroup16_SHA512, self).__init__('KexGroup16_SHA512', 'sha512', 2, p)
+        super(KexGroup16_SHA512, self).__init__(out, 'KexGroup16_SHA512', 'sha512', 2, p)
 
 
 class KexGroup18_SHA512(KexDH):
-    def __init__(self) -> None:
+    def __init__(self, out: 'OutputBuffer') -> None:
         # rfc3526: 8192-bit modp group
         p = int('ffffffffffffffffc90fdaa22168c234c4c6628b80dc1cd129024e088a67cc74020bbea63b139b22514a08798e3404ddef9519b3cd3a431b302b0a6df25f14374fe1356d6d51c245e485b576625e7ec6f44c42e9a637ed6b0bff5cb6f406b7edee386bfb5a899fa5ae9f24117c4b1fe649286651ece45b3dc2007cb8a163bf0598da48361c55d39a69163fa8fd24cf5f83655d23dca3ad961c62f356208552bb9ed529077096966d670c354e4abc9804f1746c08ca18217c32905e462e36ce3be39e772c180e86039b2783a2ec07a28fb5c55df06f4c52c9de2bcbf6955817183995497cea956ae515d2261898fa051015728e5a8aaac42dad33170d04507a33a85521abdf1cba64ecfb850458dbef0a8aea71575d060c7db3970f85a6e1e4c7abf5ae8cdb0933d71e8c94e04a25619dcee3d2261ad2ee6bf12ffa06d98a0864d87602733ec86a64521f2b18177b200cbbe117577a615d6c770988c0bad946e208e24fa074e5ab3143db5bfce0fd108e4b82d120a92108011a723c12a787e6d788719a10bdba5b2699c327186af4e23c1a946834b6150bda2583e9ca2ad44ce8dbbbc2db04de8ef92e8efc141fbecaa6287c59474e6bc05d99b2964fa090c3a2233ba186515be7ed1f612970cee2d7afb81bdd762170481cd0069127d5b05aa993b4ea988d8fddc186ffb7dc90a6c08f4df435c93402849236c3fab4d27c7026c1d4dcb2602646dec9751e763dba37bdf8ff9406ad9e530ee5db382f413001aeb06a53ed9027d831179727b0865a8918da3edbebcf9b14ed44ce6cbaced4bb1bdb7f1447e6cc254b332051512bd7af426fb8f401378cd2bf5983ca01c64b92ecf032ea15d1721d03f482d7ce6e74fef6d55e702f46980c82b5a84031900b1c9e59e7c97fbec7e8f323a97a7e36cc88be0f1d45b7ff585ac54bd407b22b4154aacc8f6d7ebf48e1d814cc5ed20f8037e0a79715eef29be32806a1d58bb7c5da76f550aa3d8a1fbff0eb19ccb1a313d55cda56c9ec2ef29632387fe8d76e3c0468043e8f663f4860ee12bf2d5b0b7474d6e694f91e6dbe115974a3926f12fee5e438777cb6a932df8cd8bec4d073b931ba3bc832b68d9dd300741fa7bf8afc47ed2576f6936ba424663aab639c5ae4f5683423b4742bf1c978238f16cbe39d652de3fdb8befc848ad922222e04a4037c0713eb57a81a23f0c73473fc646cea306b4bcbc8862f8385ddfa9d4b7fa2c087e879683303ed5bdd3a062b3cf5b3a278a66d2a13f83f44f82ddf310ee074ab6a364597e899a0255dc164f31cc50846851df9ab48195ded7ea1b1d510bd7ee74d73faf36bc31ecfa268359046f4eb879f924009438b481c6cd7889a002ed5ee382bc9190da6fc026e479558e4475677e9aa9e3050e2765694dfc81f56e880b96e7160c980dd98edd3dfffffffffffffffff', 16)
-        super(KexGroup18_SHA512, self).__init__('KexGroup18_SHA512', 'sha512', 2, p)
+        super(KexGroup18_SHA512, self).__init__(out, 'KexGroup18_SHA512', 'sha512', 2, p)
 
 
 class KexCurve25519_SHA256(KexDH):
-    def __init__(self) -> None:
-        super(KexCurve25519_SHA256, self).__init__('KexCurve25519_SHA256', 'sha256', 0, 0)
+    def __init__(self, out: 'OutputBuffer') -> None:
+        super(KexCurve25519_SHA256, self).__init__(out, 'KexCurve25519_SHA256', 'sha256', 0, 0)
 
     # To start an ED25519 kex, we simply send a random 256-bit number as the
     # public key.
@@ -271,8 +309,8 @@ class KexCurve25519_SHA256(KexDH):
 
 
 class KexNISTP256(KexDH):
-    def __init__(self) -> None:
-        super(KexNISTP256, self).__init__('KexNISTP256', 'sha256', 0, 0)
+    def __init__(self, out: 'OutputBuffer') -> None:
+        super(KexNISTP256, self).__init__(out, 'KexNISTP256', 'sha256', 0, 0)
 
     # Because the server checks that the value sent here is valid (i.e.: it lies
     # on the curve, among other things), we would have to write a lot of code
@@ -286,8 +324,8 @@ class KexNISTP256(KexDH):
 
 
 class KexNISTP384(KexDH):
-    def __init__(self) -> None:
-        super(KexNISTP384, self).__init__('KexNISTP384', 'sha256', 0, 0)
+    def __init__(self, out: 'OutputBuffer') -> None:
+        super(KexNISTP384, self).__init__(out, 'KexNISTP384', 'sha256', 0, 0)
 
     # See comment for KexNISTP256.send_init().
     def send_init(self, s: 'SSH_Socket', init_msg: int = Protocol.MSG_KEXDH_INIT) -> None:
@@ -297,8 +335,8 @@ class KexNISTP384(KexDH):
 
 
 class KexNISTP521(KexDH):
-    def __init__(self) -> None:
-        super(KexNISTP521, self).__init__('KexNISTP521', 'sha256', 0, 0)
+    def __init__(self, out: 'OutputBuffer') -> None:
+        super(KexNISTP521, self).__init__(out, 'KexNISTP521', 'sha256', 0, 0)
 
     # See comment for KexNISTP256.send_init().
     def send_init(self, s: 'SSH_Socket', init_msg: int = Protocol.MSG_KEXDH_INIT) -> None:
@@ -308,8 +346,8 @@ class KexNISTP521(KexDH):
 
 
 class KexGroupExchange(KexDH):
-    def __init__(self, classname: str, hash_alg: str) -> None:
-        super(KexGroupExchange, self).__init__(classname, hash_alg, 0, 0)
+    def __init__(self, out: 'OutputBuffer', classname: str, hash_alg: str) -> None:
+        super(KexGroupExchange, self).__init__(out, classname, hash_alg, 0, 0)
 
     def send_init(self, s: 'SSH_Socket', init_msg: int = Protocol.MSG_KEXDH_GEX_REQUEST) -> None:
         self.send_init_gex(s)
@@ -358,10 +396,10 @@ class KexGroupExchange(KexDH):
 
 
 class KexGroupExchange_SHA1(KexGroupExchange):
-    def __init__(self) -> None:
-        super(KexGroupExchange_SHA1, self).__init__('KexGroupExchange_SHA1', 'sha1')
+    def __init__(self, out: 'OutputBuffer') -> None:
+        super(KexGroupExchange_SHA1, self).__init__(out, 'KexGroupExchange_SHA1', 'sha1')
 
 
 class KexGroupExchange_SHA256(KexGroupExchange):
-    def __init__(self) -> None:
-        super(KexGroupExchange_SHA256, self).__init__('KexGroupExchange_SHA256', 'sha256')
+    def __init__(self, out: 'OutputBuffer') -> None:
+        super(KexGroupExchange_SHA256, self).__init__(out, 'KexGroupExchange_SHA256', 'sha256')
diff --git a/src/ssh_audit/policy.py b/src/ssh_audit/policy.py
index 2e28699..7fb3fb7 100644
--- a/src/ssh_audit/policy.py
+++ b/src/ssh_audit/policy.py
@@ -21,6 +21,8 @@
    OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
    THE SOFTWARE.
 """
+import copy
+import json
 import sys
 
 from typing import Dict, List, Tuple
@@ -28,9 +30,9 @@ from typing import Optional, Any, Union, cast
 from datetime import date
 
 from ssh_audit import exitcodes
-from ssh_audit.ssh2_kex import SSH2_Kex  # pylint: disable=unused-import
-from ssh_audit.banner import Banner  # pylint: disable=unused-import
+from ssh_audit.banner import Banner
 from ssh_audit.globals import SNAP_PACKAGE, SNAP_PERMISSIONS_ERROR
+from ssh_audit.ssh2_kex import SSH2_Kex
 
 
 # Validates policy files and performs policy testing
@@ -87,8 +89,9 @@ class Policy:
 
     }
 
+    WARNING_DEPRECATED_DIRECTIVES = "\nWARNING: this policy is using deprecated features.  Future versions of ssh-audit may remove support for them.  Re-generating the policy file is perhaps the most straight-forward way of resolving this issue.  Manually converting the 'hostkey_size_*', 'cakey_size_*', and 'dh_modulus_size_*' directives into the new format is another option.\n"
 
-    def __init__(self, policy_file: Optional[str] = None, policy_data: Optional[str] = None, manual_load: bool = False) -> None:
+    def __init__(self, policy_file: Optional[str] = None, policy_data: Optional[str] = None, manual_load: bool = False, json_output: bool = False) -> None:
         self._name: Optional[str] = None
         self._version: Optional[str] = None
         self._banner: Optional[str] = None
@@ -98,13 +101,19 @@ class Policy:
         self._kex: Optional[List[str]] = None
         self._ciphers: Optional[List[str]] = None
         self._macs: Optional[List[str]] = None
-        self._hostkey_sizes: Optional[Dict[str, int]] = None
+        self._hostkey_sizes: Optional[Dict[str, Dict[str, Union[int, str, bytes]]]] = None
         self._cakey_sizes: Optional[Dict[str, int]] = None
         self._dh_modulus_sizes: Optional[Dict[str, int]] = None
         self._server_policy = True
 
         self._name_and_version: str = ''
 
+        # If invoked while JSON output is expected, send warnings to stderr instead of stdout (which would corrupt the JSON output).
+        if json_output:
+            self._warning_target = sys.stderr
+        else:
+            self._warning_target = sys.stdout
+
         # Ensure that only one mode was specified.
         num_modes = 0
         if policy_file is not None:
@@ -154,7 +163,7 @@ class Policy:
             key = key.strip()
             val = val.strip()
 
