-
Notifications
You must be signed in to change notification settings - Fork 0
/
ssh_server.py
3102 lines (2725 loc) · 116 KB
/
ssh_server.py
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
"""
实现一个 ssh server
ssh 涉及的 rfc 列表: https://www.omnisecu.com/tcpip/important-rfc-related-with-ssh.php
The Secure Shell (SSH) Protocol Assigned Numbers: https://datatracker.ietf.org/doc/html/rfc4250
The Secure Shell (SSH) Protocol Architecture: https://datatracker.ietf.org/doc/html/rfc4251
The Secure Shell (SSH) Authentication Protocol: https://datatracker.ietf.org/doc/html/rfc4252
The Secure Shell (SSH) Transport Layer Protocol: https://datatracker.ietf.org/doc/html/rfc4253
The Secure Shell (SSH) Connection Protocol: https://datatracker.ietf.org/doc/html/rfc4254
"""
import abc
import base64
import copy
import dataclasses
import enum
import fcntl
import hashlib
import os
import pathlib
import pwd
import queue
import secrets
import select
import shlex
import signal
import socket
import socketserver
import struct
import subprocess
import tempfile
import termios
import threading
import typing as t
import cryptography.exceptions
from cryptography.hazmat.primitives import hashes, poly1305, serialization
from cryptography.hazmat.primitives.asymmetric import dh, dsa, ec, rsa
from cryptography.hazmat.primitives.asymmetric.padding import PKCS1v15
from cryptography.hazmat.primitives.asymmetric.utils import decode_dss_signature
from cryptography.hazmat.primitives.asymmetric.x25519 import (
X25519PrivateKey,
X25519PublicKey,
)
from cryptography.hazmat.primitives.ciphers import Cipher, algorithms, modes
from cryptography.hazmat.primitives.ciphers.aead import AESGCM
import logutil
import ssh_mac
from error import (
BadRequestError,
DisconnectError,
PacketTooLargeError,
UnexpectedError,
UnsupportedError,
)
from message import (
Message,
SSHDisconnectReasonID,
SSHExtendedDataType,
SSHMessageID,
SSHOpenReasonCode,
)
logger = logutil.get_logger(__name__)
# 当前文件所在文件夹
FILE_DIR = pathlib.Path(__file__).resolve().parent
SSH_DIR = FILE_DIR / "etc/ssh/"
def _expect(cond: bool, msg: str):
if not cond:
raise UnexpectedError(msg)
def _expect_eq(got, expected):
cond = got == expected
msg = f"expected <{expected}>, but got <{got}>"
_expect(cond, msg)
def _setwinsize(fd, rows, cols):
"""设置 pty 窗口大小
code from https://github.com/pexpect/ptyprocess/blob/ce42a786ff6f4baff71382db9076c7398328abaf/ptyprocess/ptyprocess.py#L118
"""
# Some very old platforms have a bug that causes the value for
# termios.TIOCSWINSZ to be truncated. There was a hack here to work
# around this, but it caused problems with newer platforms so has been
# removed. For details see https://github.com/pexpect/pexpect/issues/39
TIOCSWINSZ = getattr(termios, "TIOCSWINSZ", -2146929561)
# Note, assume ws_xpixel and ws_ypixel are zero.
s = struct.pack("HHHH", rows, cols, 0, 0)
fcntl.ioctl(fd, TIOCSWINSZ, s)
def string_from_file(filepath: t.Union[str, pathlib.Path]) -> str:
with open(filepath, "r", encoding="utf-8") as f:
return f.read()
def bytes_from_file(filepath: t.Union[str, pathlib.Path]) -> bytes:
with open(filepath, "rb") as f:
return f.read()
def lines_from_file(filepath: t.Union[str, pathlib.Path]) -> t.List[str]:
with open(filepath, "r", encoding="utf-8") as f:
return list(f)
@dataclasses.dataclass
class AdoptedAlgorithm:
kex: str = ""
server_host_key: str = ""
# cs: client_to_server
# sc: server_to_client
encryption_cs: str = ""
encryption_sc: str = ""
mac_cs: str = ""
mac_sc: str = ""
compression_cs: str = ""
compression_sc: str = ""
language_cs: str = ""
language_sc: str = ""
class SSHSide(enum.Enum):
server = enum.auto()
client = enum.auto()
#################################
# 密钥交换支持
#################################
@dataclasses.dataclass
class KexResult:
side: SSHSide
# 密钥交换对象
kex: t.Optional["KeyExchangeInterface"]
# shared secret, mpint 格式
K: bytes
H: bytes
session_id: bytes
def compute_key(self, key_size: int, tag: bytes) -> bytes:
"""计算密钥。计算方法如下
o Initial IV client to server: HASH(K || H || "A" || session_id)
(Here K is encoded as mpint and "A" as byte and session_id as raw
data. "A" means the single character A, ASCII 65).
