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Diffstat (limited to 'src/ssh_audit/kexdh.py')
| -rw-r--r-- | src/ssh_audit/kexdh.py | 409 |
1 files changed, 409 insertions, 0 deletions
diff --git a/src/ssh_audit/kexdh.py b/src/ssh_audit/kexdh.py new file mode 100644 index 0000000..cdefd4e --- /dev/null +++ b/src/ssh_audit/kexdh.py @@ -0,0 +1,409 @@ +""" + The MIT License (MIT) + + 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 + of this software and associated documentation files (the "Software"), to deal + in the Software without restriction, including without limitation the rights + to use, copy, modify, merge, publish, distribute, sublicense, and/or sell + copies of the Software, and to permit persons to whom the Software is + furnished to do so, subject to the following conditions: + + The above copyright notice and this permission notice shall be included in + all copies or substantial portions of the Software. + + THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR + IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, + FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE + AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER + LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, + OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN + THE SOFTWARE. +""" +import binascii +import os +import random +import struct +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 ssh_audit.outputbuffer import OutputBuffer +from ssh_audit.protocol import Protocol +from ssh_audit.ssh_socket import SSH_Socket + + +class KexDHException(Exception): + pass + + +class KexDH: # pragma: nocover + 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 + self.__p = 0 + self.__q = 0 + self.__x = 0 + self.__e = 0 + self.set_params(g, p) + + self.__ed25519_pubkey: Optional[bytes] = None # pylint: disable=unused-private-member + 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: + self.__g = g + self.__p = p + self.__q = (self.__p - 1) // 2 + self.__x = 0 + self.__e = 0 + + def send_init(self, s: SSH_Socket, init_msg: int = Protocol.MSG_KEXDH_INIT) -> None: + r = random.SystemRandom() + self.__x = r.randrange(2, self.__q) + self.__e = pow(self.__g, self.__x, self.__p) + s.write_byte(init_msg) + s.write_mpint2(self.__e) + s.send_packet() + + # Parse a KEXDH_REPLY or KEXDH_GEX_REPLY message from the server. This + # 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. + while packet_type == Protocol.MSG_DEBUG: + packet_type, payload = s.read_packet(2) + + if packet_type != -1 and packet_type not in [Protocol.MSG_KEXDH_REPLY, Protocol.MSG_KEXDH_GEX_REPLY]: # pylint: disable=no-else-raise + raise KexDHException('Expected MSG_KEXDH_REPLY (%d) or MSG_KEXDH_GEX_REPLY (%d), but got %d instead.' % (Protocol.MSG_KEXDH_REPLY, Protocol.MSG_KEXDH_GEX_REPLY, packet_type)) + elif packet_type == -1: + # 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 + + # Get the host key blob, F, and signature. + ptr = 0 + 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: + return hostkey + + _, _, ptr = KexDH.__get_bytes(payload, ptr) + _, _, ptr = KexDH.__get_bytes(payload, ptr) + + # Now pick apart the host key blob. + # Get the host key type (i.e.: 'ssh-rsa', 'ssh-ed25519', etc). + ptr = 0 + 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('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, _, ptr = KexDH.__get_bytes(hostkey, ptr) + self.