-            if key not in ['name', 'version', 'banner', 'compressions', 'host keys', 'optional host keys', 'key exchanges', 'ciphers', 'macs', 'client policy'] and not key.startswith('hostkey_size_') and not key.startswith('cakey_size_') and not key.startswith('dh_modulus_size_'):
+            if key not in ['name', 'version', 'banner', 'compressions', 'host keys', 'optional host keys', 'key exchanges', 'ciphers', 'macs', 'client policy', 'host_key_sizes', 'dh_modulus_sizes'] and not key.startswith('hostkey_size_') and not key.startswith('cakey_size_') and not key.startswith('dh_modulus_size_'):
                 raise ValueError("invalid field found in policy: %s" % line)
 
             if key in ['name', 'banner']:
@@ -173,8 +182,10 @@ class Policy:
                     self._name = val
                 elif key == 'banner':
                     self._banner = val
+
             elif key == 'version':
                 self._version = val
+
             elif key in ['compressions', 'host keys', 'optional host keys', 'key exchanges', 'ciphers', 'macs']:
                 try:
                     algs = val.split(',')
@@ -197,21 +208,59 @@ class Policy:
                     self._ciphers = algs
                 elif key == 'macs':
                     self._macs = algs
-            elif key.startswith('hostkey_size_'):
+
+            elif key.startswith('hostkey_size_'):  # Old host key size format.
+                print(Policy.WARNING_DEPRECATED_DIRECTIVES, file=self._warning_target)  # Warn the user that the policy file is using deprecated directives.
+
                 hostkey_type = key[13:]
+                hostkey_size = int(val)
+
                 if self._hostkey_sizes is None:
                     self._hostkey_sizes = {}
-                self._hostkey_sizes[hostkey_type] = int(val)
-            elif key.startswith('cakey_size_'):
-                cakey_type = key[11:]
-                if self._cakey_sizes is None:
-                    self._cakey_sizes = {}
-                self._cakey_sizes[cakey_type] = int(val)
-            elif key.startswith('dh_modulus_size_'):
-                dh_modulus_type = key[16:]
+
+                self._hostkey_sizes[hostkey_type] = {'hostkey_size': hostkey_size, 'ca_key_type': '', 'ca_key_size': 0}
+
+            elif key.startswith('cakey_size_'):  # Old host key size format.
+                print(Policy.WARNING_DEPRECATED_DIRECTIVES, file=self._warning_target)  # Warn the user that the policy file is using deprecated directives.
+
+                hostkey_type = key[11:]
+                ca_key_size = int(val)
+
+                ca_key_type = 'ssh-ed25519'
+                if hostkey_type in ['ssh-rsa-cert-v01@openssh.com', 'rsa-sha2-256-cert-v01@openssh.com', 'rsa-sha2-512-cert-v01@openssh.com']:
+                    ca_key_type = 'ssh-rsa'
+
+                if self._hostkey_sizes is None:
+                    self._hostkey_sizes = {}
+                self._hostkey_sizes[hostkey_type] = {'hostkey_size': hostkey_size, 'ca_key_type': ca_key_type, 'ca_key_size': ca_key_size}
+
+            elif key == 'host_key_sizes':  # New host key size format.
+                self._hostkey_sizes = json.loads(val)
+
+                # Fill in the trimmed fields that were omitted from the policy.
+                if self._hostkey_sizes is not None:
+                    for host_key_type in self._hostkey_sizes:
+                        if 'ca_key_type' not in self._hostkey_sizes[host_key_type]:
+                            self._hostkey_sizes[host_key_type]['ca_key_type'] = ''
+                        if 'ca_key_size' not in self._hostkey_sizes[host_key_type]:
+                            self._hostkey_sizes[host_key_type]['ca_key_size'] = 0
+                        if 'raw_hostkey_bytes' not in self._hostkey_sizes[host_key_type]:
+                            self._hostkey_sizes[host_key_type]['raw_hostkey_bytes'] = b''
+
+            elif key.startswith('dh_modulus_size_'):  # Old DH modulus format.
+                print(Policy.WARNING_DEPRECATED_DIRECTIVES, file=self._warning_target)  # Warn the user that the policy file is using deprecated directives.
+
+                dh_type = key[16:]
+                dh_size = int(val)
+
                 if self._dh_modulus_sizes is None:
                     self._dh_modulus_sizes = {}
-                self._dh_modulus_sizes[dh_modulus_type] = int(val)
+
+                self._dh_modulus_sizes[dh_type] = dh_size
+
+            elif key == 'dh_modulus_sizes':  # New DH modulus format.
+                self._dh_modulus_sizes = json.loads(val)
+
             elif key.startswith('client policy') and val.lower() == 'true':
                 self._server_policy = False
 
@@ -243,10 +292,9 @@ class Policy:
         kex_algs = None
         ciphers = None
         macs = None
-        rsa_hostkey_sizes_str = ''
-        rsa_cakey_sizes_str = ''
         dh_modulus_sizes_str = ''
         client_policy_str = ''
+        host_keys_json = ''
 
         if client_audit:
             client_policy_str = "\n# Set to true to signify this is a policy for clients, not servers.\nclient policy = true\n"
@@ -262,26 +310,23 @@ class Policy:
                 ciphers = ', '.join(kex.server.encryption)
             if kex.server.mac is not None:
                 macs = ', '.join(kex.server.mac)
-            if kex.rsa_key_sizes():
-                rsa_key_sizes_dict = kex.rsa_key_sizes()
-                for host_key_type in sorted(rsa_key_sizes_dict):
-                    hostkey_size, cakey_size = rsa_key_sizes_dict[host_key_type]
 
-                    rsa_hostkey_sizes_str = "%shostkey_size_%s = %d\n" % (rsa_hostkey_sizes_str, host_key_type, hostkey_size)
-                    if cakey_size != -1:
-                        rsa_cakey_sizes_str = "%scakey_size_%s = %d\n" % (rsa_cakey_sizes_str, host_key_type, cakey_size)
+            if kex.host_keys():
+
+                # Make a deep copy of the host keys dict, then delete all the raw hostkey bytes from the copy.
+                host_keys_trimmed = copy.deepcopy(kex.host_keys())
+                for hostkey_alg in host_keys_trimmed:
+                    del host_keys_trimmed[hostkey_alg]['raw_hostkey_bytes']
+
+                    # Delete the CA signature if any of its fields are empty.
+                    if host_keys_trimmed[hostkey_alg]['ca_key_type'] == '' or host_keys_trimmed[hostkey_alg]['ca_key_size'] == 0:
+                        del host_keys_trimmed[hostkey_alg]['ca_key_type']
+                        del host_keys_trimmed[hostkey_alg]['ca_key_size']
+
+                host_keys_json = "\n# Dictionary containing all host key and size information.  Optionally contains the certificate authority's signature algorithm ('ca_key_type') and signature length ('ca_key_size'), if any.\nhost_key_sizes = %s\n" % json.dumps(host_keys_trimmed)
 
-                if len(rsa_hostkey_sizes_str) > 0:
-                    rsa_hostkey_sizes_str = "\n# RSA host key sizes.\n%s" % rsa_hostkey_sizes_str
-                if len(rsa_cakey_sizes_str) > 0:
-                    rsa_cakey_sizes_str = "\n# RSA CA key sizes.\n%s" % rsa_cakey_sizes_str
             if kex.dh_modulus_sizes():
-                dh_modulus_sizes_dict = kex.dh_modulus_sizes()
-                for gex_type in sorted(dh_modulus_sizes_dict):
-                    modulus_size, _ = dh_modulus_sizes_dict[gex_type]
-                    dh_modulus_sizes_str = "%sdh_modulus_size_%s = %d\n" % (dh_modulus_sizes_str, gex_type, modulus_size)
-                if len(dh_modulus_sizes_str) > 0:
-                    dh_modulus_sizes_str = "\n# Group exchange DH modulus sizes.\n%s" % dh_modulus_sizes_str
+                dh_modulus_sizes_str = "\n# Group exchange DH modulus sizes.\ndh_modulus_sizes = %s\n" % json.dumps(kex.dh_modulus_sizes())
 
 
         policy_data = '''#
@@ -299,7 +344,7 @@ version = 1
 
 # The compression options that must match exactly (order matters).  Commented out to ignore by default.
 # compressions = %s
-%s%s%s
+%s%s
 # The host key types that must match exactly (order matters).
 host keys = %s
 
@@ -314,7 +359,7 @@ ciphers = %s
 
 # The MACs that must match exactly (order matters).
 macs = %s
-''' % (source, today, client_policy_str, source, today, banner, compressions, rsa_hostkey_sizes_str, rsa_cakey_sizes_str, dh_modulus_sizes_str, host_keys, kex_algs, ciphers, macs)
+''' % (source, today, client_policy_str, source, today, banner, compressions, host_keys_json, dh_modulus_sizes_str, host_keys, kex_algs, ciphers, macs)
 
         return policy_data
 
@@ -351,23 +396,29 @@ macs = %s
             hostkey_types = list(self._hostkey_sizes.keys())
             hostkey_types.sort()  # Sorted to make testing output repeatable.
             for hostkey_type in hostkey_types:
-                expected_hostkey_size = self._hostkey_sizes[hostkey_type]
-                if hostkey_type in kex.rsa_key_sizes():
-                    actual_hostkey_size, actual_cakey_size = kex.rsa_key_sizes()[hostkey_type]
+                expected_hostkey_size = self._hostkey_sizes[hostkey_type]['hostkey_size']
+                server_host_keys = kex.host_keys()
+                if hostkey_type in server_host_keys:
+                    actual_hostkey_size = server_host_keys[hostkey_type]['hostkey_size']
                     if actual_hostkey_size != expected_hostkey_size:
                         ret = False
-                        self._append_error(errors, 'RSA host key (%s) sizes' % hostkey_type, [str(expected_hostkey_size)], None, [str(actual_hostkey_size)])
+                        self._append_error(errors, 'Host key (%s) sizes' % hostkey_type, [str(expected_hostkey_size)], None, [str(actual_hostkey_size)])
 
