Current File : //lib/python3/dist-packages/twisted/conch/ssh/_kex.py
# -*- test-case-name: twisted.conch.test.test_transport -*-
# Copyright (c) Twisted Matrix Laboratories.
# See LICENSE for details.
"""
SSH key exchange handling.
"""
from hashlib import sha1, sha256, sha384, sha512
from zope.interface import Attribute, Interface, implementer
from twisted.conch import error
class _IKexAlgorithm(Interface):
"""
An L{_IKexAlgorithm} describes a key exchange algorithm.
"""
preference = Attribute(
"An L{int} giving the preference of the algorithm when negotiating "
"key exchange. Algorithms with lower precedence values are more "
"preferred."
)
hashProcessor = Attribute(
"A callable hash algorithm constructor (e.g. C{hashlib.sha256}) "
"suitable for use with this key exchange algorithm."
)
class _IFixedGroupKexAlgorithm(_IKexAlgorithm):
"""
An L{_IFixedGroupKexAlgorithm} describes a key exchange algorithm with a
fixed prime / generator group.
"""
prime = Attribute(
"An L{int} giving the prime number used in Diffie-Hellman key "
"exchange, or L{None} if not applicable."
)
generator = Attribute(
"An L{int} giving the generator number used in Diffie-Hellman key "
"exchange, or L{None} if not applicable. (This is not related to "
"Python generator functions.)"
)
class _IEllipticCurveExchangeKexAlgorithm(_IKexAlgorithm):
"""
An L{_IEllipticCurveExchangeKexAlgorithm} describes a key exchange algorithm
that uses an elliptic curve exchange between the client and server.
"""
class _IGroupExchangeKexAlgorithm(_IKexAlgorithm):
"""
An L{_IGroupExchangeKexAlgorithm} describes a key exchange algorithm
that uses group exchange between the client and server.
A prime / generator group should be chosen at run time based on the
requested size. See RFC 4419.
"""
@implementer(_IEllipticCurveExchangeKexAlgorithm)
class _Curve25519SHA256:
"""
Elliptic Curve Key Exchange using Curve25519 and SHA256. Defined in
U{https://datatracker.ietf.org/doc/draft-ietf-curdle-ssh-curves/}.
"""
preference = 1
hashProcessor = sha256
@implementer(_IEllipticCurveExchangeKexAlgorithm)
class _Curve25519SHA256LibSSH:
"""
As L{_Curve25519SHA256}, but with a pre-standardized algorithm name.
"""
preference = 2
hashProcessor = sha256
@implementer(_IEllipticCurveExchangeKexAlgorithm)
class _ECDH256:
"""
Elliptic Curve Key Exchange with SHA-256 as HASH. Defined in
RFC 5656.
Note that C{ecdh-sha2-nistp256} takes priority over nistp384 or nistp512.
This is the same priority from OpenSSH.
C{ecdh-sha2-nistp256} is considered preety good cryptography.
If you need something better consider using C{curve25519-sha256}.
"""
preference = 3
hashProcessor = sha256
@implementer(_IEllipticCurveExchangeKexAlgorithm)
class _ECDH384:
"""
Elliptic Curve Key Exchange with SHA-384 as HASH. Defined in
RFC 5656.
"""
preference = 4
hashProcessor = sha384
@implementer(_IEllipticCurveExchangeKexAlgorithm)
class _ECDH512:
"""
Elliptic Curve Key Exchange with SHA-512 as HASH. Defined in
RFC 5656.
"""
preference = 5
hashProcessor = sha512
@implementer(_IGroupExchangeKexAlgorithm)
class _DHGroupExchangeSHA256:
"""
Diffie-Hellman Group and Key Exchange with SHA-256 as HASH. Defined in
RFC 4419, 4.2.
"""
preference = 6
hashProcessor = sha256
@implementer(_IGroupExchangeKexAlgorithm)
class _DHGroupExchangeSHA1:
"""
Diffie-Hellman Group and Key Exchange with SHA-1 as HASH. Defined in
RFC 4419, 4.1.
"""
preference = 7
hashProcessor = sha1
@implementer(_IFixedGroupKexAlgorithm)
class _DHGroup14SHA1:
"""
Diffie-Hellman key exchange with SHA-1 as HASH and Oakley Group 14
(2048-bit MODP Group). Defined in RFC 4253, 8.2.