__hostkey_e = int(binascii.hexlify(hostkey_e), 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 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] + ptr += 4 + return buf[ptr:ptr + num_bytes], num_bytes, ptr + num_bytes + + # Converts a modulus length in bytes to its size in bits, after some + # possible adjustments. + @staticmethod + def __adjust_key_size(size: int) -> int: + size = size * 8 + # Actual keys are observed to be about 8 bits bigger than expected + # (i.e.: 1024-bit keys have a 1032-bit modulus). Check if this is + # the case, and subtract 8 if so. This simply improves readability + # in the UI. + if (size >> 3) % 2 != 0: + 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) + + # Returns the size of the DH modulus, in bits. + def get_dh_modulus_size(self) -> int: + # -2 to account for the '0b' prefix in the string. + return len(bin(self.__p)) - 2 + + +class KexGroup1(KexDH): # pragma: nocover + def __init__(self, out: 'OutputBuffer') -> None: + # rfc2409: second oakley group + p = int('ffffffffffffffffc90fdaa22168c234c4c6628b80dc1cd129024e088a67cc74020bbea63b139b22514a08798e3404ddef9519b3cd3a431b302b0a6df25f14374fe1356d6d51c245e485b576625e7ec6f44c42e9a637ed6b0bff5cb6f406b7edee386bfb5a899fa5ae9f24117c4b1fe649286651ece65381ffffffffffffffff', 16) + super(KexGroup1, self).__init__(out, 'KexGroup1', 'sha1', 2, p) + + +class KexGroup14(KexDH): # pragma: nocover + def __init__(self, out: 'OutputBuffer', hash_alg: str) -> None: + # rfc3526: 2048-bit modp group + p = int('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', 16) + super(KexGroup14, self).__init__(out, 'KexGroup14', hash_alg, 2, p) + + +class KexGroup14_SHA1(KexGroup14): + def __init__(self, out: 'OutputBuffer') -> None: + super(KexGroup14_SHA1, self).__init__(out, 'sha1') + + +class KexGroup14_SHA256(KexGroup14): + def __init__(self, out: 'OutputBuffer') -> None: + super(KexGroup14_SHA256, self).__init__(out, 'sha256') + + +class KexGroup16_SHA512(KexDH): + def __init__(self, out: 'OutputBuffer') -> None: + # rfc3526: 4096-bit modp group + p = int('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', 16) + super(KexGroup16_SHA512, self).__init__(out, 'KexGroup16_SHA512', 'sha512', 2, p) + + +class KexGroup18_SHA512(KexDH): + def __init__(self, out: 'OutputBuffer') -> None: + # rfc3526: 8192-bit modp group + p = int('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', 16) + super(KexGroup18_SHA512, self).__init__(out, 'KexGroup18_SHA512', 'sha512', 2, p) + + +class KexCurve25519_SHA256(KexDH): + 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. + def send_init(self, s: 'SSH_Socket', init_msg: int = Protocol.MSG_KEXDH_INIT) -> None: + self.__ed25519_pubkey = os.urandom(32) + s.write_byte(init_msg) + s.write_string(self.__ed25519_pubkey) + s.send_packet() + + +class KexNISTP256(KexDH): + 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 + # or import an elliptic curve library in order to randomly generate a + # valid elliptic point each time. Hence, we will simply send a static + # value, which is enough for us to extract the server's host key. + def send_init(self, s: 'SSH_Socket', init_msg: int = Protocol.MSG_KEXDH_INIT) -> None: + s.write_byte(init_msg) + s.write_string(b'\x04\x0b\x60\x44\x9f\x8a\x11\x9e\xc7\x81\x0c\xa9\x98\xfc\xb7\x90\xaa\x6b\x26\x8c\x12\x4a\xc0\x09\xbb\xdf\xc4\x2c\x4c\x2c\x99\xb6\xe1\x71\xa0\xd4\xb3\x62\x47\x74\xb3\x39\x0c\xf2\x88\x4a\x84\x6b\x3b\x15\x77\xa5\x77\xd2\xa9\xc9\x94\xf9\xd5\x66\x19\xcd\x02\x34\xd1') + s.send_packet() + + +class KexNISTP384(KexDH): + 