o Initial IV server to client: HASH(K || H || "B" || session_id)
o Encryption key client to server: HASH(K || H || "C" || session_id)
o Encryption key server to client: HASH(K || H || "D" || session_id)
o Integrity key client to server: HASH(K || H || "E" || session_id)
o Integrity key server to client: HASH(K || H || "F" || session_id)
如果长度不够，可以按下面的算法计算
K1 = HASH(K || H || X || session_id) (X is e.g., "A")
K2 = HASH(K || H || K1)
K3 = HASH(K || H || K1 || K2)
...
key = K1 || K2 || K3 || ...
ref: https://datatracker.ietf.org/doc/html/rfc4253#section-7.2
Args:
key_size: 生成的 key 大小，-1 表示使用默认大小
tag: 标记符，就是上面提到的 "A" "B" "C" "D" 等等。
Returns: 密钥
"""
hash_func = self.kex.do_hash
key = hash_func(self.K + self.H + tag + self.session_id)
kx = key
while len(key) < key_size:
hk = hash_func(self.K + self.H + kx)
kx += hk
key += hk
return key[:key_size]
class KeyExchangeInterface(abc.ABC):
"""密钥交换接口"""
# noinspection PyUnusedLocal
@abc.abstractmethod
def __init__(self, transport: "SSHServerTransport", session_id: t.Optional[bytes]):
raise NotImplementedError("__init__")
@abc.abstractmethod
def do_server_exchange(self) -> "KexResult":
raise NotImplementedError("start_server")
@abc.abstractmethod
def do_client_exchange(self) -> "KexResult":
raise NotImplementedError("start_client")
@abc.abstractmethod
def do_hash(self, b: bytes) -> bytes:
raise NotImplementedError("do_hash")
class Curve25519Sha256Kex(KeyExchangeInterface):
"""curve25519-sha256 密钥交换算法
curve25519 密钥交换的一些不同的地方
https://datatracker.ietf.org/doc/html/rfc8731#section-3
"""
def __init__(self, transport: "SSHServerTransport", session_id: t.Optional[bytes]):
self.transport = transport
self.kex_result = KexResult(
transport.side,
self,
b"",
b"",
b"",
)
if session_id:
self.kex_result.session_id = session_id
self.kex_result.kex = self
self.private_key = X25519PrivateKey.generate()
self.public_key = self.private_key.public_key()
self._q_c = b""
self._k_s = b""
self._q_s = self.public_key.public_bytes(
encoding=serialization.Encoding.Raw,
format=serialization.PublicFormat.Raw,
)
self._h = b""
self.host_key = self.transport.get_server_host_key()
def do_server_exchange(self) -> "KexResult":
# client send SSH_MSG_KEX_ECDH_INIT
# byte SSH_MSG_KEX_ECDH_INIT
# string Q_C, client's ephemeral public key octet string
init_message = self.transport.read_message(
SSHMessageID.KEX_ECDH_INIT,
)
self._q_c = init_message.get_string()
# server reply SSH_MSG_KEX_ECDH_REPLY
# byte SSH_MSG_KEX_ECDH_REPLY
# string K_S, server's public host key
# string Q_S, server's ephemeral public key octet string .
# string the signature on the exchange hash
self._k_s = self.host_key.get_k_s()
reply_message = Message()
reply_message.add_message_id(SSHMessageID.KEX_ECDH_REPLY)
reply_message.add_string(self._k_s)
reply_message.add_string(self._q_s)
reply_message.add_string(self._get_signature_on_exchange_hash())
self.transport.write_message(reply_message)
return self.kex_result
def do_client_exchange(self) -> "KexResult":
pass
def _get_signature_on_exchange_hash(self):
"""the signature on the exchange hash
The exchange hash H is computed as the hash of the concatenation of
the following.
string V_C, client's identification string (CR and LF excluded)
string V_S, server's identification string (CR and LF excluded)
string I_C, payload of the client's SSH_MSG_KEXINIT
string I_S, payload of the server's SSH_MSG_KEXINIT
string K_S, server's public host key
string Q_C, client's ephemeral public key octet string.
