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129 lines
4.4 KiB
Python
129 lines
4.4 KiB
Python
"""
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Ephemeral Elliptic Curve Diffie-Hellman (ECDH) key exchange
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RFC 5656, Section 4
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"""
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from hashlib import sha256, sha384, sha512
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from paramiko.message import Message
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from paramiko.py3compat import byte_chr, long
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from paramiko.ssh_exception import SSHException
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from cryptography.hazmat.backends import default_backend
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from cryptography.hazmat.primitives.asymmetric import ec
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from binascii import hexlify
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_MSG_KEXECDH_INIT, _MSG_KEXECDH_REPLY = range(30, 32)
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c_MSG_KEXECDH_INIT, c_MSG_KEXECDH_REPLY = [byte_chr(c) for c in range(30, 32)]
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class KexNistp256:
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name = "ecdh-sha2-nistp256"
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hash_algo = sha256
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curve = ec.SECP256R1()
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def __init__(self, transport):
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self.transport = transport
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# private key, client public and server public keys
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self.P = long(0)
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self.Q_C = None
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self.Q_S = None
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def start_kex(self):
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self._generate_key_pair()
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if self.transport.server_mode:
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self.transport._expect_packet(_MSG_KEXECDH_INIT)
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return
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m = Message()
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m.add_byte(c_MSG_KEXECDH_INIT)
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# SEC1: V2.0 2.3.3 Elliptic-Curve-Point-to-Octet-String Conversion
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m.add_string(self.Q_C.public_numbers().encode_point())
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self.transport._send_message(m)
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self.transport._expect_packet(_MSG_KEXECDH_REPLY)
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def parse_next(self, ptype, m):
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if self.transport.server_mode and (ptype == _MSG_KEXECDH_INIT):
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return self._parse_kexecdh_init(m)
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elif not self.transport.server_mode and (ptype == _MSG_KEXECDH_REPLY):
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return self._parse_kexecdh_reply(m)
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raise SSHException(
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"KexECDH asked to handle packet type {:d}".format(ptype)
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)
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def _generate_key_pair(self):
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self.P = ec.generate_private_key(self.curve, default_backend())
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if self.transport.server_mode:
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self.Q_S = self.P.public_key()
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return
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self.Q_C = self.P.public_key()
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def _parse_kexecdh_init(self, m):
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Q_C_bytes = m.get_string()
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self.Q_C = ec.EllipticCurvePublicNumbers.from_encoded_point(
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self.curve, Q_C_bytes
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)
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K_S = self.transport.get_server_key().asbytes()
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K = self.P.exchange(ec.ECDH(), self.Q_C.public_key(default_backend()))
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K = long(hexlify(K), 16)
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# compute exchange hash
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hm = Message()
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hm.add(
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self.transport.remote_version,
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self.transport.local_version,
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self.transport.remote_kex_init,
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self.transport.local_kex_init,
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)
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hm.add_string(K_S)
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hm.add_string(Q_C_bytes)
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# SEC1: V2.0 2.3.3 Elliptic-Curve-Point-to-Octet-String Conversion
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hm.add_string(self.Q_S.public_numbers().encode_point())
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hm.add_mpint(long(K))
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H = self.hash_algo(hm.asbytes()).digest()
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self.transport._set_K_H(K, H)
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sig = self.transport.get_server_key().sign_ssh_data(H)
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# construct reply
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m = Message()
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m.add_byte(c_MSG_KEXECDH_REPLY)
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m.add_string(K_S)
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m.add_string(self.Q_S.public_numbers().encode_point())
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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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def _parse_kexecdh_reply(self, m):
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K_S = m.get_string()
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Q_S_bytes = m.get_string()
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self.Q_S = ec.EllipticCurvePublicNumbers.from_encoded_point(
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self.curve, Q_S_bytes
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)
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sig = m.get_binary()
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K = self.P.exchange(ec.ECDH(), self.Q_S.public_key(default_backend()))
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K = long(hexlify(K), 16)
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# compute exchange hash and verify signature
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hm = Message()
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hm.add(
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self.transport.local_version,
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self.transport.remote_version,
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self.transport.local_kex_init,
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self.transport.remote_kex_init,
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)
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hm.add_string(K_S)
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# SEC1: V2.0 2.3.3 Elliptic-Curve-Point-to-Octet-String Conversion
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hm.add_string(self.Q_C.public_numbers().encode_point())
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hm.add_string(Q_S_bytes)
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hm.add_mpint(K)
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self.transport._set_K_H(K, self.hash_algo(hm.asbytes()).digest())
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self.transport._verify_key(K_S, sig)
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self.transport._activate_outbound()
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class KexNistp384(KexNistp256):
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name = "ecdh-sha2-nistp384"
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hash_algo = sha384
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curve = ec.SECP384R1()
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class KexNistp521(KexNistp256):
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name = "ecdh-sha2-nistp521"
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hash_algo = sha512
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curve = ec.SECP521R1()
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