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: + s.write_byte(init_msg) + s.write_string(b'\x04\xe2\x9b\x84\xce\xa1\x39\x50\xfe\x1e\xa3\x18\x70\x1c\xe2\x7a\xe4\xb5\x6f\xdf\x93\x9f\xd4\xf4\x08\xcc\x9b\x02\x10\xa4\xca\x77\x9c\x2e\x51\x44\x1d\x50\x7a\x65\x4e\x7e\x2f\x10\x2d\x2d\x4a\x32\xc9\x8e\x18\x75\x90\x6c\x19\x10\xda\xcc\xa8\xe9\xf4\xc4\x3a\x53\x80\x35\xf4\x97\x9c\x04\x16\xf9\x5a\xdc\xcc\x05\x94\x29\xfa\xc4\xd6\x87\x4e\x13\x21\xdb\x3d\x12\xac\xbd\x20\x3b\x60\xff\xe6\x58\x42') + s.send_packet() + + +class KexNISTP521(KexDH): + 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: + s.write_byte(init_msg) + s.write_string(b'\x04\x01\x02\x90\x29\xe9\x8f\xa8\x04\xaf\x1c\x00\xf9\xc6\x29\xc0\x39\x74\x8e\xea\x47\x7e\x7c\xf7\x15\x6e\x43\x3b\x59\x13\x53\x43\xb0\xae\x0b\xe7\xe6\x7c\x55\x73\x52\xa5\x2a\xc1\x42\xde\xfc\xf4\x1f\x8b\x5a\x8d\xfa\xcd\x0a\x65\x77\xa8\xce\x68\xd2\xc6\x26\xb5\x3f\xee\x4b\x01\x7b\xd2\x96\x23\x69\x53\xc7\x01\xe1\x0d\x39\xe9\x87\x49\x3b\xc8\xec\xda\x0c\xf9\xca\xad\x89\x42\x36\x6f\x93\x78\x78\x31\x55\x51\x09\x51\xc0\x96\xd7\xea\x61\xbf\xc2\x44\x08\x80\x43\xed\xc6\xbb\xfb\x94\xbd\xf8\xdf\x2b\xd8\x0b\x2e\x29\x1b\x8c\xc4\x8a\x04\x2d\x3a') + s.send_packet() + + +class KexGroupExchange(KexDH): + 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) + + # The group exchange starts with sending a message to the server with + # the minimum, maximum, and preferred number of bits are for the DH group. + # The server responds with a generator and prime modulus that matches that, + # then the handshake continues on like a normal DH handshake (except the + # SSH message types differ). + def send_init_gex(self, s: 'SSH_Socket', minbits: int = 1024, prefbits: int = 2048, maxbits: int = 8192) -> None: + + # Send the initial group exchange request. Tell the server what range + # of modulus sizes we will accept, along with our preference. + s.write_byte(Protocol.MSG_KEXDH_GEX_REQUEST) + s.write_int(minbits) + s.write_int(prefbits) + s.write_int(maxbits) + s.send_packet() + + packet_type, payload = s.read_packet(2) + if packet_type not in [Protocol.MSG_KEXDH_GEX_GROUP, Protocol.MSG_DEBUG]: + raise KexDHException('Expected MSG_KEXDH_GEX_REPLY (%d), but got %d instead.' % (Protocol.MSG_KEXDH_GEX_REPLY, packet_type)) + + # Skip any & all MSG_DEBUG messages. + while packet_type == Protocol.MSG_DEBUG: + packet_type, payload = s.read_packet(2) + + try: + # Parse the modulus (p) and generator (g) values from the server. + ptr = 0 + p_len = struct.unpack('>I', payload[ptr:ptr + 4])[0] + ptr += 4 + + p = int(binascii.hexlify(payload[ptr:ptr + p_len]), 16) + ptr += p_len + + g_len = struct.unpack('>I', payload[ptr:ptr + 4])[0] + ptr += 4 + + g = int(binascii.hexlify(payload[ptr:ptr + g_len]), 16) + ptr += g_len + except struct.error: + raise KexDHException("Error while parsing modulus and generator during GEX init: %s" % str(traceback.format_exc())) from None + + # Now that we got the generator and modulus, perform the DH exchange + # like usual. + super(KexGroupExchange, self).set_params(g, p) + super(KexGroupExchange, self).send_init(s, Protocol.MSG_KEXDH_GEX_INIT) + + +class KexGroupExchange_SHA1(KexGroupExchange): + def __init__(self, out: 'OutputBuffer') -> None: + super(KexGroupExchange_SHA1, self).__init__(out, 'KexGroupExchange_SHA1', 'sha1') + + +class KexGroupExchange_SHA256(KexGroupExchange): + def __init__(self, out: 'OutputBuffer') -> None: + super(KexGroupExchange_SHA256, self).__init__(out, 'KexGroupExchange_SHA256', 'sha256') |