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# ===================================================================
#
# Copyright (c) 2022, Legrandin <helderijs@gmail.com>
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# ===================================================================
from Crypto.Math.Numbers import Integer
from Crypto.Hash import SHA512, SHAKE256
from Crypto.Util.py3compat import bchr, is_bytes
from Crypto.PublicKey.ECC import (EccKey,
construct,
_import_ed25519_public_key,
_import_ed448_public_key)
def import_public_key(encoded):
"""Create a new Ed25519 or Ed448 public key object,
starting from the key encoded as raw ``bytes``,
in the format described in RFC8032.
Args:
encoded (bytes):
The EdDSA public key to import.
It must be 32 bytes for Ed25519, and 57 bytes for Ed448.
Returns:
:class:`Crypto.PublicKey.EccKey` : a new ECC key object.
Raises:
ValueError: when the given key cannot be parsed.
"""
if len(encoded) == 32:
x, y = _import_ed25519_public_key(encoded)
curve_name = "Ed25519"
elif len(encoded) == 57:
x, y = _import_ed448_public_key(encoded)
curve_name = "Ed448"
else:
raise ValueError("Not an EdDSA key (%d bytes)" % len(encoded))
return construct(curve=curve_name, point_x=x, point_y=y)
def import_private_key(encoded):
"""Create a new Ed25519 or Ed448 private key object,
starting from the key encoded as raw ``bytes``,
in the format described in RFC8032.
Args:
encoded (bytes):
The EdDSA private key to import.
It must be 32 bytes for Ed25519, and 57 bytes for Ed448.
Returns:
:class:`Crypto.PublicKey.EccKey` : a new ECC key object.
Raises:
ValueError: when the given key cannot be parsed.
"""
if len(encoded) == 32:
curve_name = "ed25519"
elif len(encoded) == 57:
curve_name = "ed448"
else:
raise ValueError("Incorrect length. Only EdDSA private keys are supported.")
# Note that the private key is truly a sequence of random bytes,
# so we cannot check its correctness in any way.
return construct(seed=encoded, curve=curve_name)
class EdDSASigScheme(object):
"""An EdDSA signature object.
Do not instantiate directly.
Use :func:`Crypto.Signature.eddsa.new`.
"""
def __init__(self, key, context):
"""Create a new EdDSA object.
Do not instantiate this object directly,
use `Crypto.Signature.DSS.new` instead.
"""
self._key = key
self._context = context
self._A = key._export_eddsa()
self._order = key._curve.order
def can_sign(self):
"""Return ``True`` if this signature object can be used
for signing messages."""
return self._key.has_private()
def sign(self, msg_or_hash):
"""Compute the EdDSA signature of a message.
Args:
msg_or_hash (bytes or a hash object):
The message to sign (``bytes``, in case of *PureEdDSA*) or
the hash that was carried out over the message (hash object, for *HashEdDSA*).
The hash object must be :class:`Crypto.Hash.SHA512` for Ed25519,
and :class:`Crypto.Hash.SHAKE256` object for Ed448.
:return: The signature as ``bytes``. It is always 64 bytes for Ed25519, and 114 bytes for Ed448.
:raise TypeError: if the EdDSA key has no private half
"""
if not self._key.has_private():
raise TypeError("Private key is needed to sign")
if self._key._curve.name == "ed25519":
ph = isinstance(msg_or_hash, SHA512.SHA512Hash)
if not (ph or is_bytes(msg_or_hash)):
raise TypeError("'msg_or_hash' must be bytes of a SHA-512 hash")
eddsa_sign_method = self._sign_ed25519
elif self._key._curve.name == "ed448":
ph = isinstance(msg_or_hash, SHAKE256.SHAKE256_XOF)
if not (ph or is_bytes(msg_or_hash)):
raise TypeError("'msg_or_hash' must be bytes of a SHAKE256 hash")
eddsa_sign_method = self._sign_ed448
else:
raise ValueError("Incorrect curve for EdDSA")
return eddsa_sign_method(msg_or_hash, ph)
def _sign_ed25519(self, msg_or_hash, ph):
if self._context or ph:
flag = int(ph)
# dom2(flag, self._context)
dom2 = b'SigEd25519 no Ed25519 collisions' + bchr(flag) + \
bchr(len(self._context)) + self._context
else:
dom2 = b''
PHM = msg_or_hash.digest() if ph else msg_or_hash
# See RFC 8032, section 5.1.6
# Step 2
r_hash = SHA512.new(dom2 + self._key._prefix + PHM).digest()
r = Integer.from_bytes(r_hash, 'little') % self._order
# Step 3
R_pk = EccKey(point=r * self._key._curve.G)._export_eddsa()
# Step 4
k_hash = SHA512.new(dom2 + R_pk + self._A + PHM).digest()
k = Integer.from_bytes(k_hash, 'little') % self._order
# Step 5
s = (r + k * self._key.d) % self._order
return R_pk + s.to_bytes(32, 'little')
def _sign_ed448(self, msg_or_hash, ph):
flag = int(ph)
# dom4(flag, self._context)
dom4 = b'SigEd448' + bchr(flag) + \
bchr(len(self._context)) + self._context
PHM = msg_or_hash.read(64) if ph else msg_or_hash
# See RFC 8032, section 5.2.6
# Step 2
r_hash = SHAKE256.new(dom4 + self._key._prefix + PHM).read(114)
r = Integer.from_bytes(r_hash, 'little') % self._order
# Step 3
R_pk = EccKey(point=r * self._key._curve.G)._export_eddsa()
# Step 4
k_hash = SHAKE256.new(dom4 + R_pk + self._A + PHM).read(114)
k = Integer.from_bytes(k_hash, 'little') % self._order
# Step 5
s = (r + k * self._key.d) % self._order
return R_pk + s.to_bytes(57, 'little')
def verify(self, msg_or_hash, signature):
"""Check if an EdDSA signature is authentic.
