344 lines
12 KiB
Python
344 lines
12 KiB
Python
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# ===================================================================
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#
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# Copyright (c) 2022, Legrandin <helderijs@gmail.com>
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# All rights reserved.
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#
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# Redistribution and use in source and binary forms, with or without
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# modification, are permitted provided that the following conditions
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# are met:
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#
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# 1. Redistributions of source code must retain the above copyright
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# notice, this list of conditions and the following disclaimer.
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# 2. Redistributions in binary form must reproduce the above copyright
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# notice, this list of conditions and the following disclaimer in
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# the documentation and/or other materials provided with the
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# distribution.
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#
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# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
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# FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
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# COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
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# INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
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# BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
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# LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
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# CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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# LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
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# ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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# POSSIBILITY OF SUCH DAMAGE.
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# ===================================================================
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from Cryptodome.Math.Numbers import Integer
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from Cryptodome.Hash import SHA512, SHAKE256
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from Cryptodome.Util.py3compat import bchr, is_bytes
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from Cryptodome.PublicKey.ECC import (EccKey,
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construct,
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_import_ed25519_public_key,
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_import_ed448_public_key)
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def import_public_key(encoded):
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"""Create a new Ed25519 or Ed448 public key object,
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starting from the key encoded as raw ``bytes``,
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in the format described in RFC8032.
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Args:
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encoded (bytes):
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The EdDSA public key to import.
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It must be 32 bytes for Ed25519, and 57 bytes for Ed448.
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Returns:
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:class:`Cryptodome.PublicKey.EccKey` : a new ECC key object.
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Raises:
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ValueError: when the given key cannot be parsed.
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"""
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if len(encoded) == 32:
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x, y = _import_ed25519_public_key(encoded)
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curve_name = "Ed25519"
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elif len(encoded) == 57:
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x, y = _import_ed448_public_key(encoded)
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curve_name = "Ed448"
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else:
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raise ValueError("Not an EdDSA key (%d bytes)" % len(encoded))
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return construct(curve=curve_name, point_x=x, point_y=y)
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def import_private_key(encoded):
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"""Create a new Ed25519 or Ed448 private key object,
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starting from the key encoded as raw ``bytes``,
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in the format described in RFC8032.
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Args:
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encoded (bytes):
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The EdDSA private key to import.
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It must be 32 bytes for Ed25519, and 57 bytes for Ed448.
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Returns:
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:class:`Cryptodome.PublicKey.EccKey` : a new ECC key object.
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Raises:
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ValueError: when the given key cannot be parsed.
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"""
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if len(encoded) == 32:
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curve_name = "ed25519"
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elif len(encoded) == 57:
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curve_name = "ed448"
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else:
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raise ValueError("Incorrect length. Only EdDSA private keys are supported.")
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# Note that the private key is truly a sequence of random bytes,
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# so we cannot check its correctness in any way.
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return construct(seed=encoded, curve=curve_name)
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class EdDSASigScheme(object):
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"""An EdDSA signature object.
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Do not instantiate directly.
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Use :func:`Cryptodome.Signature.eddsa.new`.
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"""
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def __init__(self, key, context):
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"""Create a new EdDSA object.
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Do not instantiate this object directly,
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use `Cryptodome.Signature.DSS.new` instead.
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"""
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self._key = key
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self._context = context
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self._A = key._export_eddsa()
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self._order = key._curve.order
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def can_sign(self):
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"""Return ``True`` if this signature object can be used
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for signing messages."""
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return self._key.has_private()
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def sign(self, msg_or_hash):
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"""Compute the EdDSA signature of a message.
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Args:
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msg_or_hash (bytes or a hash object):
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The message to sign (``bytes``, in case of *PureEdDSA*) or
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the hash that was carried out over the message (hash object, for *HashEdDSA*).
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The hash object must be :class:`Cryptodome.Hash.SHA512` for Ed25519,
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and :class:`Cryptodome.Hash.SHAKE256` object for Ed448.