-        if self._cakey_sizes is not None:
-            hostkey_types = list(self._cakey_sizes.keys())
-            hostkey_types.sort()  # Sorted to make testing output repeatable.
-            for hostkey_type in hostkey_types:
-                expected_cakey_size = self._cakey_sizes[hostkey_type]
-                if hostkey_type in kex.rsa_key_sizes():
-                    actual_hostkey_size, actual_cakey_size = kex.rsa_key_sizes()[hostkey_type]
-                    if actual_cakey_size != expected_cakey_size:
-                        ret = False
-                        self._append_error(errors, 'RSA CA key (%s) sizes' % hostkey_type, [str(expected_cakey_size)], None, [str(actual_cakey_size)])
+                    # If we have expected CA signatures set, check them against what the server returned.
+                    if self._hostkey_sizes is not None and len(cast(str, self._hostkey_sizes[hostkey_type]['ca_key_type'])) > 0 and cast(int, self._hostkey_sizes[hostkey_type]['ca_key_size']) > 0:
+                        expected_ca_key_type = cast(str, self._hostkey_sizes[hostkey_type]['ca_key_type'])
+                        expected_ca_key_size = cast(int, self._hostkey_sizes[hostkey_type]['ca_key_size'])
+                        actual_ca_key_type = cast(str, server_host_keys[hostkey_type]['ca_key_type'])
+                        actual_ca_key_size = cast(int, server_host_keys[hostkey_type]['ca_key_size'])
+
+                        # Ensure that the CA signature type is what's expected (i.e.: the server doesn't have an RSA sig when we're expecting an ED25519 sig).
+                        if actual_ca_key_type != expected_ca_key_type:
+                            ret = False
+                            self._append_error(errors, 'CA signature type', [expected_ca_key_type], None, [actual_ca_key_type])
+                        # Ensure that the actual and expected signature sizes match.
+                        elif actual_ca_key_size != expected_ca_key_size:
+                            ret = False
+                            self._append_error(errors, 'CA signature size (%s)' % actual_ca_key_type, [str(expected_ca_key_size)], None, [str(actual_ca_key_size)])
 
         if kex.kex_algorithms != self._kex:
             ret = False
@@ -387,7 +438,7 @@ macs = %s
             for dh_modulus_type in dh_modulus_types:
                 expected_dh_modulus_size = self._dh_modulus_sizes[dh_modulus_type]
                 if dh_modulus_type in kex.dh_modulus_sizes():
-                    actual_dh_modulus_size, _ = kex.dh_modulus_sizes()[dh_modulus_type]
+                    actual_dh_modulus_size = kex.dh_modulus_sizes()[dh_modulus_type]
                     if expected_dh_modulus_size != actual_dh_modulus_size:
                         ret = False
                         self._append_error(errors, 'Group exchange (%s) modulus sizes' % dh_modulus_type, [str(expected_dh_modulus_size)], None, [str(actual_dh_modulus_size)])
@@ -449,12 +500,12 @@ macs = %s
 
 
     @staticmethod
-    def load_builtin_policy(policy_name: str) -> Optional['Policy']:
+    def load_builtin_policy(policy_name: str, json_output: bool = False) -> Optional['Policy']:
         '''Returns a Policy with the specified built-in policy name loaded, or None if no policy of that name exists.'''
         p = None
         if policy_name in Policy.BUILTIN_POLICIES:
             policy_struct = Policy.BUILTIN_POLICIES[policy_name]
-            p = Policy(manual_load=True)
+            p = Policy(manual_load=True, json_output=json_output)
             policy_name_without_version = policy_name[0:policy_name.rfind(' (')]
             p._name = policy_name_without_version  # pylint: disable=protected-access
             p._version = cast(str, policy_struct['version'])  # pylint: disable=protected-access
@@ -465,7 +516,7 @@ macs = %s
             p._kex = cast(Optional[List[str]], policy_struct['kex'])  # pylint: disable=protected-access
             p._ciphers = cast(Optional[List[str]], policy_struct['ciphers'])  # pylint: disable=protected-access
             p._macs = cast(Optional[List[str]], policy_struct['macs'])  # pylint: disable=protected-access
-            p._hostkey_sizes = cast(Optional[Dict[str, int]], policy_struct['hostkey_sizes'])  # pylint: disable=protected-access
+            p._hostkey_sizes = cast(Optional[Dict[str, Dict[str, Union[int, str, bytes]]]], policy_struct['hostkey_sizes'])  # pylint: disable=protected-access
             p._cakey_sizes = cast(Optional[Dict[str, int]], policy_struct['cakey_sizes'])  # pylint: disable=protected-access
             p._dh_modulus_sizes = cast(Optional[Dict[str, int]], policy_struct['dh_modulus_sizes'])  # pylint: disable=protected-access
             p._server_policy = cast(bool, policy_struct['server_policy'])  # pylint: disable=protected-access
diff --git a/src/ssh_audit/ssh2_kex.py b/src/ssh_audit/ssh2_kex.py
index 0c31f3d..d71724f 100644
--- a/src/ssh_audit/ssh2_kex.py
+++ b/src/ssh_audit/ssh2_kex.py
@@ -22,17 +22,18 @@
    OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
    THE SOFTWARE.
 """
-# pylint: disable=unused-import
-from typing import Dict, List, Set, Sequence, Tuple, Iterable  # noqa: F401
-from typing import Callable, Optional, Union, Any  # noqa: F401
+from typing import Dict, List
+from typing import Union
 
-from ssh_audit.ssh2_kexparty import SSH2_KexParty
+from ssh_audit.outputbuffer import OutputBuffer
 from ssh_audit.readbuf import ReadBuf
+from ssh_audit.ssh2_kexparty import SSH2_KexParty
 from ssh_audit.writebuf import WriteBuf
 
 
 class SSH2_Kex:
-    def __init__(self, cookie: bytes, kex_algs: List[str], key_algs: List[str], cli: 'SSH2_KexParty', srv: 'SSH2_KexParty', follows: bool, unused: int = 0) -> None:
+    def __init__(self, outputbuffer: 'OutputBuffer', cookie: bytes, kex_algs: List[str], key_algs: List[str], cli: 'SSH2_KexParty', srv: 'SSH2_KexParty', follows: bool, unused: int = 0) -> None:  # pylint: disable=too-many-arguments
+        self.__outputbuffer = outputbuffer
         self.__cookie = cookie
         self.__kex_algs = kex_algs
         self.__key_algs = key_algs
@@ -41,9 +42,8 @@ class SSH2_Kex:
         self.__follows = follows
         self.__unused = unused
 
-        self.__rsa_key_sizes: Dict[str, Tuple[int, int]] = {}
-        self.__dh_modulus_sizes: Dict[str, Tuple[int, int]] = {}
-        self.__host_keys: Dict[str, bytes] = {}
+        self.__dh_modulus_sizes: Dict[str, int] = {}
+        self.__host_keys: Dict[str, Dict[str, Union[bytes, str, int]]] = {}
 
     @property
     def cookie(self) -> bytes:
@@ -75,22 +75,20 @@ class SSH2_Kex:
     def unused(self) -> int:
         return self.__unused
 
-    def set_rsa_key_size(self, rsa_type: str, hostkey_size: int, ca_size: int = -1) -> None:
-        self.__rsa_key_sizes[rsa_type] = (hostkey_size, ca_size)
-
-    def rsa_key_sizes(self) -> Dict[str, Tuple[int, int]]:
-        return self.__rsa_key_sizes
-
     def set_dh_modulus_size(self, gex_alg: str, modulus_size: int) -> None:
-        self.__dh_modulus_sizes[gex_alg] = (modulus_size, -1)
+        self.__dh_modulus_sizes[gex_alg] = modulus_size
 
-    def dh_modulus_sizes(self) -> Dict[str, Tuple[int, int]]:
+    def dh_modulus_sizes(self) -> Dict[str, int]:
         return self.__dh_modulus_sizes
 
-    def set_host_key(self, key_type: str, hostkey: bytes) -> None:
-        self.__host_keys[key_type] = hostkey
+    def set_host_key(self, key_type: str, raw_hostkey_bytes: bytes, hostkey_size: int, ca_key_type: str, ca_key_size: int) -> None:
 
-    def host_keys(self) -> Dict[str, bytes]:
+        if key_type not in self.__host_keys:
+            self.__host_keys[key_type] = {'raw_hostkey_bytes': raw_hostkey_bytes, 'hostkey_size': hostkey_size, 'ca_key_type': ca_key_type, 'ca_key_size': ca_key_size}
+        else:  # A host key may only have one CA signature...
+            self.__outputbuffer.d("WARNING: called SSH2_Kex.set_host_key() multiple times with the same host key type (%s)!  Existing info: %r, %r, %r; Duplicate (ignored) info: %r, %r, %r" % (key_type, self.__host_keys[key_type]['hostkey_size'], self.__host_keys[key_type]['ca_key_type'], self.__host_keys[key_type]['ca_key_size'], hostkey_size, ca_key_type, ca_key_size))
+
+    def host_keys(self) -> Dict[str, Dict[str, Union[bytes, str, int]]]:
         return self.__host_keys
 
     def write(self, wbuf: 'WriteBuf') -> None:
@@ -115,7 +113,7 @@ class SSH2_Kex:
         return wbuf.write_flush()
 
     @classmethod
-    def parse(cls, payload: bytes) -> 'SSH2_Kex':
+    def parse(cls, outputbuffer: 'OutputBuffer', payload: bytes) -> 'SSH2_Kex':
         buf = ReadBuf(payload)
         cookie = buf.read(16)
         kex_algs = buf.read_list()
@@ -132,5 +130,5 @@ class SSH2_Kex:
         unused = buf.read_int()
         cli = SSH2_KexParty(cli_enc, cli_mac, cli_compression, cli_languages)
         srv = SSH2_KexParty(srv_enc, srv_mac, srv_compression, srv_languages)
-        kex = cls(cookie, kex_algs, key_algs, cli, srv, follows, unused)
+        kex = cls(outputbuffer, cookie, kex_algs, key_algs, cli, srv, follows, unused)
         return kex
diff --git a/src/ssh_audit/ssh_audit.py b/src/ssh_audit/ssh_audit.py
index 2ebbc37..bc86153 100755
--- a/src/ssh_audit/ssh_audit.py
+++ b/src/ssh_audit/ssh_audit.py
@@ -34,7 +34,7 @@ import traceback
 
 # pylint: disable=unused-import
 from typing import Dict, List, Set, Sequence, Tuple, Iterable  # noqa: F401
-from typing import Callable, Optional, Union, Any  # noqa: F401
+from typing import cast, Callable, Optional, Union, Any  # noqa: F401
 
 from ssh_audit.globals import SNAP_PACKAGE
 from ssh_audit.globals import SNAP_PERMISSIONS_ERROR
@@ -107,10 +107,10 @@ def usage(uout: OutputBuffer, err: Optional[str] = None) -> None:
     sys.exit(retval)
 
