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 test
This commit is contained in:
Peter Šurda 2019-08-26 17:46:25 +02:00
parent f180b1a5b0
commit 2e0f7755c6
Signed by: PeterSurda
GPG Key ID: 0C5F50C0B5F37D87
7 changed files with 394 additions and 51 deletions

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@ -2,18 +2,20 @@
# Author: Yann GUIBET
# Contact: <yannguibet@gmail.com>
from .openssl import OpenSSL
from .ecc import ECC
from .eccblind import ECCBlind
from .cipher import Cipher
from .hash import hmac_sha256, hmac_sha512, pbkdf2
__version__ = '1.3'
__all__ = [
'OpenSSL',
'ECC',
'ECCBlind',
'Cipher',
'hmac_sha256',
'hmac_sha512',
'pbkdf2'
]
from .openssl import OpenSSL
from .ecc import ECC
from .cipher import Cipher
from .hash import hmac_sha256, hmac_sha512, pbkdf2

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@ -4,7 +4,7 @@
# Copyright (C) 2011 Yann GUIBET <yannguibet@gmail.com>
# See LICENSE for details.
from pyelliptic.openssl import OpenSSL
from openssl import OpenSSL
class Cipher:

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@ -12,9 +12,9 @@ src/pyelliptic/ecc.py
from hashlib import sha512
from struct import pack, unpack
from pyelliptic.cipher import Cipher
from pyelliptic.hash import equals, hmac_sha256
from pyelliptic.openssl import OpenSSL
from cipher import Cipher
from hash import equals, hmac_sha256
from openssl import OpenSSL
class ECC(object):

