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Fix #826: Suppress cryptography FFDH deprecation warning and add decrepit fallback #830

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Fix #826: Suppress cryptography FFDH deprecation warning and add decrepit fallback #830

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29 changes: 22 additions & 7 deletions asyncssh/crypto/dh.py
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Original file line number Diff line number Diff line change
Expand Up @@ -20,27 +20,42 @@

"""A shim around PyCA for Diffie Hellman key exchange"""

from cryptography.hazmat.primitives.asymmetric import dh
import warnings
from cryptography.utils import CryptographyDeprecationWarning

try:
from cryptography.hazmat.primitives.asymmetric import dh
except ImportError:
from cryptography.hazmat.decrepit.asymmetric import dh


class DH:
"""A shim around PyCA for Diffie Hellman key exchange"""

def __init__(self, g: int, p: int):
self._pn = dh.DHParameterNumbers(p, g)
self._priv_key = self._pn.parameters().generate_private_key()
with warnings.catch_warnings():
warnings.simplefilter('ignore', CryptographyDeprecationWarning)

self._pn = dh.DHParameterNumbers(p, g)
self._priv_key = self._pn.parameters().generate_private_key()

def get_public(self) -> int:
"""Return the public key to send in the handshake"""

pub_key = self._priv_key.public_key()
with warnings.catch_warnings():
warnings.simplefilter('ignore', CryptographyDeprecationWarning)

pub_key = self._priv_key.public_key()

return pub_key.public_numbers().y
return pub_key.public_numbers().y

def get_shared(self, peer_public: int) -> int:
"""Return the shared key from the peer's public key"""

peer_key = dh.DHPublicNumbers(peer_public, self._pn).public_key()
shared_key = self._priv_key.exchange(peer_key)
with warnings.catch_warnings():
warnings.simplefilter('ignore', CryptographyDeprecationWarning)

peer_key = dh.DHPublicNumbers(peer_public, self._pn).public_key()
shared_key = self._priv_key.exchange(peer_key)

return int.from_bytes(shared_key, 'big')