string Q_S, server's ephemeral public key octet string
mpint K, shared secret
"""
# 计算共享密钥
client_key = X25519PublicKey.from_public_bytes(self._q_c)
k = self.private_key.exchange(client_key)
k = Message.bytes_to_mpint(k)
self.kex_result.K = k
# exchange hash
m = Message()
m.add_string(self.transport.client_version_data)
m.add_string(self.transport.server_version_data)
m.add_string(self.transport.client_algorithms_message.as_bytes())
m.add_string(self.transport.server_algorithms_message.as_bytes())
m.add_string(self._k_s)
m.add_string(self._q_c)
m.add_string(self._q_s)
m.add_raw_bytes(k)
# 如果这是第一次密钥交换，那么这个 exchange_hash 也是 session_id(rfc 文档里面提到的 session_identifier)
chosen_hash = hashes.SHA256()
hasher = hashes.Hash(chosen_hash)
hasher.update(m.as_bytes())
exchange_hash = hasher.finalize()
self.kex_result.H = exchange_hash
if not self.kex_result.session_id:
self.kex_result.session_id = exchange_hash
sig = self.host_key.get_sign(exchange_hash)
return sig
def do_hash(self, b: bytes) -> bytes:
return hashlib.sha256(b).digest()
class EcdhSha2Nistp256Kex(KeyExchangeInterface):
"""
椭圆曲线的不同类别名字的对应 https://datatracker.ietf.org/doc/html/rfc4492#appendix-A
不同类别椭圆曲线使用的 hash 算法
https://www.rfc-editor.org/rfc/inline-errata/rfc5656.html
6.2.1. Elliptic Curve Digital Signature Algorithm
+----------------+----------------+
| Curve Size | Hash Algorithm |
+----------------+----------------+
| b <= 256 | SHA-256 |
| | |
| 256 < b <= 384 | SHA-384 |
| | |
| 384 < b | SHA-512 |
+----------------+----------------+
"""
hash_call = hashlib.sha256
curve_cls = ec.SECP256R1
def __init__(self, transport: "SSHServerTransport", session_id: t.Optional[bytes]):
self.transport = transport
self.kex_result = KexResult(
transport.side,
self,
b"",
b"",
b"",
)
if session_id:
self.kex_result.session_id = session_id
self.kex_result.kex = self
self.private_key = ec.generate_private_key(
self.curve_cls(),
)
self.public_key = self.private_key.public_key()
self._q_c = b""
self._k_s = b""
self._q_s = self.public_key.public_bytes(
encoding=serialization.Encoding.X962,
format=serialization.PublicFormat.UncompressedPoint,
)
self._h = b""
self.host_key = None
if transport.side == SSHSide.server:
self.host_key = self.transport.get_server_host_key()
def do_server_exchange(self) -> "KexResult":
# client send SSH_MSG_KEX_ECDH_INIT
# byte SSH_MSG_KEX_ECDH_INIT
# string Q_C, client's ephemeral public key octet string
init_message = self.transport.read_message(
SSHMessageID.KEX_ECDH_INIT,
)
self._q_c = init_message.get_string()
# server reply SSH_MSG_KEX_ECDH_REPLY
# byte SSH_MSG_KEX_ECDH_REPLY
# string K_S, server's public host key
# string Q_S, server's ephemeral public key octet string .
# string the signature on the exchange hash
self._k_s = self.host_key.get_k_s()
reply_message = Message()
reply_message.add_message_id(SSHMessageID.KEX_ECDH_REPLY)
reply_message.add_string(self._k_s)
reply_message.add_string(self._q_s)
reply_message.add_string(self._get_signature_on_exchange_hash())
self.transport.write_message(reply_message)
return self.kex_result
def do_client_exchange(self) -> "KexResult":
pass
def _get_shared_secret(self):
client_key = ec.EllipticCurvePublicKey.from_encoded_point(
self.curve_cls(), self._q_c
)
k = self.private_key.exchange(ec.ECDH(), client_key)
return k
def _get_signature_on_exchange_hash(self):
"""the signature on the exchange hash
The exchange hash H is computed as the hash of the concatenation of
the following.
string V_C, client's identification string (CR and LF excluded)
string V_S, server's identification string (CR and LF excluded)
string I_C, payload of the client's SSH_MSG_KEXINIT
string I_S, payload of the server's SSH_MSG_KEXINIT
string K_S, server's public host key
string Q_C, client's ephemeral public key octet string.
