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# Copyright (c) 2013-2023 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
"""Symmetric key encryption handlers"""
from typing import Dict, List, Optional, Tuple, Type
from .crypto import BasicCipher, GCMCipher, ChachaCipher, get_cipher_params
from .mac import MAC, get_mac_params, get_mac
from .packet import UInt64
_EncParams = Tuple[int, int, int, int, int, bool]
_EncParamsMap = Dict[bytes, Tuple[Type['Encryption'], str]]
_enc_algs: List[bytes] = []
_default_enc_algs: List[bytes] = []
_enc_params: _EncParamsMap = {}
class Encryption:
"""Parent class for SSH packet encryption objects"""
@classmethod
def new(cls, cipher_name: str, key: bytes, iv: bytes, mac_alg: bytes = b'',
mac_key: bytes = b'', etm: bool = False) -> 'Encryption':
"""Construct a new SSH packet encryption object"""
raise NotImplementedError
@classmethod
def get_mac_params(cls, mac_alg: bytes) -> Tuple[int, int, bool]:
"""Get parameters of the MAC algorithm used with this encryption"""
return get_mac_params(mac_alg)
def encrypt_packet(self, seq: int, header: bytes,
packet: bytes) -> Tuple[bytes, bytes]:
"""Encrypt and sign an SSH packet"""
raise NotImplementedError
def decrypt_header(self, seq: int, first_block: bytes,
header_len: int) -> Tuple[bytes, bytes]:
"""Decrypt an SSH packet header"""
raise NotImplementedError
def decrypt_packet(self, seq: int, first: bytes, rest: bytes,
header_len: int, mac: bytes) -> Optional[bytes]:
"""Verify the signature of and decrypt an SSH packet"""
raise NotImplementedError
class BasicEncryption(Encryption):
"""Shim for basic encryption"""
def __init__(self, cipher: BasicCipher, mac: MAC):
self._cipher = cipher
self._mac = mac
@classmethod
def new(cls, cipher_name: str, key: bytes, iv: bytes, mac_alg: bytes = b'',
mac_key: bytes = b'', etm: bool = False) -> 'BasicEncryption':
"""Construct a new SSH packet encryption object for basic ciphers"""
cipher = BasicCipher(cipher_name, key, iv)
mac = get_mac(mac_alg, mac_key)
if etm:
return ETMEncryption(cipher, mac)
else:
return cls(cipher, mac)
def encrypt_packet(self, seq: int, header: bytes,
packet: bytes) -> Tuple[bytes, bytes]:
"""Encrypt and sign an SSH packet"""
packet = header + packet
mac = self._mac.sign(seq, packet) if self._mac else b''
return self._cipher.encrypt(packet), mac
def decrypt_header(self, seq: int, first_block: bytes,
header_len: int) -> Tuple[bytes, bytes]:
"""Decrypt an SSH packet header"""
first_block = self._cipher.decrypt(first_block)
return first_block, first_block[:header_len]
def decrypt_packet(self, seq: int, first: bytes, rest: bytes,
header_len: int, mac: bytes) -> Optional[bytes]:
"""Verify the signature of and decrypt an SSH packet"""
packet = first + self._cipher.decrypt(rest)
if self._mac.verify(seq, packet, mac):
return packet[header_len:]
else:
return None
class ETMEncryption(BasicEncryption):
"""Shim for encrypt-then-mac encryption"""
def encrypt_packet(self, seq: int, header: bytes,
packet: bytes) -> Tuple[bytes, bytes]:
"""Encrypt and sign an SSH packet"""
packet = header + self._cipher.encrypt(packet)
return packet, self._mac.sign(seq, packet)
def decrypt_header(self, seq: int, first_block: bytes,
header_len: int) -> Tuple[bytes, bytes]:
"""Decrypt an SSH packet header"""
return first_block, first_block[:header_len]
def decrypt_packet(self, seq: int, first: bytes, rest: bytes,
header_len: int, mac: bytes) -> Optional[bytes]:
"""Verify the signature of and decrypt an SSH packet"""
packet = first + rest
if self._mac.verify(seq, packet, mac):
return self._cipher.decrypt(packet[header_len:])
else:
return None
class GCMEncryption(Encryption):
"""Shim for GCM encryption"""
def __init__(self, cipher: GCMCipher):
self._cipher = cipher
@classmethod
def new(cls, cipher_name: str, key: bytes, iv: bytes, mac_alg: bytes = b'',
mac_key: bytes = b'', etm: bool = False) -> 'GCMEncryption':
"""Construct a new SSH packet encryption object for GCM ciphers"""
return cls(GCMCipher(cipher_name, key, iv))
@classmethod
def get_mac_params(cls, mac_alg: bytes) -> Tuple[int, int, bool]:
"""Get parameters of the MAC algorithm used with this encryption"""
return 0, 16, True
