87 lines
2.8 KiB
Python
87 lines
2.8 KiB
Python
import base64, enum, hashlib, hmac, uuid
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def _scram_nonce():
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return uuid.uuid4().hex.encode("utf8")
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def _scram_escape(s):
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return s.replace(b"=", b"=3D").replace(b",", b"=2C")
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def _scram_unescape(s):
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return s.replace(b"=3D", b"=").replace(b"=2C", b",")
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def _scram_xor(s1, s2):
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return bytes(a ^ b for a, b in zip(s1, s2))
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class SCRAMState(enum.Enum):
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Uninitialised = 0
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ClientFirst = 1
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ClientFinal = 2
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Success = 3
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VerifyFailed = 4
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class SCRAMError(Exception):
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pass
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class SCRAM(object):
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def __init__(self, algo, username, password):
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self._algo = algo
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self._username = username.encode("utf8")
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self._password = password.encode("utf8")
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self.state = SCRAMState.Uninitialised
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self._client_first = None
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self._salted_password = None
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self._auth_message = None
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def _get_data(self, message):
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data = base64.b64decode(message)
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return data, dict(piece.split(b"=", 1) for piece in data.split(b","))
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def client_first(self):
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self.state = SCRAMState.ClientFirst
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# start SCRAM handshake
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self._client_first = b"n=%s,r=%s" % (
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_scram_escape(self._username), _scram_nonce())
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return b"n,,%s" % self._client_first
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def server_first(self, message):
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self.state = SCRAMState.ClientFinal
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data, pieces = self._get_data(message)
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# server-first-message
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nonce = pieces[b"r"]
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salt = base64.b64decode(pieces[b"s"])
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iterations = pieces[b"i"]
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password = self._password
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salted_password = hashlib.pbkdf2_hmac(self._algo, password, salt,
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int(iterations), dklen=None)
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self._salted_password = salted_password
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client_key = hmac.digest(salted_password, b"Client Key", self._algo)
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stored_key = hashlib.new(self._algo, client_key).digest()
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channel = base64.b64encode(b"n,,")
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auth_noproof = b"c=%s,r=%s" % (channel, nonce)
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auth_message = b"%s,%s,%s" % (self._client_first, data, auth_noproof)
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self._auth_message = auth_message
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client_signature = hmac.digest(stored_key, auth_message, self._algo)
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client_proof = base64.b64encode(
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_scram_xor(client_key, client_signature))
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return auth_noproof + (b",p=%s" % client_proof)
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def server_final(self, message):
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# server-final-message
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data, pieces = self._get_data(message)
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verifier = pieces[b"v"]
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server_key = hmac.digest(self._salted_password, b"Server Key",
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self._algo)
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server_signature = hmac.digest(server_key, self._auth_message,
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self._algo)
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if server_signature != base64.b64decode(verifier):
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self.state = SCRAMState.VerifyFailed
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return None
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else:
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self.state = SCRAMState.Success
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return "+"
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