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:return: The signature as ``bytes``. It is always 64 bytes for Ed25519, and 114 bytes for Ed448.
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:raise TypeError: if the EdDSA key has no private half
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"""
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if not self._key.has_private():
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raise TypeError("Private key is needed to sign")
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if self._key._curve.name == "ed25519":
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ph = isinstance(msg_or_hash, SHA512.SHA512Hash)
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if not (ph or is_bytes(msg_or_hash)):
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raise TypeError("'msg_or_hash' must be bytes of a SHA-512 hash")
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eddsa_sign_method = self._sign_ed25519
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elif self._key._curve.name == "ed448":
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ph = isinstance(msg_or_hash, SHAKE256.SHAKE256_XOF)
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if not (ph or is_bytes(msg_or_hash)):
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raise TypeError("'msg_or_hash' must be bytes of a SHAKE256 hash")
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eddsa_sign_method = self._sign_ed448
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else:
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raise ValueError("Incorrect curve for EdDSA")
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return eddsa_sign_method(msg_or_hash, ph)
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def _sign_ed25519(self, msg_or_hash, ph):
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if self._context or ph:
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flag = int(ph)
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# dom2(flag, self._context)
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dom2 = b'SigEd25519 no Ed25519 collisions' + bchr(flag) + \
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bchr(len(self._context)) + self._context
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else:
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dom2 = b''
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PHM = msg_or_hash.digest() if ph else msg_or_hash
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# See RFC 8032, section 5.1.6
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# Step 2
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r_hash = SHA512.new(dom2 + self._key._prefix + PHM).digest()
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r = Integer.from_bytes(r_hash, 'little') % self._order
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# Step 3
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R_pk = EccKey(point=r * self._key._curve.G)._export_eddsa()
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# Step 4
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k_hash = SHA512.new(dom2 + R_pk + self._A + PHM).digest()
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k = Integer.from_bytes(k_hash, 'little') % self._order
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# Step 5
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s = (r + k * self._key.d) % self._order
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return R_pk + s.to_bytes(32, 'little')
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def _sign_ed448(self, msg_or_hash, ph):
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flag = int(ph)
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# dom4(flag, self._context)
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dom4 = b'SigEd448' + bchr(flag) + \
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bchr(len(self._context)) + self._context
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PHM = msg_or_hash.read(64) if ph else msg_or_hash
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# See RFC 8032, section 5.2.6
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# Step 2
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r_hash = SHAKE256.new(dom4 + self._key._prefix + PHM).read(114)
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r = Integer.from_bytes(r_hash, 'little') % self._order
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# Step 3
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R_pk = EccKey(point=r * self._key._curve.G)._export_eddsa()
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# Step 4
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k_hash = SHAKE256.new(dom4 + R_pk + self._A + PHM).read(114)
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k = Integer.from_bytes(k_hash, 'little') % self._order
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# Step 5
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s = (r + k * self._key.d) % self._order
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return R_pk + s.to_bytes(57, 'little')
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def verify(self, msg_or_hash, signature):
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"""Check if an EdDSA signature is authentic.
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Args:
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msg_or_hash (bytes or a hash object):
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The message to verify (``bytes``, in case of *PureEdDSA*) or
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the hash that was carried out over the message (hash object, for *HashEdDSA*).
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The hash object must be :class:`Cryptodome.Hash.SHA512` object for Ed25519,
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and :class:`Cryptodome.Hash.SHAKE256` for Ed448.
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signature (``bytes``):
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The signature that needs to be validated.
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It must be 64 bytes for Ed25519, and 114 bytes for Ed448.
