Add support for SSH certificates using ecdsa-sk or ed25519-sk public keys

Fixes #796

plugins/module_utils/openssh/certificate.py

@@ -5,6 +5,7 @@
 # SPDX-License-Identifier: GPL-3.0-or-later
 
 from __future__ import absolute_import, division, print_function
+
 __metaclass__ = type
 
 # Protocol References
@@ -14,6 +15,7 @@ __metaclass__ = type
 # https://datatracker.ietf.org/doc/html/rfc5656
 # https://datatracker.ietf.org/doc/html/rfc8032
 # https://cvsweb.openbsd.org/src/usr.bin/ssh/PROTOCOL.certkeys?annotate=HEAD
+# https://cvsweb.openbsd.org/src/usr.bin/ssh/PROTOCOL.u2f?annotate=HEAD
 #
 # Inspired by:
 # ------------
@@ -52,8 +54,13 @@ _SSH_TYPE_STRINGS = {
     'ecdsa-nistp384': b"ecdsa-sha2-nistp384",
     'ecdsa-nistp521': b"ecdsa-sha2-nistp521",
     'ed25519': b"ssh-ed25519",
+    # FIDO2 hardware keys
+    'ecdsa-sk': b"sk-ecdsa-sha2-nistp256",
+    'ed25519-sk': b"sk-ssh-ed25519",
 }
 _CERT_SUFFIX_V01 = b"-cert-v01@openssh.com"
+_SK_SUFFIX = b"@openssh.com"
+_SK_PREFIX = b"sk-"
 
 # See https://datatracker.ietf.org/doc/html/rfc5656#section-6.1
 _ECDSA_CURVE_IDENTIFIERS = {
@@ -69,7 +76,6 @@ _ECDSA_CURVE_IDENTIFIERS_LOOKUP = {
 
 _USE_TIMEZONE = sys.version_info >= (3, 6)
 
-
 _ALWAYS = _add_or_remove_timezone(datetime(1970, 1, 1), with_timezone=_USE_TIMEZONE)
 _FOREVER = datetime(9999, 12, 31, 23, 59, 59, 999999, _UTC) if _USE_TIMEZONE else datetime.max
 
@@ -145,7 +151,8 @@ class OpensshCertificateTimeParameters(object):
             elif dt == _FOREVER:
                 result = 'forever'
             else:
-                result = dt.isoformat().replace('+00:00', '') if date_format == 'human_readable' else dt.strftime("%Y%m%d%H%M%S")
+                result = dt.isoformat().replace('+00:00', '') if date_format == 'human_readable' else dt.strftime(
+                    "%Y%m%d%H%M%S")
         elif date_format == 'timestamp':
             td = dt - _ALWAYS
             result = int((td.microseconds + (td.seconds + td.days * 24 * 3600) * 10 ** 6) / 10 ** 6)
@@ -196,7 +203,8 @@ class OpensshCertificateTimeParameters(object):
         else:
             for time_format in ("%Y-%m-%d", "%Y-%m-%d %H:%M:%S", "%Y-%m-%dT%H:%M:%S"):
                 try:
-                    result = _add_or_remove_timezone(datetime.strptime(time_string, time_format), with_timezone=_USE_TIMEZONE)
+                    result = _add_or_remove_timezone(datetime.strptime(time_string, time_format),
+                                                     with_timezone=_USE_TIMEZONE)
                 except ValueError:
                     pass
             if result is None:
@@ -279,6 +287,7 @@ class OpensshCertificateOption(object):
 @six.add_metaclass(abc.ABCMeta)
 class OpensshCertificateInfo:
     """Encapsulates all certificate information which is signed by a CA key"""
+
     def __init__(self,
                  nonce=None,
                  serial=None,
@@ -304,6 +313,7 @@ class OpensshCertificateInfo:
         self.signing_key = signing_key
 
         self.type_string = None
+        self.public_key_type_string = None
 
     @property
     def cert_type(self):
@@ -326,8 +336,17 @@ class OpensshCertificateInfo:
     def signing_key_fingerprint(self):
         return fingerprint(self.signing_key)
 
-    @abc.abstractmethod
     def public_key_fingerprint(self):
+        if self.public_key_type_string is None:
+            return b''
+        writer = _OpensshWriter()
+
+        writer.string(self.public_key_type_string)
+        self.write_public_key_params(writer)
+        return fingerprint(writer.bytes())
+
+    @abc.abstractmethod
+    def write_public_key_params(self, writer):
         pass
 
     @abc.abstractmethod
@@ -339,21 +358,18 @@ class OpensshRSACertificateInfo(OpensshCertificateInfo):
     def __init__(self, e=None, n=None, **kwargs):
         super(OpensshRSACertificateInfo, self).__init__(**kwargs)
         self.type_string = _SSH_TYPE_STRINGS['rsa'] + _CERT_SUFFIX_V01
+        self.public_key_type_string = _SSH_TYPE_STRINGS['rsa']
         self.e = e
         self.n = n
 