 
-def output_algorithms(out: OutputBuffer, title: str, alg_db: Dict[str, Dict[str, List[List[Optional[str]]]]], alg_type: str, algorithms: List[str], unknown_algs: List[str], is_json_output: bool, program_retval: int, maxlen: int = 0, alg_sizes: Optional[Dict[str, Tuple[int, int]]] = None) -> int:  # pylint: disable=too-many-arguments
+def output_algorithms(out: OutputBuffer, title: str, alg_db: Dict[str, Dict[str, List[List[Optional[str]]]]], alg_type: str, algorithms: List[str], unknown_algs: List[str], is_json_output: bool, program_retval: int, maxlen: int = 0, host_keys: Optional[Dict[str, Dict[str, Union[bytes, str, int]]]] = None, dh_modulus_sizes: Optional[Dict[str, int]] = None) -> int:  # pylint: disable=too-many-arguments
     with out:
         for algorithm in algorithms:
-            program_retval = output_algorithm(out, alg_db, alg_type, algorithm, unknown_algs, program_retval, maxlen, alg_sizes)
+            program_retval = output_algorithm(out, alg_db, alg_type, algorithm, unknown_algs, program_retval, maxlen, host_keys=host_keys, dh_modulus_sizes=dh_modulus_sizes)
     if not out.is_section_empty() and not is_json_output:
         out.head('# ' + title)
         out.flush_section()
@@ -119,7 +119,7 @@ def output_algorithms(out: OutputBuffer, title: str, alg_db: Dict[str, Dict[str,
     return program_retval
 
 
-def output_algorithm(out: OutputBuffer, alg_db: Dict[str, Dict[str, List[List[Optional[str]]]]], alg_type: str, alg_name: str, unknown_algs: List[str], program_retval: int, alg_max_len: int = 0, alg_sizes: Optional[Dict[str, Tuple[int, int]]] = None) -> int:
+def output_algorithm(out: OutputBuffer, alg_db: Dict[str, Dict[str, List[List[Optional[str]]]]], alg_type: str, alg_name: str, unknown_algs: List[str], program_retval: int, alg_max_len: int = 0, host_keys: Optional[Dict[str, Dict[str, Union[bytes, str, int]]]] = None, dh_modulus_sizes: Optional[Dict[str, int]] = None) -> int:  # pylint: disable=too-many-arguments
     prefix = '(' + alg_type + ') '
     if alg_max_len == 0:
         alg_max_len = len(alg_name)
@@ -128,13 +128,23 @@ def output_algorithm(out: OutputBuffer, alg_db: Dict[str, Dict[str, List[List[Op
     # If this is an RSA host key or DH GEX, append the size to its name and fix
     # the padding.
     alg_name_with_size = None
-    if (alg_sizes is not None) and (alg_name in alg_sizes):
-        hostkey_size, ca_size = alg_sizes[alg_name]
-        if ca_size > 0:
-            alg_name_with_size = '%s (%d-bit cert/%d-bit CA)' % (alg_name, hostkey_size, ca_size)
+    if (dh_modulus_sizes is not None) and (alg_name in dh_modulus_sizes):
+        alg_name_with_size = '%s (%u-bit)' % (alg_name, dh_modulus_sizes[alg_name])
+        padding = padding[0:-11]
+    elif (host_keys is not None) and (alg_name in host_keys):
+        hostkey_size = cast(int, host_keys[alg_name]['hostkey_size'])
+        ca_key_type = cast(str, host_keys[alg_name]['ca_key_type'])
+        ca_key_size = cast(int, host_keys[alg_name]['ca_key_size'])
+
+        # If this is an RSA variant, just print "RSA".
+        if ca_key_type in HostKeyTest.RSA_FAMILY:
+            ca_key_type = "RSA"
+
+        if len(ca_key_type) > 0 and ca_key_size > 0:
+            alg_name_with_size = '%s (%u-bit cert/%u-bit %s CA)' % (alg_name, hostkey_size, ca_key_size, ca_key_type)
             padding = padding[0:-15]
-        else:
-            alg_name_with_size = '%s (%d-bit)' % (alg_name, hostkey_size)
+        elif alg_name in HostKeyTest.RSA_FAMILY:
+            alg_name_with_size = '%s (%u-bit)' % (alg_name, hostkey_size)
             padding = padding[0:-11]
 
     # If this is a kex algorithm and starts with 'gss-', then normalize its name (i.e.: 'gss-gex-sha1-vz8J1E9PzLr8b1K+0remTg==' => 'gss-gex-sha1-*').  The base64 field can vary, so we'll convert it to the wildcard that our database uses and we'll just resume doing a straight match like all other algorithm names.
@@ -289,36 +299,36 @@ def output_security(out: OutputBuffer, banner: Optional[Banner], client_audit: b
 
 def output_fingerprints(out: OutputBuffer, algs: Algorithms, is_json_output: bool) -> None:
     with out:
-        fps = []
+        fps = {}
         if algs.ssh1kex is not None:
             name = 'ssh-rsa1'
             fp = Fingerprint(algs.ssh1kex.host_key_fingerprint_data)
             # bits = algs.ssh1kex.host_key_bits
-            fps.append((name, fp))
+            fps[name] = fp
         if algs.ssh2kex is not None:
             host_keys = algs.ssh2kex.host_keys()
             for host_key_type in algs.ssh2kex.host_keys():
                 if host_keys[host_key_type] is None:
                     continue
 
-                fp = Fingerprint(host_keys[host_key_type])
+                fp = Fingerprint(cast(bytes, host_keys[host_key_type]['raw_hostkey_bytes']))
 
                 # Workaround for Python's order-indifference in dicts.  We might get a random RSA type (ssh-rsa, rsa-sha2-256, or rsa-sha2-512), so running the tool against the same server three times may give three different host key types here.  So if we have any RSA type, we will simply hard-code it to 'ssh-rsa'.
                 if host_key_type in HostKeyTest.RSA_FAMILY:
                     host_key_type = 'ssh-rsa'
 
-                # Skip over certificate host types (or we would return invalid fingerprints).
+                # Skip over certificate host types (or we would return invalid fingerprints), and only add one fingerprint in the RSA family.
                 if '-cert-' not in host_key_type:
-                    fps.append((host_key_type, fp))
+                    fps[host_key_type] = fp
         # Similarly, the host keys can be processed in random order due to Python's order-indifference in dicts.  So we sort this list before printing; this makes automated testing possible.
-        fps = sorted(fps)
-        for fpp in fps:
-            name, fp = fpp
-            out.good('(fin) {}: {}'.format(name, fp.sha256))
+        fp_types = sorted(fps.keys())
+        for fp_type in fp_types:
+            fp = fps[fp_type]
+            out.good('(fin) {}: {}'.format(fp_type, fp.sha256))
 
             # Output the MD5 hash too if verbose mode is enabled.
             if out.verbose:
-                out.info('(fin) {}: {} -- [info] do not rely on MD5 fingerprints for server identification; it is insecure for this use case'.format(name, fp.md5))
+                out.info('(fin) {}: {} -- [info] do not rely on MD5 fingerprints for server identification; it is insecure for this use case'.format(fp_type, fp.md5))
 
     if not out.is_section_empty() and not is_json_output:
         out.head('# fingerprints')
@@ -422,7 +432,7 @@ def post_process_findings(banner: Optional[Banner], algs: Algorithms) -> List[st
     algorithm_recommendation_suppress_list = []
 
     # If the server is OpenSSH, and the diffie-hellman-group-exchange-sha256 key exchange was found with modulus size 2048, add a note regarding the bug that causes the server to support 2048-bit moduli no matter the configuration.
-    if (algs.ssh2kex is not None and 'diffie-hellman-group-exchange-sha256' in algs.ssh2kex.kex_algorithms and 'diffie-hellman-group-exchange-sha256' in algs.ssh2kex.dh_modulus_sizes() and algs.ssh2kex.dh_modulus_sizes()['diffie-hellman-group-exchange-sha256'][0] == 2048) and (banner is not None and banner.software is not None and banner.software.find('OpenSSH') != -1):
+    if (algs.ssh2kex is not None and 'diffie-hellman-group-exchange-sha256' in algs.ssh2kex.kex_algorithms and 'diffie-hellman-group-exchange-sha256' in algs.ssh2kex.dh_modulus_sizes() and algs.ssh2kex.dh_modulus_sizes()['diffie-hellman-group-exchange-sha256'] == 2048) and (banner is not None and banner.software is not None and banner.software.find('OpenSSH') != -1):
 
         # Ensure a list for notes exists.
         while len(SSH2_KexDB.ALGORITHMS['kex']['diffie-hellman-group-exchange-sha256']) < 4:
@@ -498,6 +508,8 @@ def output(out: OutputBuffer, aconf: AuditConf, banner: Optional[Banner], header
     cves = output_security(out, banner, client_audit, maxlen, aconf.json)
     # Filled in by output_algorithms() with unidentified algs.
     unknown_algorithms: List[str] = []
+
+    # SSHv1
     if pkm is not None:
         adb = SSH1_KexDB.ALGORITHMS
         ciphers = pkm.supported_ciphers
@@ -508,16 +520,19 @@ def output(out: OutputBuffer, aconf: AuditConf, banner: Optional[Banner], header
         program_retval = output_algorithms(out, title, adb, atype, ciphers, unknown_algorithms, aconf.json, program_retval, maxlen)
         title, atype = 'SSH1 authentication types', 'aut'
         program_retval = output_algorithms(out, title, adb, atype, auths, unknown_algorithms, aconf.json, program_retval, maxlen)
+
+    # SSHv2
     if kex is not None:
         adb = SSH2_KexDB.ALGORITHMS
         title, atype = 'key exchange algorithms', 'kex'
-        program_retval = output_algorithms(out, title, adb, atype, kex.kex_algorithms, unknown_algorithms, aconf.json, program_retval, maxlen, kex.dh_modulus_sizes())
+        program_retval = output_algorithms(out, title, adb, atype, kex.kex_algorithms, unknown_algorithms, aconf.json, program_retval, maxlen, dh_modulus_sizes=kex.dh_modulus_sizes())
         title, atype = 'host-key algorithms', 'key'
-        program_retval = output_algorithms(out, title, adb, atype, kex.key_algorithms, unknown_algorithms, aconf.json, program_retval, maxlen, kex.rsa_key_sizes())
+        program_retval = output_algorithms(out, title, adb, atype, kex.key_algorithms, unknown_algorithms, aconf.json, program_retval, maxlen, host_keys=kex.host_keys())
         title, atype = 'encryption algorithms (ciphers)', 'enc'
         program_retval = output_algorithms(out, title, adb, atype, kex.server.encryption, unknown_algorithms, aconf.json, program_retval, maxlen)
         title, atype = 'message authentication code algorithms', 'mac'
         program_retval = output_algorithms(out, title, adb, atype, kex.server.mac, unknown_algorithms, aconf.json, program_retval, maxlen)
+
     output_fingerprints(out, algs, aconf.json)
     perfect_config = output_recommendations(out, algs, algorithm_recommendation_suppress_list, software, aconf.json, maxlen)
     output_info(out, software, client_audit, not perfect_config, aconf.json)
@@ -830,10 +845,10 @@ def process_commandline(out: OutputBuffer, args: List[str], usage_cb: Callable[.
     if (aconf.policy_file is not None) and (aconf.make_policy is False):
 
