105 lines
4.3 KiB
Python
105 lines
4.3 KiB
Python
#!/usr/bin/python
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# standard SSH key exchange ("kex" if you wanna sound cool):
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# diffie-hellman of 1024 bit key halves, using a known "p" prime and
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# "g" generator.
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from message import Message, inflate_long
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from secsh import SSHException
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from transport import MSG_NEWKEYS
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from Crypto.Hash import SHA
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from logging import DEBUG, INFO, WARNING, ERROR, CRITICAL
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MSG_KEXDH_INIT, MSG_KEXDH_REPLY = range(30, 32)
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# draft-ietf-secsh-transport-09.txt, page 17
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P = 0xFFFFFFFFFFFFFFFFC90FDAA22168C234C4C6628B80DC1CD129024E088A67CC74020BBEA63B139B22514A08798E3404DDEF9519B3CD3A431B302B0A6DF25F14374FE1356D6D51C245E485B576625E7EC6F44C42E9A637ED6B0BFF5CB6F406B7EDEE386BFB5A899FA5AE9F24117C4B1FE649286651ECE65381FFFFFFFFFFFFFFFFL
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G = 2
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class KexGroup1(object):
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name = 'diffie-hellman-group1-sha1'
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def __init__(self, transport):
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self.transport = transport
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def generate_x(self):
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# generate an "x" (1 < x < q), where q is (p-1)/2.
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# p is a 128-byte (1024-bit) number, where the first 64 bits are 1.
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# therefore q can be approximated as a 2^1023. we drop the subset of
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# potential x where the first 63 bits are 1, because some of those will be
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# larger than q (but this is a tiny tiny subset of potential x).
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while 1:
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self.transport.randpool.stir()
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x_bytes = self.transport.randpool.get_bytes(128)
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x_bytes = chr(ord(x_bytes[0]) & 0x7f) + x_bytes[1:]
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if (x_bytes[:8] != '\x7F\xFF\xFF\xFF\xFF\xFF\xFF\xFF') and \
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(x_bytes[:8] != '\x00\x00\x00\x00\x00\x00\x00\x00'):
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break
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self.x = inflate_long(x_bytes)
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def start_kex(self):
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self.generate_x()
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if self.transport.server_mode:
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# compute f = g^x mod p, but don't send it yet
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self.f = pow(G, self.x, P)
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self.transport.expected_packet = MSG_KEXDH_INIT
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return
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# compute e = g^x mod p (where g=2), and send it
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self.e = pow(G, self.x, P)
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m = Message()
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m.add_byte(chr(MSG_KEXDH_INIT))
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m.add_mpint(self.e)
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self.transport.send_message(m)
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self.transport.expected_packet = MSG_KEXDH_REPLY
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def parse_next(self, ptype, m):
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if self.transport.server_mode and (ptype == MSG_KEXDH_INIT):
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return self.parse_kexdh_init(m)
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elif not self.transport.server_mode and (ptype == MSG_KEXDH_REPLY):
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return self.parse_kexdh_reply(m)
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raise SSHException('KexGroup1 asked to handle packet type %d' % ptype)
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def parse_kexdh_reply(self, m):
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# client mode
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host_key = m.get_string()
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self.f = m.get_mpint()
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if (self.f < 1) or (self.f > P - 1):
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raise SSHException('Server kex "f" is out of range')
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sig = m.get_string()
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K = pow(self.f, self.x, P)
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# okay, build up the hash H of (V_C || V_S || I_C || I_S || K_S || e || f || K)
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hm = Message().add(self.transport.local_version).add(self.transport.remote_version)
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hm.add(self.transport.local_kex_init).add(self.transport.remote_kex_init).add(host_key)
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hm.add(self.e).add(self.f).add(K)
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self.transport.set_K_H(K, SHA.new(str(hm)).digest())
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self.transport.verify_key(host_key, sig)
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self.transport.activate_outbound()
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self.transport.expected_packet = MSG_NEWKEYS
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def parse_kexdh_init(self, m):
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# server mode
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self.e = m.get_mpint()
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if (self.e < 1) or (self.e > P - 1):
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raise SSHException('Client kex "e" is out of range')
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K = pow(self.e, self.x, P)
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key = str(self.transport.get_server_key())
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# okay, build up the hash H of (V_C || V_S || I_C || I_S || K_S || e || f || K)
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hm = Message().add(self.transport.remote_version).add(self.transport.local_version)
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hm.add(self.transport.remote_kex_init).add(self.transport.local_kex_init).add(key)
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hm.add(self.e).add(self.f).add(K)
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H = SHA.new(str(hm)).digest()
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self.transport.set_K_H(K, H)
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# sign it
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sig = self.transport.get_server_key().sign_ssh_data(H)
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# send reply
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m = Message()
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m.add_byte(chr(MSG_KEXDH_REPLY))
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m.add_string(key)
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m.add_mpint(self.f)
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m.add_string(sig)
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self.transport.send_message(m)
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self.transport.activate_outbound()
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self.transport.expected_packet = MSG_NEWKEYS
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