Blind signature support in pyelliptic
- add blind signature functionality to pyelliptic as described in #1409 - add tests for blind signatures - PEP8 fixes for pyelliptic - some minor refactoring is necessary for further integration, this is just a minimal implementation to pass a testpython3android
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#!/usr/bin/env python
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"""
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ECC blind signature functionality based on "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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# pylint: disable=invalid-name
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from .openssl import OpenSSL
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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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def __init__(self, curve="secp256k1"):
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self.group = OpenSSL.EC_GROUP_new_by_curve_name(OpenSSL.get_curve(curve))
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self.ctx = OpenSSL.BN_CTX_new()
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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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# 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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# Generator G
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self.G = OpenSSL.EC_GROUP_get0_generator(self.group)
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# Certifier's pubkey
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self.pubkey = (self.group, self.G, self.n)
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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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def create_signing_request(self, msg):
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"""
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Requester creates a new signing request
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"""
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# new keypair
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self.keypair = ECCBlind.ec_gen_keypair(self.group, self.ctx)
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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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self.Q = self.keypair[1]
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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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x0 = OpenSSL.BN_new()
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y0 = OpenSSL.BN_new()
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OpenSSL.EC_POINT_get_affine_coordinates_GFp(self.group, self.F, x0, y0,
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self.ctx)
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self.r = x0
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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(msg, len(msg), 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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def blind_sign(self):
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"""
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Signer blind-signs the request
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"""
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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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def unblind(self):
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"""
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Requester unblinds the signature
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"""
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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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def verify(self):
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"""
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Verify signature with certifier's pubkey
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"""
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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, self.signature[0], 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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else:
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return retval == 0
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@ -0,0 +1,22 @@
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"""
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Test for ECC blind signatures
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"""
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import os
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import unittest
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from src.pyelliptic.eccblind import ECCBlind
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class TestBlindSig(unittest.TestCase):
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"""
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Test case for ECC blind signature
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"""
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def test_blind_sig(self):
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"""Test full sequence using a random certifier key and a random message"""
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blind_sig = ECCBlind()
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blind_sig.signer_init()
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msg = os.urandom(64)
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blind_sig.create_signing_request(msg)
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blind_sig.blind_sign()
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blind_sig.unblind()
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self.assertTrue(blind_sig.verify())
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