         # First, see if this is a built-in policy name.  If not, assume a file path was provided, and try to load it from disk.
-        aconf.policy = Policy.load_builtin_policy(aconf.policy_file)
+        aconf.policy = Policy.load_builtin_policy(aconf.policy_file, json_output=aconf.json)
         if aconf.policy is None:
             try:
-                aconf.policy = Policy(policy_file=aconf.policy_file)
+                aconf.policy = Policy(policy_file=aconf.policy_file, json_output=aconf.json)
             except Exception as e:
                 out.fail("Error while loading policy file: %s: %s" % (str(e), traceback.format_exc()))
                 out.write()
@@ -885,28 +900,37 @@ def build_struct(target_host: str, banner: Optional['Banner'], cves: List[Dict[s
         res['compression'] = kex.server.compression
 
         res['kex'] = []
-        alg_sizes = kex.dh_modulus_sizes()
+        dh_alg_sizes = kex.dh_modulus_sizes()
         for algorithm in kex.kex_algorithms:
             entry: Any = {
                 'algorithm': algorithm,
             }
-            if algorithm in alg_sizes:
-                hostkey_size, ca_size = alg_sizes[algorithm]
+            if algorithm in dh_alg_sizes:
+                hostkey_size = dh_alg_sizes[algorithm]
                 entry['keysize'] = hostkey_size
-                if ca_size > 0:
-                    entry['casize'] = ca_size
             res['kex'].append(entry)
 
         res['key'] = []
-        alg_sizes = kex.rsa_key_sizes()
+        host_keys = kex.host_keys()
         for algorithm in kex.key_algorithms:
             entry = {
                 'algorithm': algorithm,
             }
-            if algorithm in alg_sizes:
-                hostkey_size, ca_size = alg_sizes[algorithm]
-                entry['keysize'] = hostkey_size
+            if algorithm in host_keys:
+                hostkey_info = host_keys[algorithm]
+                hostkey_size = cast(int, hostkey_info['hostkey_size'])
+
+                ca_type = ''
+                ca_size = 0
+                if 'ca_key_type' in hostkey_info:
+                    ca_type = cast(str, hostkey_info['ca_key_type'])
+                if 'ca_key_size' in hostkey_info:
+                    ca_size = cast(int, hostkey_info['ca_key_size'])
+
+                if algorithm in HostKeyTest.RSA_FAMILY or algorithm.startswith('ssh-rsa-cert-v0'):
+                    entry['keysize'] = hostkey_size
                 if ca_size > 0:
+                    entry['ca_algorithm'] = ca_type
                     entry['casize'] = ca_size
             res['key'].append(entry)
 
@@ -926,7 +950,7 @@ def build_struct(target_host: str, banner: Optional['Banner'], cves: List[Dict[s
             if host_keys[host_key_type] is None:
                 continue
 
-            fp = Fingerprint(host_keys[host_key_type])
+            fp = Fingerprint(cast(bytes, host_keys[host_key_type]['raw_hostkey_bytes']))
 
             # Skip over certificate host types (or we would return invalid fingerprints).
             if '-cert-' in host_key_type:
@@ -1041,7 +1065,7 @@ def audit(out: OutputBuffer, aconf: AuditConf, sshv: Optional[int] = None, print
         program_retval = output(out, aconf, banner, header, pkm=SSH1_PublicKeyMessage.parse(payload))
     elif sshv == 2:
         try:
-            kex = SSH2_Kex.parse(payload)
+            kex = SSH2_Kex.parse(out, payload)
         except Exception:
             out.fail("Failed to parse server's kex.  Stack trace:\n%s" % str(traceback.format_exc()))
             return exitcodes.CONNECTION_ERROR
diff --git a/src/ssh_audit/ssh_socket.py b/src/ssh_audit/ssh_socket.py
index 99ccbd2..5afa4ce 100644
--- a/src/ssh_audit/ssh_socket.py
+++ b/src/ssh_audit/ssh_socket.py
@@ -236,7 +236,7 @@ class SSH_Socket(ReadBuf, WriteBuf):
         self.__outputbuffer.d('KEX initialisation...', write_now=True)
 
         kexparty = SSH2_KexParty(ciphers, macs, compressions, languages)
-        kex = SSH2_Kex(os.urandom(16), key_exchanges, hostkeys, kexparty, kexparty, False, 0)
+        kex = SSH2_Kex(self.__outputbuffer, os.urandom(16), key_exchanges, hostkeys, kexparty, kexparty, False, 0)
 
         self.write_byte(Protocol.MSG_KEXINIT)
         kex.write(self)
diff --git a/test/docker/expected_results/openssh_5.6p1_custom_policy_test10.json b/test/docker/expected_results/openssh_5.6p1_custom_policy_test10.json
index b07940c..0a1e148 100644
--- a/test/docker/expected_results/openssh_5.6p1_custom_policy_test10.json
+++ b/test/docker/expected_results/openssh_5.6p1_custom_policy_test10.json
@@ -10,7 +10,7 @@
             "expected_required": [
                 "4096"
             ],
-            "mismatched_field": "RSA host key (ssh-rsa-cert-v01@openssh.com) sizes"
+            "mismatched_field": "Host key (ssh-rsa-cert-v01@openssh.com) sizes"
         },
         {
             "actual": [
@@ -22,7 +22,7 @@
             "expected_required": [
                 "4096"
             ],
-            "mismatched_field": "RSA CA key (ssh-rsa-cert-v01@openssh.com) sizes"
+            "mismatched_field": "CA signature size (ssh-rsa)"
         }
     ],
     "host": "localhost",
diff --git a/test/docker/expected_results/openssh_5.6p1_custom_policy_test10.txt b/test/docker/expected_results/openssh_5.6p1_custom_policy_test10.txt
index 7f8befc..425d463 100644
--- a/test/docker/expected_results/openssh_5.6p1_custom_policy_test10.txt
+++ b/test/docker/expected_results/openssh_5.6p1_custom_policy_test10.txt
@@ -1,13 +1,28 @@
+
+WARNING: this policy is using deprecated features.  Future versions of ssh-audit may remove support for them.  Re-generating the policy file is perhaps the most straight-forward way of resolving this issue.  Manually converting the 'hostkey_size_*', 'cakey_size_*', and 'dh_modulus_size_*' directives into the new format is another option.
+
+
+WARNING: this policy is using deprecated features.  Future versions of ssh-audit may remove support for them.  Re-generating the policy file is perhaps the most straight-forward way of resolving this issue.  Manually converting the 'hostkey_size_*', 'cakey_size_*', and 'dh_modulus_size_*' directives into the new format is another option.
+
+
+WARNING: this policy is using deprecated features.  Future versions of ssh-audit may remove support for them.  Re-generating the policy file is perhaps the most straight-forward way of resolving this issue.  Manually converting the 'hostkey_size_*', 'cakey_size_*', and 'dh_modulus_size_*' directives into the new format is another option.
+
+
+WARNING: this policy is using deprecated features.  Future versions of ssh-audit may remove support for them.  Re-generating the policy file is perhaps the most straight-forward way of resolving this issue.  Manually converting the 'hostkey_size_*', 'cakey_size_*', and 'dh_modulus_size_*' directives into the new format is another option.
+
+
+WARNING: this policy is using deprecated features.  Future versions of ssh-audit may remove support for them.  Re-generating the policy file is perhaps the most straight-forward way of resolving this issue.  Manually converting the 'hostkey_size_*', 'cakey_size_*', and 'dh_modulus_size_*' directives into the new format is another option.
+
 Host:   localhost:2222
 Policy: Docker poliicy: test10 (version 1)
 Result: ❌ Failed!
 
 Errors:
-  * RSA CA key (ssh-rsa-cert-v01@openssh.com) sizes did not match.
+  * CA signature size (ssh-rsa) did not match.
     - Expected: 4096
     - Actual:   1024
 
-  * RSA host key (ssh-rsa-cert-v01@openssh.com) sizes did not match.
+  * Host key (ssh-rsa-cert-v01@openssh.com) sizes did not match.
     - Expected: 4096
     - Actual:   3072
 
