RAHHH

backend/lib/python3.12/site-packages/twisted/conch/ssh/_kex.py

@@ -0,0 +1,293 @@
+# -*- 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
+    )