string Q_S, server's ephemeral public key octet string
mpint K, shared secret
"""
# 计算共享密钥
k = self._get_shared_secret()
k = Message.bytes_to_mpint(k)
self.kex_result.K = k
# exchange hash
m = Message()
m.add_string(self.transport.client_version_data)
m.add_string(self.transport.server_version_data)
m.add_string(self.transport.client_algorithms_message.as_bytes())
m.add_string(self.transport.server_algorithms_message.as_bytes())
m.add_string(self._k_s)
m.add_string(self._q_c)
m.add_string(self._q_s)
m.add_raw_bytes(k)
# 如果这是第一次密钥交换，那么这个 exchange_hash 也是 session_id(rfc 文档里面提到的 session_identifier)
exchange_hash = self.do_hash(m.as_bytes())
self.kex_result.H = exchange_hash
if not self.kex_result.session_id:
self.kex_result.session_id = exchange_hash
sig = self.host_key.get_sign(exchange_hash)
return sig
def do_hash(self, b: bytes) -> bytes:
return self.hash_call(b).digest()
class EcdhSha2Nistp384Kex(EcdhSha2Nistp256Kex):
hash_call = hashlib.sha384
curve_cls = ec.SECP384R1
class EcdhSha2Nistp521Kex(EcdhSha2Nistp256Kex):
hash_call = hashlib.sha512
curve_cls = ec.SECP521R1
#################################
# 密钥交换 kex 支持
#################################
def get_dh_prime(
generator: int,
min_bits_of_prime: int,
prefer_bits_of_prime: int,
max_bits_of_prime: int,
) -> int:
"""获取 DH 算法可用的素数。
临时生成太慢了，采用跟 openssh 一样的方式，从预先生成的素数中随机返回一个满足要求的。
如果要自己生成，可参考下面的命令（生成 2048bits 素数）
ssh-keygen -M generate -O bits=2048 moduli-2048.candidates
ssh-keygen -M screen -f moduli-2048.candidates moduli-2048
参考：https://manpages.ubuntu.com/manpages/focal/man1/ssh-keygen.1.html#moduli%20generation
Args:
generator: 算法中的底数 g ，一般是 2 或 5
min_bits_of_prime: 素数 p 的最小比特数
prefer_bits_of_prime: 素数 p 的比特数，优先采用
max_bits_of_prime: 素数 p 的最大比特数
Returns:
可用的素数
"""
MODULI_TESTS_COMPOSITE = 0x1
# openssh 用的这个文件一般是 /etc/ssh/moduli
moduli_filepath = SSH_DIR / "moduli"
lines = lines_from_file(moduli_filepath)
# 满足 prefer_bits_of_prime 条件的素数
prefer_primes = []
# 满足 min_bits_of_prime 和 max_bits_of_prime 条件的素数
match_primes = []
for line in lines:
line = line.strip()
if line.startswith("#"):
# 跳过注释
continue
# 每行是一个素数，一行的元素按空格划分
# 从左到右分别是
# 时间 类型 测试类型 测试次数 比特数 十六进制generator 十六进制素数
# https://man7.org/linux/man-pages/man5/moduli.5.html
parts = line.split()
if parts[1] != "2":
continue
test_flag = int(parts[2])
if test_flag & MODULI_TESTS_COMPOSITE or test_flag == 0:
continue
trials = int(parts[3])
if trials == 0:
continue
# 这个比特数从 0 开始，比如 2048 比特，这个值是 2047
bits = int(parts[4]) + 1
g = int(parts[5], 16)
if g != generator:
continue
p = int(parts[6], 16)
if bits == prefer_bits_of_prime:
prefer_primes.append(p)
elif min_bits_of_prime <= bits <= max_bits_of_prime:
match_primes.append(p)
if prefer_primes:
return secrets.choice(prefer_primes)
if match_primes:
return secrets.choice(match_primes)
raise ValueError("No prime numbers found that meet the requirements.")