Args:
msg_or_hash (bytes or a hash object):
The message to verify (``bytes``, in case of *PureEdDSA*) or
the hash that was carried out over the message (hash object, for *HashEdDSA*).
The hash object must be :class:`Crypto.Hash.SHA512` object for Ed25519,
and :class:`Crypto.Hash.SHAKE256` for Ed448.
signature (``bytes``):
The signature that needs to be validated.
It must be 64 bytes for Ed25519, and 114 bytes for Ed448.
:raise ValueError: if the signature is not authentic
"""
if self._key._curve.name == "ed25519":
ph = isinstance(msg_or_hash, SHA512.SHA512Hash)
if not (ph or is_bytes(msg_or_hash)):
raise TypeError("'msg_or_hash' must be bytes of a SHA-512 hash")
eddsa_verify_method = self._verify_ed25519
elif self._key._curve.name == "ed448":
ph = isinstance(msg_or_hash, SHAKE256.SHAKE256_XOF)
if not (ph or is_bytes(msg_or_hash)):
raise TypeError("'msg_or_hash' must be bytes of a SHAKE256 hash")
eddsa_verify_method = self._verify_ed448
else:
raise ValueError("Incorrect curve for EdDSA")
return eddsa_verify_method(msg_or_hash, signature, ph)
def _verify_ed25519(self, msg_or_hash, signature, ph):
if len(signature) != 64:
raise ValueError("The signature is not authentic (length)")
if self._context or ph:
flag = int(ph)
dom2 = b'SigEd25519 no Ed25519 collisions' + bchr(flag) + \
bchr(len(self._context)) + self._context
else:
dom2 = b''
PHM = msg_or_hash.digest() if ph else msg_or_hash
# Section 5.1.7
# Step 1
try:
R = import_public_key(signature[:32]).pointQ
except ValueError:
raise ValueError("The signature is not authentic (R)")
s = Integer.from_bytes(signature[32:], 'little')
if s > self._order:
raise ValueError("The signature is not authentic (S)")
# Step 2
k_hash = SHA512.new(dom2 + signature[:32] + self._A + PHM).digest()
k = Integer.from_bytes(k_hash, 'little') % self._order
# Step 3
point1 = s * 8 * self._key._curve.G
# OPTIMIZE: with double-scalar multiplication, with no SCA
# countermeasures because it is public values
point2 = 8 * R + k * 8 * self._key.pointQ
if point1 != point2:
raise ValueError("The signature is not authentic")
def _verify_ed448(self, msg_or_hash, signature, ph):
if len(signature) != 114:
raise ValueError("The signature is not authentic (length)")
flag = int(ph)
# dom4(flag, self._context)
dom4 = b'SigEd448' + bchr(flag) + \
bchr(len(self._context)) + self._context
PHM = msg_or_hash.read(64) if ph else msg_or_hash
# Section 5.2.7
# Step 1
try:
R = import_public_key(signature[:57]).pointQ
except ValueError:
raise ValueError("The signature is not authentic (R)")
s = Integer.from_bytes(signature[57:], 'little')
if s > self._order:
raise ValueError("The signature is not authentic (S)")
# Step 2
k_hash = SHAKE256.new(dom4 + signature[:57] + self._A + PHM).read(114)
k = Integer.from_bytes(k_hash, 'little') % self._order
# Step 3
point1 = s * 8 * self._key._curve.G
# OPTIMIZE: with double-scalar multiplication, with no SCA
# countermeasures because it is public values
point2 = 8 * R + k * 8 * self._key.pointQ
if point1 != point2:
raise ValueError("The signature is not authentic")
def new(key, mode, context=None):
"""Create a signature object :class:`EdDSASigScheme` that
can perform or verify an EdDSA signature.
Args:
key (:class:`Crypto.PublicKey.ECC` object):
The key to use for computing the signature (*private* keys only)
or for verifying one.
The key must be on the curve ``Ed25519`` or ``Ed448``.
mode (string):
This parameter must be ``'rfc8032'``.
context (bytes):
Up to 255 bytes of `context <https://datatracker.ietf.org/doc/html/rfc8032#page-41>`_,
which is a constant byte string to segregate different protocols or
different applications of the same key.
"""
if not isinstance(key, EccKey) or not key._is_eddsa():
raise ValueError("EdDSA can only be used with EdDSA keys")
if mode != 'rfc8032':
raise ValueError("Mode must be 'rfc8032'")
if context is None:
context = b''
elif len(context) > 255:
raise ValueError("Context for EdDSA must not be longer than 255 bytes")
return EdDSASigScheme(key, context)
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