102 lines
3.4 KiB
Python
102 lines
3.4 KiB
Python
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import struct
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from cryptography.hazmat.backends import default_backend
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from cryptography.hazmat.primitives import hashes
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from cryptography.hazmat.primitives.asymmetric import dsa, utils
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from dns.dnssecalgs.cryptography import CryptographyPrivateKey, CryptographyPublicKey
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from dns.dnssectypes import Algorithm
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from dns.rdtypes.ANY.DNSKEY import DNSKEY
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class PublicDSA(CryptographyPublicKey):
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key: dsa.DSAPublicKey
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key_cls = dsa.DSAPublicKey
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algorithm = Algorithm.DSA
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chosen_hash = hashes.SHA1()
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def verify(self, signature: bytes, data: bytes) -> None:
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sig_r = signature[1:21]
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sig_s = signature[21:]
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sig = utils.encode_dss_signature(
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int.from_bytes(sig_r, "big"), int.from_bytes(sig_s, "big")
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)
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self.key.verify(sig, data, self.chosen_hash)
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def encode_key_bytes(self) -> bytes:
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"""Encode a public key per RFC 2536, section 2."""
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pn = self.key.public_numbers()
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dsa_t = (self.key.key_size // 8 - 64) // 8
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if dsa_t > 8:
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raise ValueError("unsupported DSA key size")
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octets = 64 + dsa_t * 8
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res = struct.pack("!B", dsa_t)
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res += pn.parameter_numbers.q.to_bytes(20, "big")
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res += pn.parameter_numbers.p.to_bytes(octets, "big")
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res += pn.parameter_numbers.g.to_bytes(octets, "big")
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res += pn.y.to_bytes(octets, "big")
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return res
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@classmethod
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def from_dnskey(cls, key: DNSKEY) -> "PublicDSA":
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cls._ensure_algorithm_key_combination(key)
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keyptr = key.key
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(t,) = struct.unpack("!B", keyptr[0:1])
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keyptr = keyptr[1:]
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octets = 64 + t * 8
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dsa_q = keyptr[0:20]
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keyptr = keyptr[20:]
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dsa_p = keyptr[0:octets]
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keyptr = keyptr[octets:]
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dsa_g = keyptr[0:octets]
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keyptr = keyptr[octets:]
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dsa_y = keyptr[0:octets]
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return cls(
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key=dsa.DSAPublicNumbers( # type: ignore
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int.from_bytes(dsa_y, "big"),
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dsa.DSAParameterNumbers(
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int.from_bytes(dsa_p, "big"),
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int.from_bytes(dsa_q, "big"),
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int.from_bytes(dsa_g, "big"),
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),
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).public_key(default_backend()),
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)
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class PrivateDSA(CryptographyPrivateKey):
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key: dsa.DSAPrivateKey
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key_cls = dsa.DSAPrivateKey
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public_cls = PublicDSA
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def sign(self, data: bytes, verify: bool = False) -> bytes:
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"""Sign using a private key per RFC 2536, section 3."""
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public_dsa_key = self.key.public_key()
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if public_dsa_key.key_size > 1024:
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raise ValueError("DSA key size overflow")
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der_signature = self.key.sign(data, self.public_cls.chosen_hash)
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dsa_r, dsa_s = utils.decode_dss_signature(der_signature)
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dsa_t = (public_dsa_key.key_size // 8 - 64) // 8
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octets = 20
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signature = (
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struct.pack("!B", dsa_t)
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+ int.to_bytes(dsa_r, length=octets, byteorder="big")
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+ int.to_bytes(dsa_s, length=octets, byteorder="big")
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)
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if verify:
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self.public_key().verify(signature, data)
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return signature
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@classmethod
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def generate(cls, key_size: int) -> "PrivateDSA":
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return cls(
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key=dsa.generate_private_key(key_size=key_size),
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)
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class PublicDSANSEC3SHA1(PublicDSA):
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algorithm = Algorithm.DSANSEC3SHA1
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class PrivateDSANSEC3SHA1(PrivateDSA):
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public_cls = PublicDSANSEC3SHA1
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