class DiffieHellmanGroupExchangeSha256Kex(KeyExchangeInterface):
"""diffie-hellman-group-exchange-sha256
rfc: https://www.rfc-editor.org/rfc/rfc4419
"""
def __init__(self, transport: "SSHServerTransport", session_id: t.Optional[bytes]):
self.transport = transport
self.kex_result = KexResult(
transport.side,
self,
b"",
b"",
b"",
)
if session_id:
self.kex_result.session_id = session_id
self.kex_result.kex = self
self.host_key = self.transport.get_server_host_key()
# 保存计算 exchange hash 需要的信息
self._k_s = self.host_key.get_k_s()
self._min_psize = None
self._prefer_psize = None
self._max_psize = None
self._p = None
self._g = None
self._e = None
self._f = None
self._h = None
self.private_key = None
self.remote_public_key = None
def do_server_exchange(self) -> "KexResult":
# 客户端会先传输自己希望素数 p 有多少个 bit
m = self.transport.read_message(SSHMessageID.KEX_DH_GEX_REQUEST)
min_psize = m.get_uint32()
prefer_psize = m.get_uint32()
max_psize = m.get_uint32()
self._min_psize = min_psize
self._prefer_psize = prefer_psize
self._max_psize = max_psize
logger.debug(
"SSH_MSG_KEX_DH_GEX_REQUEST(%s<%s<%s) received",
min_psize,
prefer_psize,
max_psize,
)
if not (min_psize <= prefer_psize <= max_psize):
raise DisconnectError(
SSHDisconnectReasonID.KEY_EXCHANGE_FAILED,
"invalid size in bits of an acceptable group",
)
# 生成服务端的参数
# https://www.rfc-editor.org/rfc/rfc4419#section-6.1
# generator 推荐使用 2
server_generator = 2
server_prime = get_dh_prime(
server_generator, min_psize, prefer_psize, max_psize
)
server_pn = dh.DHParameterNumbers(server_prime, server_generator)
server_parameters = server_pn.parameters()
self.private_key = server_parameters.generate_private_key()
self._p = server_prime
self._g = server_generator
group_msg = Message()
group_msg.add_message_id(SSHMessageID.KEX_DH_GEX_GROUP)
group_msg.add_mpint(server_prime)
group_msg.add_mpint(server_generator)
self.transport.write_message(group_msg)
logger.debug("SSH_MSG_KEX_DH_GEX_GROUP sent")
m = self.transport.read_message(SSHMessageID.KEX_DH_GEX_INIT)
e = m.get_mpint()
self._e = e
client_pn = dh.DHPublicNumbers(e, server_pn)
self.remote_public_key = client_pn.public_key()
logger.debug("SSH_MSG_KEX_DH_GEX_INIT received")
# 服务器响应
# byte SSH_MSG_KEX_DH_GEX_REPLY
# string server public host key and certificates (K_S)
# mpint f
# string signature of H
reply_message = Message()
reply_message.add_message_id(SSHMessageID.KEX_DH_GEX_REPLY)
reply_message.add_string(self._k_s)
f = self.private_key.public_key().public_numbers().y
self._f = f
reply_message.add_mpint(f)
reply_message.add_string(self._get_signature_on_exchange_hash())
self.transport.write_message(reply_message)
logger.debug("SSH_MSG_KEX_DH_GEX_REPLY sent")
return self.kex_result
def do_client_exchange(self) -> "KexResult":
pass
def _get_shared_secret(self) -> bytes:
k = self.private_key.exchange(self.remote_public_key)
return k
def _get_signature_on_exchange_hash(self):
"""the signature on the exchange hash
The exchange hash H is computed as the hash of the concatenation of
the following.
string V_C, the client's version string (CR and NL excluded)
string V_S, the server's version string (CR and NL excluded)
string I_C, the payload of the client's SSH_MSG_KEXINIT
string I_S, the payload of the server's SSH_MSG_KEXINIT
string K_S, the host key
uint32 min, minimal size in bits of an acceptable group
uint32 n, preferred size in bits of the group the server will send
uint32 max, maximal size in bits of an acceptable group
mpint p, safe prime
mpint g, generator for subgroup
mpint e, exchange value sent by the client
mpint f, exchange value sent by the server
mpint K, the shared secret
"""
# 计算共享密钥
k = self._get_shared_secret()
k = Message.bytes_to_mpint(k)
