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# Copyright (c) 2013-2021 by Ron Frederick <ronf@timeheart.net> and others.
#
# This program and the accompanying materials are made available under
# the terms of the Eclipse Public License v2.0 which accompanies this
# distribution and is available at:
#
# http://www.eclipse.org/legal/epl-2.0/
#
# This program may also be made available under the following secondary
# licenses when the conditions for such availability set forth in the
# Eclipse Public License v2.0 are satisfied:
#
# GNU General Public License, Version 2.0, or any later versions of
# that license
#
# SPDX-License-Identifier: EPL-2.0 OR GPL-2.0-or-later
#
# Contributors:
# Ron Frederick - initial implementation, API, and documentation
"""SSH message authentication handlers"""
from hashlib import md5, sha1, sha224, sha256, sha384, sha512
import hmac
from typing import Dict, Callable, List, Tuple
from .packet import UInt32, UInt64
try:
from .crypto import umac64, umac128
_umac_available = True
except ImportError: # pragma: no cover
_umac_available = False
_MACAlgsArgs = Tuple[bytes, int, int, bool, Callable, Tuple, bool]
_MACHandler = Tuple[Callable, int, Tuple]
_MACParams = Tuple[int, int, bool]
_OPENSSH = b'@openssh.com'
_ETM = b'-etm' + _OPENSSH
_mac_algs: List[bytes] = []
_default_mac_algs: List[bytes] = []
_mac_handler: Dict[bytes, _MACHandler] = {}
_mac_params: Dict[bytes, _MACParams] = {}
class MAC:
"""Parent class for SSH message authentication handlers"""
def __init__(self, key: bytes, hash_size: int):
self._key = key
self._hash_size = hash_size
def sign(self, seq: int, packet: bytes) -> bytes:
"""Compute a signature for a message"""
raise NotImplementedError
def verify(self, seq: int, packet: bytes, sig: bytes) -> bool:
"""Verify the signature of a message"""
raise NotImplementedError
class _NullMAC(MAC):
"""Null message authentication handler"""
def sign(self, seq: int, packet: bytes) -> bytes:
"""Compute a signature for a message"""
return b''
def verify(self, seq: int, packet: bytes, sig: bytes) -> bool:
"""Verify the signature of a message"""
return sig == b''
class _HMAC(MAC):
"""HMAC-based message authentication handler"""
def __init__(self, key: bytes, hash_size: int, hash_alg: Callable):
super().__init__(key, hash_size)
self._hash_alg = hash_alg
def sign(self, seq: int, packet: bytes) -> bytes:
"""Compute a signature for a message"""
data = UInt32(seq) + packet
sig = hmac.new(self._key, data, self._hash_alg).digest()
return sig[:self._hash_size]
def verify(self, seq: int, packet: bytes, sig: bytes) -> bool:
"""Verify the signature of a message"""
return hmac.compare_digest(self.sign(seq, packet), sig)
class _UMAC(MAC):
"""UMAC-based message authentication handler"""
def __init__(self, key: bytes, hash_size: int, umac_alg: Callable):
super().__init__(key, hash_size)
self._umac_alg = umac_alg
def sign(self, seq: int, packet: bytes) -> bytes:
"""Compute a signature for a message"""
return self._umac_alg(self._key, packet, UInt64(seq)).digest()
def verify(self, seq: int, packet: bytes, sig: bytes) -> bool:
"""Verify the signature of a message"""
return hmac.compare_digest(self.sign(seq, packet), sig)
def register_mac_alg(mac_alg: bytes, key_size: int, hash_size: int,
etm: bool, handler: Callable, args: Tuple,
default: bool) -> None:
"""Register a MAC algorithm"""
if mac_alg:
_mac_algs.append(mac_alg)
if default:
_default_mac_algs.append(mac_alg)
_mac_handler[mac_alg] = (handler, hash_size, args)
_mac_params[mac_alg] = (key_size, hash_size, etm)
def get_mac_algs() -> List[bytes]:
"""Return supported MAC algorithms"""
return _mac_algs
def get_default_mac_algs() -> List[bytes]:
"""Return default MAC algorithms"""
return _default_mac_algs
def get_mac_params(mac_alg: bytes) -> _MACParams:
"""Get parameters of a MAC algorithm
This function returns the key and hash sizes of a MAC algorithm and
whether or not to compute the MAC before or after encryption.
"""
return _mac_params[mac_alg]
def get_mac(mac_alg: bytes, key: bytes) -> MAC:
"""Return a MAC handler
This function returns a MAC object initialized with the specified
key that can be used for data signing and verification.
"""
handler, hash_size, args = _mac_handler[mac_alg]
return handler(key, hash_size, *args)
_mac_algs_list: Tuple[_MACAlgsArgs, ...] = (
(b'', 0, 0, False, _NullMAC, (), True),
)
if _umac_available: # pragma: no branch
_mac_algs_list += (
(b'umac-64' + _ETM, 16, 8, True, _UMAC, (umac64,), True),
(b'umac-128' + _ETM, 16, 16, True, _UMAC, (umac128,), True))
_mac_algs_list += (
(b'hmac-sha2-256' + _ETM, 32, 32, True, _HMAC, (sha256,), True),
(b'hmac-sha2-512' + _ETM, 64, 64, True, _HMAC, (sha512,), True),
(b'hmac-sha1' + _ETM, 20, 20, True, _HMAC, (sha1,), True),
(b'hmac-md5' + _ETM, 16, 16, True, _HMAC, (md5,), False),
(b'hmac-sha2-256-96' + _ETM, 32, 12, True, _HMAC, (sha256,), False),
(b'hmac-sha2-512-96' + _ETM, 64, 12, True, _HMAC, (sha512,), False),
(b'hmac-sha1-96' + _ETM, 20, 12, True, _HMAC, (sha1,), False),
(b'hmac-md5-96' + _ETM, 16, 12, True, _HMAC, (md5,), False))
if _umac_available: # pragma: no branch
_mac_algs_list += (
(b'umac-64' + _OPENSSH, 16, 8, False, _UMAC, (umac64,), True),
(b'umac-128' + _OPENSSH, 16, 16, False, _UMAC, (umac128,), True))
_mac_algs_list += (
(b'hmac-sha2-256', 32, 32, False, _HMAC, (sha256,), True),
(b'hmac-sha2-512', 64, 64, False, _HMAC, (sha512,), True),
(b'hmac-sha1', 20, 20, False, _HMAC, (sha1,), True),
(b'hmac-sha256-2@ssh.com', 32, 32, False, _HMAC, (sha256,), True),
(b'hmac-sha224@ssh.com', 28, 28, False, _HMAC, (sha224,), True),
(b'hmac-sha256@ssh.com', 16, 32, False, _HMAC, (sha256,), True),
(b'hmac-sha384@ssh.com', 48, 48, False, _HMAC, (sha384,), True),
(b'hmac-sha512@ssh.com', 64, 64, False, _HMAC, (sha512,), True),
(b'hmac-md5', 16, 16, False, _HMAC, (md5,), False),
(b'hmac-sha2-256-96', 32, 12, False, _HMAC, (sha256,), False),
(b'hmac-sha2-512-96', 64, 12, False, _HMAC, (sha512,), False),
(b'hmac-sha1-96', 20, 12, False, _HMAC, (sha1,), False),
(b'hmac-md5-96', 16, 12, False, _HMAC, (md5,), False))
for _alg, _key_size, _hash_size, _etm, \
_mac_alg, _args, _default in _mac_algs_list:
register_mac_alg(_alg, _key_size, _hash_size, _etm,
_mac_alg, _args, _default)
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