     # See https://datatracker.ietf.org/doc/html/rfc4253#section-6.6
-    def public_key_fingerprint(self):
+    def write_public_key_params(self, writer):
         if any([self.e is None, self.n is None]):
-            return b''
+            return
 
-        writer = _OpensshWriter()
-        writer.string(_SSH_TYPE_STRINGS['rsa'])
         writer.mpint(self.e)
         writer.mpint(self.n)
 
-        return fingerprint(writer.bytes())
-
     def parse_public_numbers(self, parser):
         self.e = parser.mpint()
         self.n = parser.mpint()
@@ -363,25 +379,22 @@ class OpensshDSACertificateInfo(OpensshCertificateInfo):
     def __init__(self, p=None, q=None, g=None, y=None, **kwargs):
         super(OpensshDSACertificateInfo, self).__init__(**kwargs)
         self.type_string = _SSH_TYPE_STRINGS['dsa'] + _CERT_SUFFIX_V01
+        self.public_key_type_string = _SSH_TYPE_STRINGS['dsa']
         self.p = p
         self.q = q
         self.g = g
         self.y = y
 
     # See https://datatracker.ietf.org/doc/html/rfc4253#section-6.6
-    def public_key_fingerprint(self):
+    def write_public_key_params(self, writer):
         if any([self.p is None, self.q is None, self.g is None, self.y is None]):
-            return b''
+            return
 
-        writer = _OpensshWriter()
-        writer.string(_SSH_TYPE_STRINGS['dsa'])
         writer.mpint(self.p)
         writer.mpint(self.q)
         writer.mpint(self.g)
         writer.mpint(self.y)
 
-        return fingerprint(writer.bytes())
-
     def parse_public_numbers(self, parser):
         self.p = parser.mpint()
         self.q = parser.mpint()
@@ -406,6 +419,7 @@ class OpensshECDSACertificateInfo(OpensshCertificateInfo):
     def curve(self, curve):
         if curve in _ECDSA_CURVE_IDENTIFIERS.values():
             self._curve = curve
+            self.public_key_type_string = _SSH_TYPE_STRINGS[_ECDSA_CURVE_IDENTIFIERS_LOOKUP[curve]]
             self.type_string = _SSH_TYPE_STRINGS[_ECDSA_CURVE_IDENTIFIERS_LOOKUP[curve]] + _CERT_SUFFIX_V01
         else:
             raise ValueError(
@@ -413,17 +427,13 @@ class OpensshECDSACertificateInfo(OpensshCertificateInfo):
             )
 
     # See https://datatracker.ietf.org/doc/html/rfc4253#section-6.6
-    def public_key_fingerprint(self):
+    def write_public_key_params(self, writer):
         if any([self.curve is None, self.public_key is None]):
-            return b''
+            return
 
-        writer = _OpensshWriter()
-        writer.string(_SSH_TYPE_STRINGS[_ECDSA_CURVE_IDENTIFIERS_LOOKUP[self.curve]])
         writer.string(self.curve)
         writer.string(self.public_key)
 
-        return fingerprint(writer.bytes())
-
     def parse_public_numbers(self, parser):
         self.curve = parser.string()
         self.public_key = parser.string()
@@ -433,25 +443,74 @@ class OpensshED25519CertificateInfo(OpensshCertificateInfo):
     def __init__(self, pk=None, **kwargs):
         super(OpensshED25519CertificateInfo, self).__init__(**kwargs)
         self.type_string = _SSH_TYPE_STRINGS['ed25519'] + _CERT_SUFFIX_V01
+        self.public_key_type_string = _SSH_TYPE_STRINGS['ed25519']
         self.pk = pk
 
-    def public_key_fingerprint(self):
+    def write_public_key_params(self, writer):
         if self.pk is None:
-            return b''
+            return
-
-        writer = _OpensshWriter()
-        writer.string(_SSH_TYPE_STRINGS['ed25519'])
         writer.string(self.pk)
 
-        return fingerprint(writer.bytes())
-
     def parse_public_numbers(self, parser):
         self.pk = parser.string()
 
