154 lines
4.3 KiB
Python
154 lines
4.3 KiB
Python
# This file is dual licensed under the terms of the Apache License, Version
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# 2.0, and the BSD License. See the LICENSE file in the root of this repository
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# for complete details.
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from __future__ import absolute_import, division, print_function
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import base64
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import struct
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import six
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from cryptography import utils
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from cryptography.exceptions import UnsupportedAlgorithm
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from cryptography.hazmat.primitives.asymmetric import dsa, ec, ed25519, rsa
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def load_ssh_public_key(data, backend):
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key_parts = data.split(b' ', 2)
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if len(key_parts) < 2:
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raise ValueError(
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'Key is not in the proper format or contains extra data.')
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key_type = key_parts[0]
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if key_type == b'ssh-rsa':
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loader = _load_ssh_rsa_public_key
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elif key_type == b'ssh-dss':
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loader = _load_ssh_dss_public_key
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elif key_type in [
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b'ecdsa-sha2-nistp256', b'ecdsa-sha2-nistp384', b'ecdsa-sha2-nistp521',
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]:
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loader = _load_ssh_ecdsa_public_key
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elif key_type == b'ssh-ed25519':
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loader = _load_ssh_ed25519_public_key
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else:
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raise UnsupportedAlgorithm('Key type is not supported.')
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key_body = key_parts[1]
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try:
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decoded_data = base64.b64decode(key_body)
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except TypeError:
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raise ValueError('Key is not in the proper format.')
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inner_key_type, rest = _ssh_read_next_string(decoded_data)
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if inner_key_type != key_type:
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raise ValueError(
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'Key header and key body contain different key type values.'
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)
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return loader(key_type, rest, backend)
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def _load_ssh_rsa_public_key(key_type, decoded_data, backend):
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e, rest = _ssh_read_next_mpint(decoded_data)
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n, rest = _ssh_read_next_mpint(rest)
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if rest:
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raise ValueError('Key body contains extra bytes.')
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return rsa.RSAPublicNumbers(e, n).public_key(backend)
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def _load_ssh_dss_public_key(key_type, decoded_data, backend):
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p, rest = _ssh_read_next_mpint(decoded_data)
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q, rest = _ssh_read_next_mpint(rest)
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g, rest = _ssh_read_next_mpint(rest)
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y, rest = _ssh_read_next_mpint(rest)
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if rest:
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raise ValueError('Key body contains extra bytes.')
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parameter_numbers = dsa.DSAParameterNumbers(p, q, g)
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public_numbers = dsa.DSAPublicNumbers(y, parameter_numbers)
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return public_numbers.public_key(backend)
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def _load_ssh_ecdsa_public_key(expected_key_type, decoded_data, backend):
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curve_name, rest = _ssh_read_next_string(decoded_data)
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data, rest = _ssh_read_next_string(rest)
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if expected_key_type != b"ecdsa-sha2-" + curve_name:
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raise ValueError(
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'Key header and key body contain different key type values.'
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)
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if rest:
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raise ValueError('Key body contains extra bytes.')
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curve = {
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b"nistp256": ec.SECP256R1,
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b"nistp384": ec.SECP384R1,
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b"nistp521": ec.SECP521R1,
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}[curve_name]()
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if six.indexbytes(data, 0) != 4:
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raise NotImplementedError(
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"Compressed elliptic curve points are not supported"
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)
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return ec.EllipticCurvePublicKey.from_encoded_point(curve, data)
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def _load_ssh_ed25519_public_key(expected_key_type, decoded_data, backend):
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data, rest = _ssh_read_next_string(decoded_data)
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if rest:
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raise ValueError('Key body contains extra bytes.')
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return ed25519.Ed25519PublicKey.from_public_bytes(data)
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def _ssh_read_next_string(data):
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"""
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Retrieves the next RFC 4251 string value from the data.
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While the RFC calls these strings, in Python they are bytes objects.
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"""
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if len(data) < 4:
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raise ValueError("Key is not in the proper format")
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str_len, = struct.unpack('>I', data[:4])
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if len(data) < str_len + 4:
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raise ValueError("Key is not in the proper format")
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return data[4:4 + str_len], data[4 + str_len:]
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def _ssh_read_next_mpint(data):
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"""
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Reads the next mpint from the data.
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Currently, all mpints are interpreted as unsigned.
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"""
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mpint_data, rest = _ssh_read_next_string(data)
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return (
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utils.int_from_bytes(mpint_data, byteorder='big', signed=False), rest
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)
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def _ssh_write_string(data):
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return struct.pack(">I", len(data)) + data
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def _ssh_write_mpint(value):
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data = utils.int_to_bytes(value)
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if six.indexbytes(data, 0) & 0x80:
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data = b"\x00" + data
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return _ssh_write_string(data)
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