281 lines
8.0 KiB
Python
281 lines
8.0 KiB
Python
#!/usr/bin/env python
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"""
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ECC blind signature functionality based on
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"An Efficient Blind Signature Scheme
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Based on the Elliptic CurveDiscrete Logarithm Problem" by Morteza Nikooghadama
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<mnikooghadam@sbu.ac.ir> and Ali Zakerolhosseini <a-zaker@sbu.ac.ir>,
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http://www.isecure-journal.com/article_39171_47f9ec605dd3918c2793565ec21fcd7a.pdf
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"""
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# variable names are based on the math in the paper, so they don't conform
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# to PEP8
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from hashlib import sha256
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import time
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try:
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import msgpack
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except ImportError:
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try:
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import umsgpack as msgpack
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except ImportError:
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import fallback.umsgpack.umsgpack as msgpack
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from .openssl import OpenSSL
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class Metadata(object):
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"""
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Pubkey metadata
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"""
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def __init__(self, exp=0, value=0):
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self.exp = 0
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self.value = 0
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if exp:
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self.exp = exp
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if value:
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self.value = value
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def serialize(self):
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if self.exp or self.value:
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return [self.exp, self.value]
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else:
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return []
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@staticmethod
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def deserialize(self, data):
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exp, value = data
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return Medatadata(exp, value)
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def verify(self, value):
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if self.value and value > self.value:
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return False
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if self.exp:
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if time.time() > self.exp:
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return False
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return True
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class ECCBlind(object): # pylint: disable=too-many-instance-attributes
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"""
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Class for ECC blind signature functionality
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"""
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# init
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k = None
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R = None
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keypair = None
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F = None
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Q = None
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a = None
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b = None
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c = None
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binv = None
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r = None
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m = None
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m_ = None
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s_ = None
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signature = None
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@staticmethod
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def ec_get_random(group, ctx):
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"""
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Random point from finite field
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"""
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order = OpenSSL.BN_new()
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OpenSSL.EC_GROUP_get_order(group, order, ctx)
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OpenSSL.BN_rand(order, OpenSSL.BN_num_bits(order), 0, 0)
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return order
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@staticmethod
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def ec_invert(group, a, ctx):
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"""
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ECC inversion
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"""
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order = OpenSSL.BN_new()
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OpenSSL.EC_GROUP_get_order(group, order, ctx)
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inverse = OpenSSL.BN_mod_inverse(0, a, order, ctx)
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return inverse
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@staticmethod
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def ec_gen_keypair(group, ctx):
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"""
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Generate an ECC keypair
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"""
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d = ECCBlind.ec_get_random(group, ctx)
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Q = OpenSSL.EC_POINT_new(group)
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OpenSSL.EC_POINT_mul(group, Q, d, 0, 0, 0)
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return (d, Q)
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@staticmethod
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def ec_Ftor(F, group, ctx):
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"""
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x0 coordinate of F
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"""
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# F = (x0, y0)
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x0 = OpenSSL.BN_new()
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y0 = OpenSSL.BN_new()
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OpenSSL.EC_POINT_get_affine_coordinates_GFp(group, F, x0, y0, ctx)
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return x0
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@staticmethod
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def deserialize(self, data):
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pubkey_deserialized, meta = msgpack.unpackb(data)
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if meta:
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obj = ECCBlind(pubkey=pubkey_deserialized, metadata=meta)
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else:
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obj = ECCBlind(pubkey=pubkey_deserialized)
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return obj
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def serialize(self):
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data = (self.pubkey, self.metadata.serialize)
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retval = msgpack.packb(data)
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return retval
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def __init__(self, curve="secp256k1", pubkey=None, metadata=None):
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self.ctx = OpenSSL.BN_CTX_new()
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if pubkey:
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self.group, self.G, self.n, self.Q = pubkey
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else:
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self.group = OpenSSL.EC_GROUP_new_by_curve_name(
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OpenSSL.get_curve(curve))
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# Order n
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self.n = OpenSSL.BN_new()
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OpenSSL.EC_GROUP_get_order(self.group, self.n, self.ctx)
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# Generator G
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self.G = OpenSSL.EC_GROUP_get0_generator(self.group)
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# new keypair
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self.keypair = ECCBlind.ec_gen_keypair(self.group, self.ctx)
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self.Q = self.keypair[1]
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self.pubkey = (self.group, self.G, self.n, self.Q)
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# Identity O (infinity)
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self.iO = OpenSSL.EC_POINT_new(self.group)
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OpenSSL.EC_POINT_set_to_infinity(self.group, self.iO)
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if metadata:
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self._set_metadata(self, metadata)
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else:
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self.metadata = Metadata()
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def _set_metadata(self, metadata):
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self.metadata = Metadata.deserialise(metadata)
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def signer_init(self):
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"""
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Init signer
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"""
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# Signer: Random integer k
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self.k = ECCBlind.ec_get_random(self.group, self.ctx)
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# R = kG
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self.R = OpenSSL.EC_POINT_new(self.group)
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OpenSSL.EC_POINT_mul(self.group, self.R, self.k, 0, 0, 0)
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return self.R
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def create_signing_request(self, R, msg):
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"""
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Requester creates a new signing request
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"""
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self.R = R
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msghash = sha256(msg)
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# Requester: 3 random blinding factors
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self.F = OpenSSL.EC_POINT_new(self.group)
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OpenSSL.EC_POINT_set_to_infinity(self.group, self.F)
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temp = OpenSSL.EC_POINT_new(self.group)
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abinv = OpenSSL.BN_new()
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# F != O
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while OpenSSL.EC_POINT_cmp(self.group, self.F, self.iO, self.ctx) == 0:
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self.a = ECCBlind.ec_get_random(self.group, self.ctx)
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self.b = ECCBlind.ec_get_random(self.group, self.ctx)
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self.c = ECCBlind.ec_get_random(self.group, self.ctx)
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# F = b^-1 * R...
