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# Copyright (c) 2013-2024 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 key exchange handlers"""
import binascii
from hashlib import md5
from typing import TYPE_CHECKING, Dict, List, Sequence, Tuple, Type
from .logging import SSHLogger
from .misc import HashType
from .packet import SSHPacketHandler
if TYPE_CHECKING:
# pylint: disable=cyclic-import
from .connection import SSHConnection
_KexAlgList = List[bytes]
_KexAlgMap = Dict[bytes, Tuple[Type['Kex'], HashType, object]]
_kex_algs: _KexAlgList = []
_default_kex_algs:_KexAlgList = []
_kex_handlers: _KexAlgMap = {}
_gss_kex_algs: _KexAlgList = []
_default_gss_kex_algs: _KexAlgList = []
_gss_kex_handlers: _KexAlgMap = {}
class Kex(SSHPacketHandler):
"""Parent class for key exchange handlers"""
def __init__(self, alg: bytes, conn: 'SSHConnection', hash_alg: HashType):
self.algorithm = alg
self._conn = conn
self._logger = conn.logger
self._hash_alg = hash_alg
async def start(self) -> None:
"""Start key exchange"""
raise NotImplementedError
def send_packet(self, pkttype: int, *args: bytes) -> None:
"""Send a kex packet"""
self._conn.send_packet(pkttype, *args, handler=self)
@property
def logger(self) -> SSHLogger:
"""A logger associated with this connection"""
return self._logger
def compute_key(self, k: bytes, h: bytes, x: bytes,
session_id: bytes, keylen: int) -> bytes:
"""Compute keys from output of key exchange"""
key = b''
while len(key) < keylen:
hash_obj = self._hash_alg()
hash_obj.update(k)
hash_obj.update(h)
hash_obj.update(key if key else x + session_id)
key += hash_obj.digest()
return key[:keylen]
def register_kex_alg(alg: bytes, handler: Type[Kex], hash_alg: HashType,
args: Tuple, default: bool) -> None:
"""Register a key exchange algorithm"""
_kex_algs.append(alg)
if default:
_default_kex_algs.append(alg)
_kex_handlers[alg] = (handler, hash_alg, args)
def register_gss_kex_alg(alg: bytes, handler: Type[Kex], hash_alg: HashType,
args: Tuple, default: bool) -> None:
"""Register a GSSAPI key exchange algorithm"""
_gss_kex_algs.append(alg)
if default:
_default_gss_kex_algs.append(alg)
_gss_kex_handlers[alg] = (handler, hash_alg, args)
def get_kex_algs() -> List[bytes]:
"""Return supported key exchange algorithms"""
return _gss_kex_algs + _kex_algs
def get_default_kex_algs() -> List[bytes]:
"""Return default key exchange algorithms"""
return _default_gss_kex_algs + _default_kex_algs
def expand_kex_algs(kex_algs: Sequence[bytes], mechs: Sequence[bytes],
host_key_available: bool) -> List[bytes]:
"""Add mechanisms to GSS entries in key exchange algorithm list"""
expanded_kex_algs: List[bytes] = []
for alg in kex_algs:
if alg.startswith(b'gss-'):
for mech in mechs:
suffix = b'-' + binascii.b2a_base64(md5(mech).digest())[:-1]
expanded_kex_algs.append(alg + suffix)
elif host_key_available:
expanded_kex_algs.append(alg)
return expanded_kex_algs
def get_kex(conn: 'SSHConnection', alg: bytes) -> Kex:
"""Return a key exchange handler
The function looks up a key exchange algorithm and returns a
handler which can perform that type of key exchange.
"""
if alg.startswith(b'gss-'):
alg = alg.rsplit(b'-', 1)[0]
handler, hash_alg, args = _gss_kex_handlers[alg]
else:
handler, hash_alg, args = _kex_handlers[alg]
return handler(alg, conn, hash_alg, *args)
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