diff --git a/test/docker/expected_results/openssh_5.6p1_custom_policy_test7.txt b/test/docker/expected_results/openssh_5.6p1_custom_policy_test7.txt
index 4014b23..1d3af14 100644
--- a/test/docker/expected_results/openssh_5.6p1_custom_policy_test7.txt
+++ b/test/docker/expected_results/openssh_5.6p1_custom_policy_test7.txt
@@ -1,3 +1,18 @@
+
+WARNING: this policy is using deprecated features.  Future versions of ssh-audit may remove support for them.  Re-generating the policy file is perhaps the most straight-forward way of resolving this issue.  Manually converting the 'hostkey_size_*', 'cakey_size_*', and 'dh_modulus_size_*' directives into the new format is another option.
+
+
+WARNING: this policy is using deprecated features.  Future versions of ssh-audit may remove support for them.  Re-generating the policy file is perhaps the most straight-forward way of resolving this issue.  Manually converting the 'hostkey_size_*', 'cakey_size_*', and 'dh_modulus_size_*' directives into the new format is another option.
+
+
+WARNING: this policy is using deprecated features.  Future versions of ssh-audit may remove support for them.  Re-generating the policy file is perhaps the most straight-forward way of resolving this issue.  Manually converting the 'hostkey_size_*', 'cakey_size_*', and 'dh_modulus_size_*' directives into the new format is another option.
+
+
+WARNING: this policy is using deprecated features.  Future versions of ssh-audit may remove support for them.  Re-generating the policy file is perhaps the most straight-forward way of resolving this issue.  Manually converting the 'hostkey_size_*', 'cakey_size_*', and 'dh_modulus_size_*' directives into the new format is another option.
+
+
+WARNING: this policy is using deprecated features.  Future versions of ssh-audit may remove support for them.  Re-generating the policy file is perhaps the most straight-forward way of resolving this issue.  Manually converting the 'hostkey_size_*', 'cakey_size_*', and 'dh_modulus_size_*' directives into the new format is another option.
+
 Host:   localhost:2222
 Policy: Docker poliicy: test7 (version 1)
 Result: ✔ Passed
diff --git a/test/docker/expected_results/openssh_5.6p1_custom_policy_test8.json b/test/docker/expected_results/openssh_5.6p1_custom_policy_test8.json
index 391f224..e7f06a6 100644
--- a/test/docker/expected_results/openssh_5.6p1_custom_policy_test8.json
+++ b/test/docker/expected_results/openssh_5.6p1_custom_policy_test8.json
@@ -10,7 +10,7 @@
             "expected_required": [
                 "2048"
             ],
-            "mismatched_field": "RSA CA key (ssh-rsa-cert-v01@openssh.com) sizes"
+            "mismatched_field": "CA signature size (ssh-rsa)"
         }
     ],
     "host": "localhost",
diff --git a/test/docker/expected_results/openssh_5.6p1_custom_policy_test8.txt b/test/docker/expected_results/openssh_5.6p1_custom_policy_test8.txt
index 36dceba..05ab91d 100644
--- a/test/docker/expected_results/openssh_5.6p1_custom_policy_test8.txt
+++ b/test/docker/expected_results/openssh_5.6p1_custom_policy_test8.txt
@@ -1,9 +1,24 @@
+
+WARNING: this policy is using deprecated features.  Future versions of ssh-audit may remove support for them.  Re-generating the policy file is perhaps the most straight-forward way of resolving this issue.  Manually converting the 'hostkey_size_*', 'cakey_size_*', and 'dh_modulus_size_*' directives into the new format is another option.
+
+
+WARNING: this policy is using deprecated features.  Future versions of ssh-audit may remove support for them.  Re-generating the policy file is perhaps the most straight-forward way of resolving this issue.  Manually converting the 'hostkey_size_*', 'cakey_size_*', and 'dh_modulus_size_*' directives into the new format is another option.
+
+
+WARNING: this policy is using deprecated features.  Future versions of ssh-audit may remove support for them.  Re-generating the policy file is perhaps the most straight-forward way of resolving this issue.  Manually converting the 'hostkey_size_*', 'cakey_size_*', and 'dh_modulus_size_*' directives into the new format is another option.
+
+
+WARNING: this policy is using deprecated features.  Future versions of ssh-audit may remove support for them.  Re-generating the policy file is perhaps the most straight-forward way of resolving this issue.  Manually converting the 'hostkey_size_*', 'cakey_size_*', and 'dh_modulus_size_*' directives into the new format is another option.
+
+
+WARNING: this policy is using deprecated features.  Future versions of ssh-audit may remove support for them.  Re-generating the policy file is perhaps the most straight-forward way of resolving this issue.  Manually converting the 'hostkey_size_*', 'cakey_size_*', and 'dh_modulus_size_*' directives into the new format is another option.
+
 Host:   localhost:2222
 Policy: Docker poliicy: test8 (version 1)
 Result: ❌ Failed!
 
 Errors:
-  * RSA CA key (ssh-rsa-cert-v01@openssh.com) sizes did not match.
+  * CA signature size (ssh-rsa) did not match.
     - Expected: 2048
     - Actual:   1024
 
diff --git a/test/docker/expected_results/openssh_5.6p1_custom_policy_test9.json b/test/docker/expected_results/openssh_5.6p1_custom_policy_test9.json
index b32dfe6..51d1067 100644
--- a/test/docker/expected_results/openssh_5.6p1_custom_policy_test9.json
+++ b/test/docker/expected_results/openssh_5.6p1_custom_policy_test9.json
@@ -10,7 +10,7 @@
             "expected_required": [
                 "4096"
             ],
-            "mismatched_field": "RSA host key (ssh-rsa-cert-v01@openssh.com) sizes"
+            "mismatched_field": "Host key (ssh-rsa-cert-v01@openssh.com) sizes"
         }
     ],
     "host": "localhost",
diff --git a/test/docker/expected_results/openssh_5.6p1_custom_policy_test9.txt b/test/docker/expected_results/openssh_5.6p1_custom_policy_test9.txt
index fc91c9f..94060ab 100644
--- a/test/docker/expected_results/openssh_5.6p1_custom_policy_test9.txt
+++ b/test/docker/expected_results/openssh_5.6p1_custom_policy_test9.txt
@@ -1,9 +1,24 @@
+
+WARNING: this policy is using deprecated features.  Future versions of ssh-audit may remove support for them.  Re-generating the policy file is perhaps the most straight-forward way of resolving this issue.  Manually converting the 'hostkey_size_*', 'cakey_size_*', and 'dh_modulus_size_*' directives into the new format is another option.
+
+
+WARNING: this policy is using deprecated features.  Future versions of ssh-audit may remove support for them.  Re-generating the policy file is perhaps the most straight-forward way of resolving this issue.  Manually converting the 'hostkey_size_*', 'cakey_size_*', and 'dh_modulus_size_*' directives into the new format is another option.
+
+
+WARNING: this policy is using deprecated features.  Future versions of ssh-audit may remove support for them.  Re-generating the policy file is perhaps the most straight-forward way of resolving this issue.  Manually converting the 'hostkey_size_*', 'cakey_size_*', and 'dh_modulus_size_*' directives into the new format is another option.
+
+
+WARNING: this policy is using deprecated features.  Future versions of ssh-audit may remove support for them.  Re-generating the policy file is perhaps the most straight-forward way of resolving this issue.  Manually converting the 'hostkey_size_*', 'cakey_size_*', and 'dh_modulus_size_*' directives into the new format is another option.
+
+
+WARNING: this policy is using deprecated features.  Future versions of ssh-audit may remove support for them.  Re-generating the policy file is perhaps the most straight-forward way of resolving this issue.  Manually converting the 'hostkey_size_*', 'cakey_size_*', and 'dh_modulus_size_*' directives into the new format is another option.
+
 Host:   localhost:2222
 Policy: Docker poliicy: test9 (version 1)
 Result: ❌ Failed!
 
 Errors:
-  * RSA host key (ssh-rsa-cert-v01@openssh.com) sizes did not match.
+  * Host key (ssh-rsa-cert-v01@openssh.com) sizes did not match.
     - Expected: 4096
     - Actual:   3072
 
diff --git a/test/docker/expected_results/openssh_5.6p1_test2.json b/test/docker/expected_results/openssh_5.6p1_test2.json
index 2f19adb..ffe6e98 100644
--- a/test/docker/expected_results/openssh_5.6p1_test2.json
+++ b/test/docker/expected_results/openssh_5.6p1_test2.json
@@ -139,6 +139,7 @@
         },
         {
             "algorithm": "ssh-rsa-cert-v01@openssh.com",
+            "ca_algorithm": "ssh-rsa",
             "casize": 1024,
             "keysize": 1024
         }
diff --git a/test/docker/expected_results/openssh_5.6p1_test2.txt b/test/docker/expected_results/openssh_5.6p1_test2.txt
index 649e3c0..6b3b975 100644
--- a/test/docker/expected_results/openssh_5.6p1_test2.txt
+++ b/test/docker/expected_results/openssh_5.6p1_test2.txt
@@ -40,10 +40,11 @@
                                             `- [fail] using small 1024-bit modulus
                                             `- [info] available since OpenSSH 2.5.0, Dropbear SSH 0.28
                                             `- [info] deprecated in OpenSSH 8.8: https://www.openssh.com/txt/release-8.8
-(key) ssh-rsa-cert-v01@openssh.com (1024-bit cert/1024-bit CA) -- [fail] using broken SHA-1 hash algorithm
-                                                               `- [fail] using small 1024-bit modulus
-                                                               `- [info] available since OpenSSH 5.6
-                                                               `- [info] deprecated in OpenSSH 8.8: https://www.openssh.com/txt/release-8.8
+(key) ssh-rsa-cert-v01@openssh.com (1024-bit cert/1024-bit RSA CA) -- [fail] using broken SHA-1 hash algorithm
+                                                                   `- [fail] using small 1024-bit hostkey modulus
+                                                                   `- [fail] using small 1024-bit CA key modulus
+                                                                   `- [info] available since OpenSSH 5.6
+                                                                   `- [info] deprecated in OpenSSH 8.8: https://www.openssh.com/txt/release-8.8
 
 # encryption algorithms (ciphers)
 (enc) aes128-ctr                            -- [info] available since OpenSSH 3.7, Dropbear SSH 0.52
diff --git a/test/docker/expected_results/openssh_5.6p1_test3.json b/test/docker/expected_results/openssh_5.6p1_test3.json
index 4cf7456..b4f01af 100644
--- a/test/docker/expected_results/openssh_5.6p1_test3.json
+++ b/test/docker/expected_results/openssh_5.6p1_test3.json
@@ -139,6 +139,7 @@
         },
         {
             "algorithm": "ssh-rsa-cert-v01@openssh.com",
+            "ca_algorithm": "ssh-rsa",
             "casize": 3072,
             "keysize": 1024
         }
diff --git a/test/docker/expected_results/openssh_5.6p1_test3.txt b/test/docker/expected_results/openssh_5.6p1_test3.txt
index ce2edb2..991c502 100644
--- a/test/docker/expected_results/openssh_5.6p1_test3.txt
+++ b/test/docker/expected_results/openssh_5.6p1_test3.txt
@@ -40,10 +40,10 @@
                                             `- [fail] using small 1024-bit modulus
                                             `- [info] available since OpenSSH 2.5.0, Dropbear SSH 0.28
                                             `- [info] deprecated in OpenSSH 8.8: https://www.openssh.com/txt/release-8.8
-(key) ssh-rsa-cert-v01@openssh.com (1024-bit cert/3072-bit CA) -- [fail] using broken SHA-1 hash algorithm
-                                                               `- [fail] using small 1024-bit modulus
-                                                               `- [info] available since OpenSSH 5.6
-                                                               `- [info] deprecated in OpenSSH 8.8: https://www.openssh.com/txt/release-8.8
+(key) ssh-rsa-cert-v01@openssh.com (1024-bit cert/3072-bit RSA CA) -- [fail] using broken SHA-1 hash algorithm
+                                                                   `- [fail] using small 1024-bit hostkey modulus
+                                                                   `- [info] available since OpenSSH 5.6
+                                                                   `- [info] deprecated in OpenSSH 8.8: https://www.openssh.com/txt/release-8.8
 