self.kex_result.K = k
# exchange hash
m = Message()
m.add_string(self.transport.client_version_data)
m.add_string(self.transport.server_version_data)
m.add_string(self.transport.client_algorithms_message.as_bytes())
m.add_string(self.transport.server_algorithms_message.as_bytes())
m.add_string(self._k_s)
m.add_uint32(self._min_psize)
m.add_uint32(self._prefer_psize)
m.add_uint32(self._max_psize)
m.add_mpint(self._p)
m.add_mpint(self._g)
m.add_mpint(self._e)
m.add_mpint(self._f)
m.add_raw_bytes(k)
# 如果这是第一次密钥交换，那么这个 exchange_hash 也是 session_id(rfc 文档里面提到的 session_identifier)
exchange_hash = self.do_hash(m.as_bytes())
self.kex_result.H = exchange_hash
if not self.kex_result.session_id:
self.kex_result.session_id = exchange_hash
sig = self.host_key.get_sign(exchange_hash)
return sig
def do_hash(self, b: bytes) -> bytes:
return hashlib.sha256(b).digest()
class DiffieHellmanGroupExchangeSha1Kex(DiffieHellmanGroupExchangeSha256Kex):
def do_hash(self, b: bytes) -> bytes:
return hashlib.sha1(b).digest()
# diffie-hellman-groupx-shax 算法使用的参数
# 如 diffie-hellman-group16-sha512 使用 group16 的参数
# https://www.rfc-editor.org/rfc/rfc2409#section-6
# https://www.rfc-editor.org/rfc/rfc3526#section-2
oakley_groups = {
"group1": {
"generator": 2,
"prime": int(
"FFFFFFFFFFFFFFFFC90FDAA22168C234C4C6628B80DC1CD129024E088A67CC74020BBEA63B139B22514A08798E3404DDEF9519B3CD3A431B302B0A6DF25F14374FE1356D6D51C245E485B576625E7EC6F44C42E9A63A3620FFFFFFFFFFFFFFFF",
16,
),
},
"group2": {
"generator": 2,
"prime": int(
"FFFFFFFFFFFFFFFFC90FDAA22168C234C4C6628B80DC1CD129024E088A67CC74020BBEA63B139B22514A08798E3404DDEF9519B3CD3A431B302B0A6DF25F14374FE1356D6D51C245E485B576625E7EC6F44C42E9A637ED6B0BFF5CB6F406B7EDEE386BFB5A899FA5AE9F24117C4B1FE649286651ECE65381FFFFFFFFFFFFFFFF",
16,
),
},
"group5": {
"generator": 2,
"prime": int(
"FFFFFFFFFFFFFFFFC90FDAA22168C234C4C6628B80DC1CD129024E088A67CC74020BBEA63B139B22514A08798E3404DDEF9519B3CD3A431B302B0A6DF25F14374FE1356D6D51C245E485B576625E7EC6F44C42E9A637ED6B0BFF5CB6F406B7EDEE386BFB5A899FA5AE9F24117C4B1FE649286651ECE45B3DC2007CB8A163BF0598DA48361C55D39A69163FA8FD24CF5F83655D23DCA3AD961C62F356208552BB9ED529077096966D670C354E4ABC9804F1746C08CA237327FFFFFFFFFFFFFFFF",
16,
),
},
"group14": {
"generator": 2,
"prime": int(
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
16,
),
},
"group15": {
"generator": 2,
"prime": int(
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
16,
),
},
"group16": {
"generator": 2,
"prime": int(
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
16,
),
},
"group17": {
"generator": 2,
"prime": int(
"FFFFFFFFFFFFFFFFC90FDAA22168C234C4C6628B80DC1CD129024E088A67CC74020BBEA63B139B22514A08798E3404DDEF9519B3CD3A431B302B0A6DF25F14374FE1356D6D51C245E485B576625E7EC6F44C42E9A637ED6B0BFF5CB6F406B7EDEE386BFB5A899FA5AE9F24117C4B1FE649286651ECE45B3DC2007CB8A163BF0598DA48361C55D39A69163FA8FD24CF5F83655D23DCA3AD961C62F356208552BB9ED529077096966D670C354E4ABC9804F1746C08CA18217C32905E462E36CE3BE39E772C180E86039B2783A2EC07A28FB5C55DF06F4C52C9DE2BCBF6955817183995497CEA956AE515D2261898FA051015728E5A8AAAC42DAD33170D04507A33A85521ABDF1CBA64ECFB850458DBEF0A8AEA71575D060C7DB3970F85A6E1E4C7ABF5AE8CDB0933D71E8C94E04A25619DCEE3D2261AD2EE6BF12FFA06D98A0864D87602733EC86A64521F2B18177B200CBBE117577A615D6C770988C0BAD946E208E24FA074E5AB3143DB5BFCE0FD108E4B82D120A92108011A723C12A787E6D788719A10BDBA5B2699C327186AF4E23C1A946834B6150BDA2583E9CA2AD44CE8DBBBC2DB04DE8EF92E8EFC141FBECAA6287C59474E6BC05D99B2964FA090C3A2233BA186515BE7ED1F612970CEE2D7AFB81BDD762170481CD0069127D5B05AA993B4EA988D8FDDC186FFB7DC90A6C08F4DF435C93402849236C3FAB4D27C7026C1D4DCB2602646DEC9751E763DBA37BDF8FF9406AD9E530EE5DB382F413001AEB06A53ED9027D831179727B0865A8918DA3EDBEBCF9B14ED44CE6CBACED4BB1BDB7F1447E6CC254B332051512BD7AF426FB8F401378CD2BF5983CA01C64B92ECF032EA15D1721D03F482D7CE6E74FEF6D55E702F46980C82B5A84031900B1C9E59E7C97FBEC7E8F323A97A7E36CC88BE0F1D45B7FF585AC54BD407B22B4154AACC8F6D7EBF48E1D814CC5ED20F8037E0A79715EEF29BE32806A1D58BB7C5DA76F550AA3D8A1FBFF0EB19CCB1A313D55CDA56C9EC2EF29632387FE8D76E3C0468043E8F663F4860EE12BF2D5B0B7474D6E694F91E6DCC4024FFFFFFFFFFFFFFFF",