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:raise ValueError: if the signature is not authentic
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"""
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if self._key._curve.name == "ed25519":
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ph = isinstance(msg_or_hash, SHA512.SHA512Hash)
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if not (ph or is_bytes(msg_or_hash)):
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raise TypeError("'msg_or_hash' must be bytes of a SHA-512 hash")
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eddsa_verify_method = self._verify_ed25519
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elif self._key._curve.name == "ed448":
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ph = isinstance(msg_or_hash, SHAKE256.SHAKE256_XOF)
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if not (ph or is_bytes(msg_or_hash)):
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raise TypeError("'msg_or_hash' must be bytes of a SHAKE256 hash")
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eddsa_verify_method = self._verify_ed448
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else:
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raise ValueError("Incorrect curve for EdDSA")
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return eddsa_verify_method(msg_or_hash, signature, ph)
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def _verify_ed25519(self, msg_or_hash, signature, ph):
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if len(signature) != 64:
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raise ValueError("The signature is not authentic (length)")
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if self._context or ph:
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flag = int(ph)
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dom2 = b'SigEd25519 no Ed25519 collisions' + bchr(flag) + \
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bchr(len(self._context)) + self._context
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else:
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dom2 = b''
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PHM = msg_or_hash.digest() if ph else msg_or_hash
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# Section 5.1.7
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# Step 1
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try:
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R = import_public_key(signature[:32]).pointQ
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except ValueError:
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raise ValueError("The signature is not authentic (R)")
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s = Integer.from_bytes(signature[32:], 'little')
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if s > self._order:
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raise ValueError("The signature is not authentic (S)")
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# Step 2
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k_hash = SHA512.new(dom2 + signature[:32] + self._A + PHM).digest()
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k = Integer.from_bytes(k_hash, 'little') % self._order
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# Step 3
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point1 = s * 8 * self._key._curve.G
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# OPTIMIZE: with double-scalar multiplication, with no SCA
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# countermeasures because it is public values
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point2 = 8 * R + k * 8 * self._key.pointQ
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if point1 != point2:
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raise ValueError("The signature is not authentic")
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def _verify_ed448(self, msg_or_hash, signature, ph):
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if len(signature) != 114:
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raise ValueError("The signature is not authentic (length)")
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flag = int(ph)
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# dom4(flag, self._context)
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dom4 = b'SigEd448' + bchr(flag) + \
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bchr(len(self._context)) + self._context
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PHM = msg_or_hash.read(64) if ph else msg_or_hash
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# Section 5.2.7
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# Step 1
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try:
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R = import_public_key(signature[:57]).pointQ
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except ValueError:
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raise ValueError("The signature is not authentic (R)")
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s = Integer.from_bytes(signature[57:], 'little')
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if s > self._order:
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raise ValueError("The signature is not authentic (S)")
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# Step 2
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k_hash = SHAKE256.new(dom4 + signature[:57] + self._A + PHM).read(114)
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k = Integer.from_bytes(k_hash, 'little') % self._order
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# Step 3
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point1 = s * 8 * self._key._curve.G
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# OPTIMIZE: with double-scalar multiplication, with no SCA
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# countermeasures because it is public values
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point2 = 8 * R + k * 8 * self._key.pointQ
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if point1 != point2:
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raise ValueError("The signature is not authentic")
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def new(key, mode, context=None):
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"""Create a signature object :class:`EdDSASigScheme` that
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can perform or verify an EdDSA signature.
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Args:
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key (:class:`Cryptodome.PublicKey.ECC` object):
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The key to use for computing the signature (*private* keys only)
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or for verifying one.
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The key must be on the curve ``Ed25519`` or ``Ed448``.
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mode (string):
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This parameter must be ``'rfc8032'``.
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context (bytes):
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Up to 255 bytes of `context <https://datatracker.ietf.org/doc/html/rfc8032#page-41>`_,
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which is a constant byte string to segregate different protocols or
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different applications of the same key.
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"""
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if not isinstance(key, EccKey) or not key._is_eddsa():
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raise ValueError("EdDSA can only be used with EdDSA keys")
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if mode != 'rfc8032':
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raise ValueError("Mode must be 'rfc8032'")
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if context is None:
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context = b''
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elif len(context) > 255:
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raise ValueError("Context for EdDSA must not be longer than 255 bytes")
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return EdDSASigScheme(key, context)
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