 # encryption algorithms (ciphers)
 (enc) aes128-ctr                            -- [info] available since OpenSSH 3.7, Dropbear SSH 0.52
diff --git a/test/docker/expected_results/openssh_5.6p1_test4.json b/test/docker/expected_results/openssh_5.6p1_test4.json
index bfc84d8..074f2b1 100644
--- a/test/docker/expected_results/openssh_5.6p1_test4.json
+++ b/test/docker/expected_results/openssh_5.6p1_test4.json
@@ -139,6 +139,7 @@
         },
         {
             "algorithm": "ssh-rsa-cert-v01@openssh.com",
+            "ca_algorithm": "ssh-rsa",
             "casize": 1024,
             "keysize": 3072
         }
diff --git a/test/docker/expected_results/openssh_5.6p1_test4.txt b/test/docker/expected_results/openssh_5.6p1_test4.txt
index c362c18..2fb3e19 100644
--- a/test/docker/expected_results/openssh_5.6p1_test4.txt
+++ b/test/docker/expected_results/openssh_5.6p1_test4.txt
@@ -39,10 +39,10 @@
 (key) ssh-rsa (3072-bit)                    -- [fail] using broken SHA-1 hash algorithm
                                             `- [info] available since OpenSSH 2.5.0, Dropbear SSH 0.28
                                             `- [info] deprecated in OpenSSH 8.8: https://www.openssh.com/txt/release-8.8
-(key) ssh-rsa-cert-v01@openssh.com (3072-bit cert/1024-bit CA) -- [fail] using broken SHA-1 hash algorithm
-                                                               `- [fail] using small 1024-bit modulus
-                                                               `- [info] available since OpenSSH 5.6
-                                                               `- [info] deprecated in OpenSSH 8.8: https://www.openssh.com/txt/release-8.8
+(key) ssh-rsa-cert-v01@openssh.com (3072-bit cert/1024-bit RSA CA) -- [fail] using broken SHA-1 hash algorithm
+                                                                   `- [fail] using small 1024-bit CA key modulus
+                                                                   `- [info] available since OpenSSH 5.6
+                                                                   `- [info] deprecated in OpenSSH 8.8: https://www.openssh.com/txt/release-8.8
 
 # encryption algorithms (ciphers)
 (enc) aes128-ctr                            -- [info] available since OpenSSH 3.7, Dropbear SSH 0.52
diff --git a/test/docker/expected_results/openssh_5.6p1_test5.json b/test/docker/expected_results/openssh_5.6p1_test5.json
index c950633..a645f0e 100644
--- a/test/docker/expected_results/openssh_5.6p1_test5.json
+++ b/test/docker/expected_results/openssh_5.6p1_test5.json
@@ -139,6 +139,7 @@
         },
         {
             "algorithm": "ssh-rsa-cert-v01@openssh.com",
+            "ca_algorithm": "ssh-rsa",
             "casize": 3072,
             "keysize": 3072
         }
diff --git a/test/docker/expected_results/openssh_5.6p1_test5.txt b/test/docker/expected_results/openssh_5.6p1_test5.txt
index 4d388d1..b9e7cd7 100644
--- a/test/docker/expected_results/openssh_5.6p1_test5.txt
+++ b/test/docker/expected_results/openssh_5.6p1_test5.txt
@@ -39,9 +39,9 @@
 (key) ssh-rsa (3072-bit)                    -- [fail] using broken SHA-1 hash algorithm
                                             `- [info] available since OpenSSH 2.5.0, Dropbear SSH 0.28
                                             `- [info] deprecated in OpenSSH 8.8: https://www.openssh.com/txt/release-8.8
-(key) ssh-rsa-cert-v01@openssh.com (3072-bit cert/3072-bit CA) -- [fail] using broken SHA-1 hash algorithm
-                                                               `- [info] available since OpenSSH 5.6
-                                                               `- [info] deprecated in OpenSSH 8.8: https://www.openssh.com/txt/release-8.8
+(key) ssh-rsa-cert-v01@openssh.com (3072-bit cert/3072-bit RSA CA) -- [fail] using broken SHA-1 hash algorithm
+                                                                   `- [info] available since OpenSSH 5.6
+                                                                   `- [info] deprecated in OpenSSH 8.8: https://www.openssh.com/txt/release-8.8
 
 # encryption algorithms (ciphers)
 (enc) aes128-ctr                            -- [info] available since OpenSSH 3.7, Dropbear SSH 0.52
diff --git a/test/docker/expected_results/openssh_8.0p1_custom_policy_test11.txt b/test/docker/expected_results/openssh_8.0p1_custom_policy_test11.txt
index 024bcb9..0ac0671 100644
--- a/test/docker/expected_results/openssh_8.0p1_custom_policy_test11.txt
+++ b/test/docker/expected_results/openssh_8.0p1_custom_policy_test11.txt
@@ -1,3 +1,12 @@
+
+WARNING: this policy is using deprecated features.  Future versions of ssh-audit may remove support for them.  Re-generating the policy file is perhaps the most straight-forward way of resolving this issue.  Manually converting the 'hostkey_size_*', 'cakey_size_*', and 'dh_modulus_size_*' directives into the new format is another option.
+
+
+WARNING: this policy is using deprecated features.  Future versions of ssh-audit may remove support for them.  Re-generating the policy file is perhaps the most straight-forward way of resolving this issue.  Manually converting the 'hostkey_size_*', 'cakey_size_*', and 'dh_modulus_size_*' directives into the new format is another option.
+
+
+WARNING: this policy is using deprecated features.  Future versions of ssh-audit may remove support for them.  Re-generating the policy file is perhaps the most straight-forward way of resolving this issue.  Manually converting the 'hostkey_size_*', 'cakey_size_*', and 'dh_modulus_size_*' directives into the new format is another option.
+
 Host:   localhost:2222
 Policy: Docker policy: test11 (version 1)
 Result: ✔ Passed
diff --git a/test/docker/expected_results/openssh_8.0p1_custom_policy_test12.json b/test/docker/expected_results/openssh_8.0p1_custom_policy_test12.json
index 2a21591..8ddcf39 100644
--- a/test/docker/expected_results/openssh_8.0p1_custom_policy_test12.json
+++ b/test/docker/expected_results/openssh_8.0p1_custom_policy_test12.json
@@ -10,7 +10,7 @@
             "expected_required": [
                 "4096"
             ],
-            "mismatched_field": "RSA host key (rsa-sha2-256) sizes"
+            "mismatched_field": "Host key (rsa-sha2-256) sizes"
         },
         {
             "actual": [
@@ -22,7 +22,7 @@
             "expected_required": [
                 "4096"
             ],
-            "mismatched_field": "RSA host key (rsa-sha2-512) sizes"
+            "mismatched_field": "Host key (rsa-sha2-512) sizes"
         },
         {
             "actual": [
@@ -34,7 +34,7 @@
             "expected_required": [
                 "4096"
             ],
-            "mismatched_field": "RSA host key (ssh-rsa) sizes"
+            "mismatched_field": "Host key (ssh-rsa) sizes"
         }
     ],
     "host": "localhost",
diff --git a/test/docker/expected_results/openssh_8.0p1_custom_policy_test12.txt b/test/docker/expected_results/openssh_8.0p1_custom_policy_test12.txt
index 6fb0561..de615e0 100644
--- a/test/docker/expected_results/openssh_8.0p1_custom_policy_test12.txt
+++ b/test/docker/expected_results/openssh_8.0p1_custom_policy_test12.txt
@@ -1,17 +1,26 @@
+
+WARNING: this policy is using deprecated features.  Future versions of ssh-audit may remove support for them.  Re-generating the policy file is perhaps the most straight-forward way of resolving this issue.  Manually converting the 'hostkey_size_*', 'cakey_size_*', and 'dh_modulus_size_*' directives into the new format is another option.
+
+
+WARNING: this policy is using deprecated features.  Future versions of ssh-audit may remove support for them.  Re-generating the policy file is perhaps the most straight-forward way of resolving this issue.  Manually converting the 'hostkey_size_*', 'cakey_size_*', and 'dh_modulus_size_*' directives into the new format is another option.
+
+
+WARNING: this policy is using deprecated features.  Future versions of ssh-audit may remove support for them.  Re-generating the policy file is perhaps the most straight-forward way of resolving this issue.  Manually converting the 'hostkey_size_*', 'cakey_size_*', and 'dh_modulus_size_*' directives into the new format is another option.
+
 Host:   localhost:2222
 Policy: Docker policy: test12 (version 1)
 Result: ❌ Failed!
 
 Errors:
-  * RSA host key (rsa-sha2-256) sizes did not match.
+  * Host key (rsa-sha2-256) sizes did not match.
     - Expected: 4096
     - Actual:   3072
 
-  * RSA host key (rsa-sha2-512) sizes did not match.
+  * Host key (rsa-sha2-512) sizes did not match.
     - Expected: 4096
     - Actual:   3072
 