16,
),
},
"group18": {
"generator": 2,
"prime": int(
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
16,
),
},
}
class DiffieHellmanGroup16Sha512Kex(KeyExchangeInterface):
"""diffie-hellman-group16-sha512
ref: https://www.rfc-editor.org/rfc/rfc4253#section-8
"""
hash_call = hashlib.sha512
group = "group16"
def __init__(self, transport: "SSHServerTransport", session_id: t.Optional[bytes]):
self.transport = transport
self.kex_result = KexResult(
transport.side,
self,
b"",
b"",
b"",
)
if session_id:
self.kex_result.session_id = session_id
self.kex_result.kex = self
self.host_key = self.transport.get_server_host_key()
# 计算 exchange hash 所需信息
self._k_s = self.host_key.get_k_s()
self._e = None
self._f = None
self.private_key = None
self.remote_public_key = None
def do_server_exchange(self) -> "KexResult":
# 生成服务器参数
group = oakley_groups[self.group]
server_pn = dh.DHParameterNumbers(group["prime"], group["generator"])
server_parameters = server_pn.parameters()
self.private_key = server_parameters.generate_private_key()
# First, the client sends the following:
# byte SSH_MSG_KEXDH_INIT
# mpint e
m = self.transport.read_message(SSHMessageID.KEXDH_INIT)
e = m.get_mpint()
self._e = e
client_pn = dh.DHPublicNumbers(e, server_pn)
self.remote_public_key = client_pn.public_key()
logger.debug("SSH_MSG_KEXDH_INIT received")
reply_msg = Message()
reply_msg.add_message_id(SSHMessageID.KEXDH_REPLY)
reply_msg.add_string(self._k_s)
f = self.private_key.public_key().public_numbers().y
self._f = f
reply_msg.add_mpint(f)
reply_msg.add_string(self._get_signature_on_exchange_hash())
self.transport.write_message(reply_msg)
logger.debug("SSH_MSG_KEXDH_REPLY sent")
return self.kex_result
def do_client_exchange(self) -> "KexResult":
pass
def _get_shared_secret(self) -> bytes:
k = self.private_key.exchange(self.remote_public_key)
return k
def _get_signature_on_exchange_hash(self):
"""the signature on the exchange hash
The exchange hash H is computed as the hash of the concatenation of
the following.
string V_C, the client's identification string (CR and LF
excluded)
string V_S, the server's identification string (CR and LF
excluded)
string I_C, the payload of the client's SSH_MSG_KEXINIT
string I_S, the payload of the server's SSH_MSG_KEXINIT
string K_S, the host key
mpint e, exchange value sent by the client
mpint f, exchange value sent by the server
mpint K, the shared secret
"""
# 计算共享密钥
k = self._get_shared_secret()
k = Message.bytes_to_mpint(k)
self.kex_result.K = k
# exchange hash
m = Message()
m.add_string(self.transport.client_version_data)
m.add_string(self.transport.server_version_data)
m.add_string(self.transport.client_algorithms_message.as_bytes())
m.add_string(self.transport.server_algorithms_message.as_bytes())
m.add_string(self._k_s)
m.add_mpint(self._e)
m.add_mpint(self._f)
m.add_raw_bytes(k)
# 如果这是第一次密钥交换，那么这个 exchange_hash 也是 session_id(rfc 文档里面提到的 session_identifier)
exchange_hash = self.do_hash(m.as_bytes())
self.kex_result.H = exchange_hash
if not self.kex_result.session_id:
self.kex_result.session_id = exchange_hash
sig = self.host_key.get_sign(exchange_hash)
return sig
def do_hash(self, b: bytes) -> bytes:
return self.hash_call(b).digest()
class DiffieHellmanGroup18Sha512Kex(DiffieHellmanGroup16Sha512Kex):
hash_call = hashlib.sha512