 
+class OpensshSKECDSACertificateInfo(OpensshECDSACertificateInfo):
+    def __init__(self, application=b"ssh:", curve=None, **kwargs):
+        if curve is None:
+            curve = b'nistp256'
+        super(OpensshSKECDSACertificateInfo, self).__init__(curve=curve, **kwargs)
+
+        self.type_string = _SSH_TYPE_STRINGS['ecdsa-sk'] + _CERT_SUFFIX_V01
+        self.public_key_type_string = _SSH_TYPE_STRINGS['ecdsa-sk'] + _SK_SUFFIX
+        self.application = application
+
+    def write_public_key_params(self, writer):
+        if self.application is None:
+            return
+
+        super(OpensshSKECDSACertificateInfo, self).write_public_key_params(writer)
+
+        writer.string(self.application)
+
+    def parse_public_numbers(self, parser):
+        super(OpensshSKECDSACertificateInfo, self).parse_public_numbers(parser)
+
+        self.application = parser.string()
+
+    @OpensshECDSACertificateInfo.curve.setter
+    def curve(self, curve):
+        if curve != b'nistp256':
+            raise ValueError(
+                "ecdsa-sk only supports curve nistp256"
+            )
+        self._curve = curve
+
+class OpensshSKED25519CertificateInfo(OpensshED25519CertificateInfo):
+    def __init__(self, application=b"ssh:", **kwargs):
+        super(OpensshSKED25519CertificateInfo, self).__init__(**kwargs)
+        self.type_string = _SSH_TYPE_STRINGS['ed25519-sk'] + _CERT_SUFFIX_V01
+        self.public_key_type_string = _SSH_TYPE_STRINGS['ed25519-sk'] + _SK_SUFFIX
+        self.application = application
+
+    def write_public_key_params(self, writer):
+        if self.application is None:
+            return
+
+        super(OpensshSKED25519CertificateInfo, self).write_public_key_params(writer)
+
+        writer.string(self.application)
+
+    def parse_public_numbers(self, parser):
+        super(OpensshSKED25519CertificateInfo, self).parse_public_numbers(parser)
+
+        self.application = parser.string()
+
+
 # See https://cvsweb.openbsd.org/src/usr.bin/ssh/PROTOCOL.certkeys?annotate=HEAD
 class OpensshCertificate(object):
     """Encapsulates a formatted OpenSSH certificate including signature and signing key"""
+
     def __init__(self, cert_info, signature):
 
         self._cert_info = cert_info
@@ -635,10 +694,14 @@ def get_cert_info_object(key_type):
         cert_info = OpensshRSACertificateInfo()
     elif key_type == 'dsa':
         cert_info = OpensshDSACertificateInfo()
-    elif key_type in ('ecdsa-nistp256', 'ecdsa-nistp384', 'ecdsa-nistp521'):
+    elif key_type in _ECDSA_CURVE_IDENTIFIERS:
         cert_info = OpensshECDSACertificateInfo()
     elif key_type == 'ed25519':
         cert_info = OpensshED25519CertificateInfo()
+    elif key_type == 'ecdsa-sk':
+        cert_info = OpensshSKECDSACertificateInfo()
+    elif key_type == 'ed25519-sk':
+        cert_info = OpensshSKED25519CertificateInfo()
     else:
         raise ValueError("%s is not a valid key type" % key_type)
 

plugins/module_utils/openssh/utils.py

@@ -87,6 +87,7 @@ def secure_write(path, mode, content):
 class OpensshParser(object):
     """Parser for OpenSSH encoded objects"""
     BOOLEAN_OFFSET = 1
+    UINT8_OFFSET = 1
     UINT32_OFFSET = 4
     UINT64_OFFSET = 8
 
@@ -104,6 +105,13 @@ class OpensshParser(object):
         self._pos = next_pos
         return value
 
+    def uint8(self):
+        next_pos = self._check_position(self.UINT8_OFFSET)
+
+        value = _UBYTE.unpack(self._data[self._pos:next_pos])[0]
+        self._pos = next_pos
+        return value
+
     def uint32(self):
         next_pos = self._check_position(self.UINT32_OFFSET)
 
@@ -189,7 +197,6 @@ class OpensshParser(object):
         signature_type = parser.string()
         signature_blob = parser.string()
 
-        blob_parser = cls(signature_blob)
         if signature_type in (b'ssh-rsa', b'rsa-sha2-256', b'rsa-sha2-512'):
             # https://datatracker.ietf.org/doc/html/rfc4253#section-6.6
             # https://datatracker.ietf.org/doc/html/rfc8332#section-3
@@ -198,17 +205,22 @@ class OpensshParser(object):
             # https://datatracker.ietf.org/doc/html/rfc4253#section-6.6
             signature_data['r'] = cls._big_int(signature_blob[:20], "big")
             signature_data['s'] = cls._big_int(signature_blob[20:], "big")
-        elif signature_type in (b'ecdsa-sha2-nistp256', b'ecdsa-sha2-nistp384', b'ecdsa-sha2-nistp521'):
+        elif signature_type in (b'ecdsa-sha2-nistp256', b'ecdsa-sha2-nistp384', b'ecdsa-sha2-nistp521', b'sk-ecdsa-sha2-nistp256@openssh.com'):
             # https://datatracker.ietf.org/doc/html/rfc5656#section-3.1.2
+            blob_parser = cls(signature_blob)
             signature_data['r'] = blob_parser.mpint()
             signature_data['s'] = blob_parser.mpint()
-        elif signature_type == b'ssh-ed25519':
+        elif signature_type in (b'ssh-ed25519', b'sk-ssh-ed25519@openssh.com'):
             # https://datatracker.ietf.org/doc/html/rfc8032#section-5.1.2
             signature_data['R'] = cls._big_int(signature_blob[:32], "little")
             signature_data['S'] = cls._big_int(signature_blob[32:], "little")
         else:
             raise ValueError("%s is not a valid signature type" % signature_type)
 
+        if signature_type.startswith(b'sk-'):
+            signature_data['signature_flags'] = parser.uint8()
+            signature_data['signature_counter'] = parser.uint32()
+
         signature_data['signature_type'] = signature_type
 
         return signature_data