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