group = "group18"
class DiffieHellmanGroup14Sha256Kex(DiffieHellmanGroup16Sha512Kex):
hash_call = hashlib.sha256
group = "group14"
class DiffieHellmanGroup14Sha1Kex(DiffieHellmanGroup16Sha512Kex):
hash_call = hashlib.sha1
group = "group14"
class DiffieHellmanGroup1Sha1Kex(DiffieHellmanGroup16Sha512Kex):
hash_call = hashlib.sha1
group = "group1"
def get_kex_obj(algo_name: str) -> t.Type["KeyExchangeInterface"]:
"""根据算法名字获取对应的实现。"""
mapping = {
"curve25519-sha256": Curve25519Sha256Kex,
"[email protected]": Curve25519Sha256Kex,
"ecdh-sha2-nistp256": EcdhSha2Nistp256Kex,
"ecdh-sha2-nistp384": EcdhSha2Nistp384Kex,
"ecdh-sha2-nistp521": EcdhSha2Nistp521Kex,
"diffie-hellman-group-exchange-sha256": DiffieHellmanGroupExchangeSha256Kex,
"diffie-hellman-group-exchange-sha1": DiffieHellmanGroupExchangeSha1Kex,
"diffie-hellman-group16-sha512": DiffieHellmanGroup16Sha512Kex,
"diffie-hellman-group18-sha512": DiffieHellmanGroup18Sha512Kex,
"diffie-hellman-group14-sha256": DiffieHellmanGroup14Sha256Kex,
"diffie-hellman-group14-sha1": DiffieHellmanGroup14Sha1Kex,
"diffie-hellman-group1-sha1": DiffieHellmanGroup1Sha1Kex,
}
return mapping[algo_name]
#################################
# 服务器 host key 支持
#################################
class ServerHostKeyBase(abc.ABC):
"""代表服务器的密钥"""
algo = ""
@abc.abstractmethod
def get_sign(self, data: bytes) -> bytes:
"""对数据进行签名"""
raise NotImplementedError("get_sign")
@abc.abstractmethod
def get_k_s(self) -> bytes:
"""返回用于密钥交换部分的 K_S"""
raise NotImplementedError("get_public_key")
class EcdsaSha2Nistp256HostKey(ServerHostKeyBase):
"""ecdsa-sha2-nistp256 算法
https://datatracker.ietf.org/doc/html/rfc5656
"""
algo = "ecdsa-sha2-nistp256"
category = "nistp256"
def __init__(self, public_key_data: bytes, private_key_data: bytes):
self.public_key = serialization.load_ssh_public_key(public_key_data)
self.private_key = serialization.load_ssh_private_key(private_key_data, None)
def get_k_s(self) -> bytes:
# 下面这些结构格式都是抓包来的，长度都是大端序的 4 个字节
# Host key type length: 19
# Host key type: ecdsa-sha2-nistp256
# ECDSA elliptic curve identifier length: 8
# ECDSA elliptic curve identifier: nistp256
# ECDSA public key length: 65
# ECDSA public key (Q)
# 找到了描述这个结构的文档 https://datatracker.ietf.org/doc/html/rfc5656#section-3.1
raw_key = self.public_key.public_bytes(
encoding=serialization.Encoding.X962,
format=serialization.PublicFormat.UncompressedPoint,
)
m = Message()
m.add_string(self.algo.encode())
m.add_string(self.category.encode())
m.add_string(raw_key)
b = m.as_bytes()
return b
def get_sign(self, data: bytes) -> bytes:
sig = self.private_key.sign(
data,
ec.ECDSA(hashes.SHA256()),
)
# 签名数据结构
# https://datatracker.ietf.org/doc/html/rfc5656#section-3.1.2
r, s = decode_dss_signature(sig)
rs_m = Message()
rs_m.add_mpint(r)
rs_m.add_mpint(s)
# wireshark 抓包拿到的数据结构
# Host signature length
# Host signature type length: 19
# Host signature type: ecdsa-sha2-nistp256
# 签名数据
sig_m = Message()
sig_m.add_string(self.algo.encode())
sig_m.add_string(rs_m.as_bytes())
sig_b = sig_m.as_bytes()
return sig_b
class SSHEd25519HostKey(ServerHostKeyBase):
"""ssh-ed25519 算法
https://www.rfc-editor.org/rfc/rfc8709
"""
algo = "ssh-ed25519"
def __init__(self, public_key_data: bytes, private_key_data: bytes):
self.public_key = serialization.load_ssh_public_key(public_key_data)
self.private_key = serialization.load_ssh_private_key(private_key_data, None)
def get_k_s(self) -> bytes:
# https://www.rfc-editor.org/rfc/rfc8709#section-4
# 结构如下
# string "ssh-ed25519"
# string key
raw_key = self.public_key.public_bytes(
encoding=serialization.Encoding.Raw,
format=serialization.PublicFormat.Raw,
)
m = Message()
m.add_string(self.algo.encode())
m.add_string(raw_key)
b = m.as_bytes()