-  * RSA host key (ssh-rsa) sizes did not match.
+  * Host key (ssh-rsa) sizes did not match.
     - Expected: 4096
     - Actual:   3072
 
diff --git a/test/docker/expected_results/openssh_8.0p1_custom_policy_test13.txt b/test/docker/expected_results/openssh_8.0p1_custom_policy_test13.txt
index b8b4b25..7734d88 100644
--- a/test/docker/expected_results/openssh_8.0p1_custom_policy_test13.txt
+++ b/test/docker/expected_results/openssh_8.0p1_custom_policy_test13.txt
@@ -1,3 +1,15 @@
+
+WARNING: this policy is using deprecated features.  Future versions of ssh-audit may remove support for them.  Re-generating the policy file is perhaps the most straight-forward way of resolving this issue.  Manually converting the 'hostkey_size_*', 'cakey_size_*', and 'dh_modulus_size_*' directives into the new format is another option.
+
+
+WARNING: this policy is using deprecated features.  Future versions of ssh-audit may remove support for them.  Re-generating the policy file is perhaps the most straight-forward way of resolving this issue.  Manually converting the 'hostkey_size_*', 'cakey_size_*', and 'dh_modulus_size_*' directives into the new format is another option.
+
+
+WARNING: this policy is using deprecated features.  Future versions of ssh-audit may remove support for them.  Re-generating the policy file is perhaps the most straight-forward way of resolving this issue.  Manually converting the 'hostkey_size_*', 'cakey_size_*', and 'dh_modulus_size_*' directives into the new format is another option.
+
+
+WARNING: this policy is using deprecated features.  Future versions of ssh-audit may remove support for them.  Re-generating the policy file is perhaps the most straight-forward way of resolving this issue.  Manually converting the 'hostkey_size_*', 'cakey_size_*', and 'dh_modulus_size_*' directives into the new format is another option.
+
 Host:   localhost:2222
 Policy: Docker policy: test13 (version 1)
 Result: ✔ Passed
diff --git a/test/docker/expected_results/openssh_8.0p1_custom_policy_test14.txt b/test/docker/expected_results/openssh_8.0p1_custom_policy_test14.txt
index 2bb59fb..5d9bdbf 100644
--- a/test/docker/expected_results/openssh_8.0p1_custom_policy_test14.txt
+++ b/test/docker/expected_results/openssh_8.0p1_custom_policy_test14.txt
@@ -1,3 +1,15 @@
+
+WARNING: this policy is using deprecated features.  Future versions of ssh-audit may remove support for them.  Re-generating the policy file is perhaps the most straight-forward way of resolving this issue.  Manually converting the 'hostkey_size_*', 'cakey_size_*', and 'dh_modulus_size_*' directives into the new format is another option.
+
+
+WARNING: this policy is using deprecated features.  Future versions of ssh-audit may remove support for them.  Re-generating the policy file is perhaps the most straight-forward way of resolving this issue.  Manually converting the 'hostkey_size_*', 'cakey_size_*', and 'dh_modulus_size_*' directives into the new format is another option.
+
+
+WARNING: this policy is using deprecated features.  Future versions of ssh-audit may remove support for them.  Re-generating the policy file is perhaps the most straight-forward way of resolving this issue.  Manually converting the 'hostkey_size_*', 'cakey_size_*', and 'dh_modulus_size_*' directives into the new format is another option.
+
+
+WARNING: this policy is using deprecated features.  Future versions of ssh-audit may remove support for them.  Re-generating the policy file is perhaps the most straight-forward way of resolving this issue.  Manually converting the 'hostkey_size_*', 'cakey_size_*', and 'dh_modulus_size_*' directives into the new format is another option.
+
 Host:   localhost:2222
 Policy: Docker policy: test14 (version 1)
 Result: ❌ Failed!
diff --git a/test/docker/expected_results/openssh_8.0p1_test2.json b/test/docker/expected_results/openssh_8.0p1_test2.json
index 737d044..7f68635 100644
--- a/test/docker/expected_results/openssh_8.0p1_test2.json
+++ b/test/docker/expected_results/openssh_8.0p1_test2.json
@@ -92,7 +92,9 @@
             "algorithm": "ssh-ed25519"
         },
         {
-            "algorithm": "ssh-ed25519-cert-v01@openssh.com"
+            "algorithm": "ssh-ed25519-cert-v01@openssh.com",
+            "ca_algorithm": "ssh-ed25519",
+            "casize": 256
         }
     ],
     "mac": [
diff --git a/test/docker/expected_results/openssh_8.0p1_test2.txt b/test/docker/expected_results/openssh_8.0p1_test2.txt
index 8250da6..b049d90 100644
--- a/test/docker/expected_results/openssh_8.0p1_test2.txt
+++ b/test/docker/expected_results/openssh_8.0p1_test2.txt
@@ -34,7 +34,7 @@
 
 # host-key algorithms
 (key) ssh-ed25519                           -- [info] available since OpenSSH 6.5
-(key) ssh-ed25519-cert-v01@openssh.com      -- [info] available since OpenSSH 6.5
+(key) ssh-ed25519-cert-v01@openssh.com (256-bit cert/256-bit ssh-ed25519 CA) -- [info] available since OpenSSH 6.5
 
 # encryption algorithms (ciphers)
 (enc) chacha20-poly1305@openssh.com         -- [info] available since OpenSSH 6.5
diff --git a/test/test_build_struct.py b/test/test_build_struct.py
index ce00142..e16baac 100644
--- a/test/test_build_struct.py
+++ b/test/test_build_struct.py
@@ -1,6 +1,7 @@
 import os
 import pytest
 
+from ssh_audit.outputbuffer import OutputBuffer
 from ssh_audit.ssh2_kex import SSH2_Kex
 from ssh_audit.ssh2_kexparty import SSH2_KexParty
 
@@ -13,7 +14,7 @@ def kex(ssh_audit):
     enc, mac, compression, languages = [], [], ['none'], []
     srv = SSH2_KexParty(enc, mac, compression, languages)
     cookie = os.urandom(16)
-    kex = SSH2_Kex(cookie, kex_algs, key_algs, cli, srv, 0)
+    kex = SSH2_Kex(OutputBuffer, cookie, kex_algs, key_algs, cli, srv, 0)
     return kex
 
 
@@ -25,15 +26,15 @@ def test_prevent_runtime_error_regression(ssh_audit, kex):
     keys, and an error occurred when iterating and modifying them at the
     same time.
     """
-    kex.set_host_key("ssh-rsa", b"\x00\x00\x00\x07ssh-rsa\x00\x00\x00")
-    kex.set_host_key("ssh-rsa1", b"\x00\x00\x00\x07ssh-rsa\x00\x00\x00")
-    kex.set_host_key("ssh-rsa2", b"\x00\x00\x00\x07ssh-rsa\x00\x00\x00")
-    kex.set_host_key("ssh-rsa3", b"\x00\x00\x00\x07ssh-rsa\x00\x00\x00")
-    kex.set_host_key("ssh-rsa4", b"\x00\x00\x00\x07ssh-rsa\x00\x00\x00")
-    kex.set_host_key("ssh-rsa5", b"\x00\x00\x00\x07ssh-rsa\x00\x00\x00")
-    kex.set_host_key("ssh-rsa6", b"\x00\x00\x00\x07ssh-rsa\x00\x00\x00")
-    kex.set_host_key("ssh-rsa7", b"\x00\x00\x00\x07ssh-rsa\x00\x00\x00")
-    kex.set_host_key("ssh-rsa8", b"\x00\x00\x00\x07ssh-rsa\x00\x00\x00")
+    kex.set_host_key("ssh-rsa", b"\x00\x00\x00\x07ssh-rsa\x00\x00\x00", 1024, '', 0)
+    kex.set_host_key("ssh-rsa1", b"\x00\x00\x00\x07ssh-rsa\x00\x00\x00", 1024, '', 0)
+    kex.set_host_key("ssh-rsa2", b"\x00\x00\x00\x07ssh-rsa\x00\x00\x00", 1024, '', 0)
+    kex.set_host_key("ssh-rsa3", b"\x00\x00\x00\x07ssh-rsa\x00\x00\x00", 1024, '', 0)
+    kex.set_host_key("ssh-rsa4", b"\x00\x00\x00\x07ssh-rsa\x00\x00\x00", 1024, '', 0)
+    kex.set_host_key("ssh-rsa5", b"\x00\x00\x00\x07ssh-rsa\x00\x00\x00", 1024, '', 0)
+    kex.set_host_key("ssh-rsa6", b"\x00\x00\x00\x07ssh-rsa\x00\x00\x00", 1024, '', 0)
+    kex.set_host_key("ssh-rsa7", b"\x00\x00\x00\x07ssh-rsa\x00\x00\x00", 1024, '', 0)
+    kex.set_host_key("ssh-rsa8", b"\x00\x00\x00\x07ssh-rsa\x00\x00\x00", 1024, '', 0)
 
     rv = ssh_audit.build_struct('localhost', None, [], kex=kex)
 
diff --git a/test/test_policy.py b/test/test_policy.py
index a008b81..f6a0af9 100644
--- a/test/test_policy.py
+++ b/test/test_policy.py
@@ -2,6 +2,7 @@ import hashlib
 import pytest
 from datetime import date
 
+from ssh_audit.outputbuffer import OutputBuffer
 from ssh_audit.policy import Policy
 from ssh_audit.ssh2_kex import SSH2_Kex
 from ssh_audit.writebuf import WriteBuf
@@ -10,6 +11,7 @@ from ssh_audit.writebuf import WriteBuf
 class TestPolicy:
     @pytest.fixture(autouse=True)
     def init(self, ssh_audit):
+        self.OutputBuffer = OutputBuffer
         self.Policy = Policy
         self.wbuf = WriteBuf
         self.ssh2_kex = SSH2_Kex
@@ -32,7 +34,7 @@ class TestPolicy:
         w.write_list([''])
         w.write_byte(False)
         w.write_int(0)
-        return self.ssh2_kex.parse(w.write_flush())
+        return self.ssh2_kex.parse(self.OutputBuffer, w.write_flush())
 
 
     def test_builtin_policy_consistency(self):
diff --git a/test/test_ssh2.py b/test/test_ssh2.py
index d0e5ba1..4674812 100644
--- a/test/test_ssh2.py
+++ b/test/test_ssh2.py
@@ -79,7 +79,7 @@ class TestSSH2:
         return w.write_flush()
 
     def test_kex_read(self):
-        kex = self.ssh2_kex.parse(self._kex_payload())
+        kex = self.ssh2_kex.parse(self.OutputBuffer, self._kex_payload())
         assert kex is not None
         assert kex.cookie == b'\x00\x11\x22\x33\x44\x55\x66\x77\x88\x99\xaa\xbb\xcc\xdd\xee\xff'
         assert kex.kex_algorithms == ['bogus_kex1', 'bogus_kex2']
@@ -105,7 +105,7 @@ class TestSSH2:
         srv = self.ssh2_kexparty(enc, mac, compression, languages)
         if cookie is None:
             cookie = os.urandom(16)
-        kex = self.ssh2_kex(cookie, kex_algs, key_algs, cli, srv, 0)
+        kex = self.ssh2_kex(self.OutputBuffer, cookie, kex_algs, key_algs, cli, srv, 0)
         return kex
 
     def _get_kex_variat1(self):
@@ -149,7 +149,7 @@ class TestSSH2:
 
     def test_key_payload(self):
         kex1 = self._get_kex_variat1()
-        kex2 = self.ssh2_kex.parse(self._kex_payload())
+        kex2 = self.ssh2_kex.parse(self.OutputBuffer, self._kex_payload())
         assert kex1.payload == kex2.payload
 
     def test_ssh2_server_simple(self, output_spy, virtual_socket):