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self.binv = ECCBlind.ec_invert(self.group, self.b, self.ctx)
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OpenSSL.EC_POINT_mul(self.group, temp, 0, self.R, self.binv, 0)
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OpenSSL.EC_POINT_copy(self.F, temp)
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# ... + a*b^-1 * Q...
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OpenSSL.BN_mul(abinv, self.a, self.binv, self.ctx)
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OpenSSL.EC_POINT_mul(self.group, temp, 0, self.Q, abinv, 0)
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OpenSSL.EC_POINT_add(self.group, self.F, self.F, temp, 0)
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# ... + c*G
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OpenSSL.EC_POINT_mul(self.group, temp, 0, self.G, self.c, 0)
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OpenSSL.EC_POINT_add(self.group, self.F, self.F, temp, 0)
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# F = (x0, y0)
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self.r = ECCBlind.ec_Ftor(self.F, self.group, self.ctx)
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# Requester: Blinding (m' = br(m) + a)
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self.m = OpenSSL.BN_new()
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OpenSSL.BN_bin2bn(msghash, len(msghash), self.m)
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self.m_ = OpenSSL.BN_new()
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OpenSSL.BN_mod_mul(self.m_, self.b, self.r, self.n, self.ctx)
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OpenSSL.BN_mod_mul(self.m_, self.m_, self.m, self.n, self.ctx)
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OpenSSL.BN_mod_add(self.m_, self.m_, self.a, self.n, self.ctx)
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return self.m_
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def blind_sign(self, m_):
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"""
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Signer blind-signs the request
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"""
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self.m_ = m_
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self.s_ = OpenSSL.BN_new()
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OpenSSL.BN_mod_mul(self.s_, self.keypair[0], self.m_, self.n, self.ctx)
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OpenSSL.BN_mod_add(self.s_, self.s_, self.k, self.n, self.ctx)
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return self.s_
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def unblind(self, s_):
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"""
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Requester unblinds the signature
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"""
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self.s_ = s_
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s = OpenSSL.BN_new()
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OpenSSL.BN_mod_mul(s, self.binv, self.s_, self.n, self.ctx)
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OpenSSL.BN_mod_add(s, s, self.c, self.n, self.ctx)
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self.signature = (s, self.F)
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return self.signature
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def verify(self, msg, signature, value=0):
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"""
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Verify signature with certifier's pubkey
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"""
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# convert msg to BIGNUM
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self.m = OpenSSL.BN_new()
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msghash = sha256(msg)
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OpenSSL.BN_bin2bn(msghash, len(msghash), self.m)
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# init
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s, self.F = signature
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if self.r is None:
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self.r = ECCBlind.ec_Ftor(self.F, self.group, self.ctx)
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lhs = OpenSSL.EC_POINT_new(self.group)
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rhs = OpenSSL.EC_POINT_new(self.group)
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OpenSSL.EC_POINT_mul(self.group, lhs, s, 0, 0, 0)
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OpenSSL.EC_POINT_mul(self.group, rhs, 0, self.Q, self.m, 0)
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OpenSSL.EC_POINT_mul(self.group, rhs, 0, rhs, self.r, 0)
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OpenSSL.EC_POINT_add(self.group, rhs, rhs, self.F, self.ctx)
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retval = OpenSSL.EC_POINT_cmp(self.group, lhs, rhs, self.ctx)
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if retval == -1:
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raise RuntimeError("EC_POINT_cmp returned an error")
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elif retval != 0:
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return False
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elif self.metadata:
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return self.metadata.verify(value)
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return True
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