Merge branch 'x25519_curve25519'

Changelog.rst

@@ -8,6 +8,7 @@ Under development
 * Remove support for Python 3.5
 * GH#814: RSA keys for PSS can be imported.
 * GH#810: fixed negation of Ed25519 points
+* Add support for Curve25519 / X25519
 
 3.20.0 (9 January 2024)
 ++++++++++++++++++++++++++

Doc/src/public_key/ecc.rst

@@ -53,18 +53,22 @@ You can also export the public key, which is not sensitive::
    "NIST P-521", "``'NIST P-521'``, ``'p521'``, ``'P-521'``, ``'prime521v1'``, ``'secp521r1'``"
    "Ed25519",    "``'ed25519'``, ``'Ed25519'``"
    "Ed448",      "``'ed448'``, ``'Ed448'``"
+   "Curve25519", "``'curve25519'``, ``'Curve25519'``"
 
 For more information about each NIST curve see `FIPS 186-4`_, Section D.1.2.
 
 The Ed25519 and the Ed448 curves are defined in RFC8032_.
 
-The ECC key can be used to perform or verify signatures, using the modules
+The Curve25519 curve is defined in RFC7748_.
+
+The ECC keys can be used to perform or verify signatures, using the modules
 :mod:`Crypto.Signature.DSS` (ECDSA; NIST curves only)
 or :mod:`Crypto.Signature.eddsa` (EdDSA; Ed25519 and Ed448 curve only).
 
 .. _ECC: http://andrea.corbellini.name/2015/05/17/elliptic-curve-cryptography-a-gentle-introduction/
 .. _`FIPS 186-4`: http://nvlpubs.nist.gov/nistpubs/FIPS/NIST.FIPS.186-4.pdf
 .. _RFC8032: https://datatracker.ietf.org/doc/html/rfc8032
+.. _RFC7748: https://datatracker.ietf.org/doc/html/rfc7748
 
 .. automodule:: Crypto.PublicKey.ECC
     :members:

README.rst

@@ -47,7 +47,7 @@ with respect to the last official version of PyCrypto (2.6.1):
 * Authenticated encryption modes (GCM, CCM, EAX, SIV, OCB)
 * Accelerated AES on Intel platforms via AES-NI
 * First class support for PyPy
-* Elliptic curves cryptography (NIST P-curves; Ed25519, Ed448)
+* Elliptic curves cryptography (NIST P-curves; Ed25519, Ed448, Curve25519)
 * Better and more compact API (`nonce` and `iv` attributes for ciphers,
   automatic generation of random nonces and IVs, simplified CTR cipher mode,
   and more)

lib/Crypto/Protocol/DH.py

@@ -1,16 +1,63 @@
 from Crypto.Util.number import long_to_bytes
-from Crypto.PublicKey.ECC import EccKey
+from Crypto.PublicKey.ECC import (EccKey,
+                                  construct,
+                                  _import_curve25519_public_key)
 
 
 def _compute_ecdh(key_priv, key_pub):
-    # See Section 5.7.1.2 in NIST SP 800-56Ar3
     pointP = key_pub.pointQ * key_priv.d
     if pointP.is_point_at_infinity():
-        raise ValueError("Invalid ECDH point")
-    z = long_to_bytes(pointP.x, pointP.size_in_bytes())
+         raise ValueError("Invalid ECDH point")
+
+    if key_priv.curve == "Curve25519":
+        z = bytearray(pointP.x.to_bytes(32, byteorder='little'))
+    else:
+        # See Section 5.7.1.2 in NIST SP 800-56Ar3
+        z = long_to_bytes(pointP.x, pointP.size_in_bytes())
     return z
 
 
+def import_x25519_public_key(encoded):
+    """Create a new X25519 public key object,
+    starting from the key encoded as raw ``bytes``,
+    in the format described in RFC7748.
+
+    Args:
+      encoded (bytes):
+        The x25519 public key to import.
+        It must be 32 bytes.
+
+    Returns:
+      :class:`Crypto.PublicKey.EccKey` : a new ECC key object.
+
+    Raises:
+      ValueError: when the given key cannot be parsed.
+    """
+
+    x = _import_curve25519_public_key(encoded)
+    return construct(curve='Curve25519', point_x=x)
+
+
+def import_x25519_private_key(encoded):
+    """Create a new X25519 private key object,
+    starting from the key encoded as raw ``bytes``,
+    in the format described in RFC7748.
+
+    Args:
+      encoded (bytes):
+        The X25519 private key to import.
+        It must be 32 bytes.
+
+    Returns:
+      :class:`Crypto.PublicKey.EccKey` : a new ECC key object.
+
+    Raises:
+      ValueError: when the given key cannot be parsed.
+    """
+
+    return construct(seed=encoded, curve="Curve25519")
+
+
 def key_agreement(**kwargs):
     """Perform a Diffie-Hellman key agreement.
 

lib/Crypto/Protocol/DH.pyi

@@ -12,4 +12,6 @@ class RequestParams(TypedDict, Generic[T]):
     eph_priv: NotRequired[EccKey]
     eph_pub: NotRequired[EccKey]
 
+def import_x25519_public_key(encoded: bytes) -> EccKey: ...
+def import_x25519_private_key(encoded: bytes) -> EccKey: ...
 def key_agreement(**kwargs: Unpack[RequestParams[T]]) -> T: ...