def encrypt_packet(self, seq: int, header: bytes,
packet: bytes) -> Tuple[bytes, bytes]:
"""Encrypt and sign an SSH packet"""
return self._cipher.encrypt_and_sign(header, packet)
def decrypt_header(self, seq: int, first_block: bytes,
header_len: int) -> Tuple[bytes, bytes]:
"""Decrypt an SSH packet header"""
return first_block, first_block[:header_len]
def decrypt_packet(self, seq: int, first: bytes, rest: bytes,
header_len: int, mac: bytes) -> Optional[bytes]:
"""Verify the signature of and decrypt an SSH packet"""
return self._cipher.verify_and_decrypt(first[:header_len],
first[header_len:] + rest, mac)
class ChachaEncryption(Encryption):
"""Shim for chacha20-poly1305 encryption"""
def __init__(self, cipher: ChachaCipher):
self._cipher = cipher
@classmethod
def new(cls, cipher_name: str, key: bytes, iv: bytes, mac_alg: bytes = b'',
mac_key: bytes = b'', etm: bool = False) -> 'ChachaEncryption':
"""Construct a new SSH packet encryption object for Chacha ciphers"""
return cls(ChachaCipher(key))
@classmethod
def get_mac_params(cls, mac_alg: bytes) -> Tuple[int, int, bool]:
"""Get parameters of the MAC algorithm used with this encryption"""
return 0, 16, True
def encrypt_packet(self, seq: int, header: bytes,
packet: bytes) -> Tuple[bytes, bytes]:
"""Encrypt and sign an SSH packet"""
return self._cipher.encrypt_and_sign(header, packet, UInt64(seq))
def decrypt_header(self, seq: int, first_block: bytes,
header_len: int) -> Tuple[bytes, bytes]:
"""Decrypt an SSH packet header"""
return (first_block,
self._cipher.decrypt_header(first_block[:header_len],
UInt64(seq)))
def decrypt_packet(self, seq: int, first: bytes, rest: bytes,
header_len: int, mac: bytes) -> Optional[bytes]:
"""Verify the signature of and decrypt an SSH packet"""
return self._cipher.verify_and_decrypt(first[:header_len],
first[header_len:] + rest,
UInt64(seq), mac)
def register_encryption_alg(enc_alg: bytes, encryption: Type[Encryption],
cipher_name: str, default: bool) -> None:
"""Register an encryption algorithm"""
try:
get_cipher_params(cipher_name)
except KeyError:
pass
else:
_enc_algs.append(enc_alg)
if default:
_default_enc_algs.append(enc_alg)
_enc_params[enc_alg] = (encryption, cipher_name)
def get_encryption_algs() -> List[bytes]:
"""Return supported encryption algorithms"""
return _enc_algs
def get_default_encryption_algs() -> List[bytes]:
"""Return default encryption algorithms"""
return _default_enc_algs
def get_encryption_params(enc_alg: bytes,
mac_alg: bytes = b'') -> _EncParams:
"""Get parameters of an encryption and MAC algorithm"""
encryption, cipher_name = _enc_params[enc_alg]
enc_keysize, enc_ivsize, enc_blocksize = get_cipher_params(cipher_name)
mac_keysize, mac_hashsize, etm = encryption.get_mac_params(mac_alg)
return (enc_keysize, enc_ivsize, enc_blocksize,
mac_keysize, mac_hashsize, etm)
def get_encryption(enc_alg: bytes, key: bytes, iv: bytes, mac_alg: bytes = b'',
mac_key: bytes = b'', etm: bool = False) -> Encryption:
"""Return an object which can encrypt and decrypt SSH packets"""
encryption, cipher_name = _enc_params[enc_alg]
return encryption.new(cipher_name, key, iv, mac_alg, mac_key, etm)
_enc_alg_list = (
(b'chacha20-poly1305@openssh.com', ChachaEncryption,
'chacha20-poly1305', True),
(b'aes256-gcm@openssh.com', GCMEncryption,
'aes256-gcm', True),
(b'aes128-gcm@openssh.com', GCMEncryption,
'aes128-gcm', True),
(b'aes256-ctr', BasicEncryption,
'aes256-ctr', True),
(b'aes192-ctr', BasicEncryption,
'aes192-ctr', True),
(b'aes128-ctr', BasicEncryption,
'aes128-ctr', True),
(b'aes256-cbc', BasicEncryption,
'aes256-cbc', False),
(b'aes192-cbc', BasicEncryption,
'aes192-cbc', False),
(b'aes128-cbc', BasicEncryption,
'aes128-cbc', False),
(b'3des-cbc', BasicEncryption,
'des3-cbc', False),
(b'blowfish-cbc', BasicEncryption,
'blowfish-cbc', False),
(b'cast128-cbc', BasicEncryption,
'cast128-cbc', False),
(b'seed-cbc@ssh.com', BasicEncryption,
'seed-cbc', False),
(b'arcfour256', BasicEncryption,
'arcfour256', False),
(b'arcfour128', BasicEncryption,
'arcfour128', False),
(b'arcfour', BasicEncryption,
'arcfour', False)
)
for _enc_alg_args in _enc_alg_list:
register_encryption_alg(*_enc_alg_args)
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