"""
preference = 8
hashProcessor = sha1
# Diffie-Hellman primes from Oakley Group 14 (RFC 3526, 3).
prime = int(
"323170060713110073003389139264238282488179412411402391128420"
"097514007417066343542226196894173635693471179017379097041917"
"546058732091950288537589861856221532121754125149017745202702"
"357960782362488842461894775876411059286460994117232454266225"
"221932305409190376805242355191256797158701170010580558776510"
"388618472802579760549035697325615261670813393617995413364765"
"591603683178967290731783845896806396719009772021941686472258"
"710314113364293195361934716365332097170774482279885885653692"
"086452966360772502689555059283627511211740969729980684105543"
"595848665832916421362182310789909994486524682624169720359118"
"52507045361090559"
)
generator = 2
# Which ECDH hash function to use is dependent on the size.
_kexAlgorithms = {
b"curve25519-sha256": _Curve25519SHA256(),
b"curve25519-sha256@libssh.org": _Curve25519SHA256LibSSH(),
b"diffie-hellman-group-exchange-sha256": _DHGroupExchangeSHA256(),
b"diffie-hellman-group-exchange-sha1": _DHGroupExchangeSHA1(),
b"diffie-hellman-group14-sha1": _DHGroup14SHA1(),
b"ecdh-sha2-nistp256": _ECDH256(),
b"ecdh-sha2-nistp384": _ECDH384(),
b"ecdh-sha2-nistp521": _ECDH512(),
}
def getKex(kexAlgorithm):
"""
Get a description of a named key exchange algorithm.
@param kexAlgorithm: The key exchange algorithm name.
@type kexAlgorithm: L{bytes}
@return: A description of the key exchange algorithm named by
C{kexAlgorithm}.
@rtype: L{_IKexAlgorithm}
@raises ConchError: if the key exchange algorithm is not found.
"""
if kexAlgorithm not in _kexAlgorithms:
raise error.ConchError(f"Unsupported key exchange algorithm: {kexAlgorithm}")
return _kexAlgorithms[kexAlgorithm]
def isEllipticCurve(kexAlgorithm):
"""
Returns C{True} if C{kexAlgorithm} is an elliptic curve.
@param kexAlgorithm: The key exchange algorithm name.
@type kexAlgorithm: C{str}
@return: C{True} if C{kexAlgorithm} is an elliptic curve,
otherwise C{False}.
@rtype: C{bool}
"""
return _IEllipticCurveExchangeKexAlgorithm.providedBy(getKex(kexAlgorithm))
def isFixedGroup(kexAlgorithm):
"""
Returns C{True} if C{kexAlgorithm} has a fixed prime / generator group.
@param kexAlgorithm: The key exchange algorithm name.
@type kexAlgorithm: L{bytes}
@return: C{True} if C{kexAlgorithm} has a fixed prime / generator group,
otherwise C{False}.
@rtype: L{bool}
"""
return _IFixedGroupKexAlgorithm.providedBy(getKex(kexAlgorithm))
def getHashProcessor(kexAlgorithm):
"""
Get the hash algorithm callable to use in key exchange.
@param kexAlgorithm: The key exchange algorithm name.
@type kexAlgorithm: L{bytes}
@return: A callable hash algorithm constructor (e.g. C{hashlib.sha256}).
@rtype: C{callable}
"""
kex = getKex(kexAlgorithm)
return kex.hashProcessor
def getDHGeneratorAndPrime(kexAlgorithm):
"""
Get the generator and the prime to use in key exchange.
@param kexAlgorithm: The key exchange algorithm name.
@type kexAlgorithm: L{bytes}
@return: A L{tuple} containing L{int} generator and L{int} prime.
@rtype: L{tuple}
"""
kex = getKex(kexAlgorithm)
return kex.generator, kex.prime
def getSupportedKeyExchanges():
"""
Get a list of supported key exchange algorithm names in order of
preference.
@return: A C{list} of supported key exchange algorithm names.
@rtype: C{list} of L{bytes}
"""
from cryptography.hazmat.backends import default_backend
from cryptography.hazmat.primitives.asymmetric import ec
from twisted.conch.ssh.keys import _curveTable
backend = default_backend()
kexAlgorithms = _kexAlgorithms.copy()
for keyAlgorithm in list(kexAlgorithms):
if keyAlgorithm.startswith(b"ecdh"):
keyAlgorithmDsa = keyAlgorithm.replace(b"ecdh", b"ecdsa")
supported = backend.elliptic_curve_exchange_algorithm_supported(
ec.ECDH(), _curveTable[keyAlgorithmDsa]
)
elif keyAlgorithm.startswith(b"curve25519-sha256"):
supported = backend.x25519_supported()
else:
supported = True
if not supported:
kexAlgorithms.pop(keyAlgorithm)
return sorted(
kexAlgorithms, key=lambda kexAlgorithm: kexAlgorithms[kexAlgorithm].preference
)
Mini Shell