179
src/pyelliptic/eccblind.py Normal file
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@ -0,0 +1,179 @@
#!/usr/bin/env python
"""
ECC blind signature functionality based on "An Efficient Blind Signature Scheme
Based on the Elliptic CurveDiscrete Logarithm Problem" by Morteza Nikooghadama
<mnikooghadam@sbu.ac.ir> and Ali Zakerolhosseini <a-zaker@sbu.ac.ir>,
http://www.isecure-journal.com/article_39171_47f9ec605dd3918c2793565ec21fcd7a.pdf
"""
# variable names are based on the math in the paper, so they don't conform
# to PEP8
# pylint: disable=invalid-name
from .openssl import OpenSSL
class ECCBlind(object): # pylint: disable=too-many-instance-attributes
"""
Class for ECC blind signature functionality
"""
# init
k = None
R = None
keypair = None
F = None
Q = None
a = None
b = None
c = None
binv = None
r = None
m = None
m_ = None
s_ = None
signature = None
@staticmethod
def ec_get_random(group, ctx):
"""
Random point from finite field
"""
order = OpenSSL.BN_new()
OpenSSL.EC_GROUP_get_order(group, order, ctx)
OpenSSL.BN_rand(order, OpenSSL.BN_num_bits(order), 0, 0)
return order
@staticmethod
def ec_invert(group, a, ctx):
"""
ECC inversion
"""
order = OpenSSL.BN_new()
OpenSSL.EC_GROUP_get_order(group, order, ctx)
inverse = OpenSSL.BN_mod_inverse(0, a, order, ctx)
return inverse
@staticmethod
def ec_gen_keypair(group, ctx):
"""
Generate an ECC keypair
"""
d = ECCBlind.ec_get_random(group, ctx)
Q = OpenSSL.EC_POINT_new(group)
OpenSSL.EC_POINT_mul(group, Q, d, 0, 0, 0)
return (d, Q)
def __init__(self, curve="secp256k1"):
self.group = OpenSSL.EC_GROUP_new_by_curve_name(OpenSSL.get_curve(curve))
self.ctx = OpenSSL.BN_CTX_new()
# Order n
self.n = OpenSSL.BN_new()
OpenSSL.EC_GROUP_get_order(self.group, self.n, self.ctx)
# Identity O (infinity)
self.iO = OpenSSL.EC_POINT_new(self.group)
OpenSSL.EC_POINT_set_to_infinity(self.group, self.iO)
# Generator G
self.G = OpenSSL.EC_GROUP_get0_generator(self.group)
# Certifier's pubkey
self.pubkey = (self.group, self.G, self.n)
def signer_init(self):
"""
Init signer
"""
# Signer: Random integer k
self.k = ECCBlind.ec_get_random(self.group, self.ctx)
# R = kG
self.R = OpenSSL.EC_POINT_new(self.group)
OpenSSL.EC_POINT_mul(self.group, self.R, self.k, 0, 0, 0)
def create_signing_request(self, msg):
"""
Requester creates a new signing request
"""
# new keypair
self.keypair = ECCBlind.ec_gen_keypair(self.group, self.ctx)
# Requester: 3 random blinding factors
self.F = OpenSSL.EC_POINT_new(self.group)
OpenSSL.EC_POINT_set_to_infinity(self.group, self.F)
temp = OpenSSL.EC_POINT_new(self.group)
self.Q = self.keypair[1]
abinv = OpenSSL.BN_new()
# F != O
while OpenSSL.EC_POINT_cmp(self.group, self.F, self.iO, self.ctx) == 0:
self.a = ECCBlind.ec_get_random(self.group, self.ctx)
self.b = ECCBlind.ec_get_random(self.group, self.ctx)
self.c = ECCBlind.ec_get_random(self.group, self.ctx)
# F = b^-1 * R...
self.binv = ECCBlind.ec_invert(self.group, self.b, self.ctx)
OpenSSL.EC_POINT_mul(self.group, temp, 0, self.R, self.binv, 0)
OpenSSL.EC_POINT_copy(self.F, temp)
# ... + a*b^-1 * Q...
OpenSSL.BN_mul(abinv, self.a, self.binv, self.ctx)
OpenSSL.EC_POINT_mul(self.group, temp, 0, self.Q, abinv, 0)
OpenSSL.EC_POINT_add(self.group, self.F, self.F, temp, 0)
# ... + c*G
OpenSSL.EC_POINT_mul(self.group, temp, 0, self.G, self.c, 0)
OpenSSL.EC_POINT_add(self.group, self.F, self.F, temp, 0)
# F = (x0, y0)
x0 = OpenSSL.BN_new()
y0 = OpenSSL.BN_new()
OpenSSL.EC_POINT_get_affine_coordinates_GFp(self.group, self.F, x0, y0,
self.ctx)
self.r = x0
# Requester: Blinding (m' = br(m) + a)
self.m = OpenSSL.BN_new()
OpenSSL.BN_bin2bn(msg, len(msg), self.m)
self.m_ = OpenSSL.BN_new()
OpenSSL.BN_mod_mul(self.m_, self.b, self.r, self.n, self.ctx)
OpenSSL.BN_mod_mul(self.m_, self.m_, self.m, self.n, self.ctx)
OpenSSL.BN_mod_add(self.m_, self.m_, self.a, self.n, self.ctx)
def blind_sign(self):
"""
Signer blind-signs the request
"""
self.s_ = OpenSSL.BN_new()
OpenSSL.BN_mod_mul(self.s_, self.keypair[0], self.m_, self.n, self.ctx)
OpenSSL.BN_mod_add(self.s_, self.s_, self.k, self.n, self.ctx)
def unblind(self):
"""
Requester unblinds the signature
"""
s = OpenSSL.BN_new()
OpenSSL.BN_mod_mul(s, self.binv, self.s_, self.n, self.ctx)
OpenSSL.BN_mod_add(s, s, self.c, self.n, self.ctx)
self.signature = (s, self.F)
def verify(self):
"""
Verify signature with certifier's pubkey
"""
lhs = OpenSSL.EC_POINT_new(self.group)
rhs = OpenSSL.EC_POINT_new(self.group)
OpenSSL.EC_POINT_mul(self.group, lhs, self.signature[0], 0, 0, 0)
OpenSSL.EC_POINT_mul(self.group, rhs, 0, self.Q, self.m, 0)
OpenSSL.EC_POINT_mul(self.group, rhs, 0, rhs, self.r, 0)
OpenSSL.EC_POINT_add(self.group, rhs, rhs, self.F, self.ctx)
retval = OpenSSL.EC_POINT_cmp(self.group, lhs, rhs, self.ctx)
if retval == -1:
raise RuntimeError("EC_POINT_cmp returned an error")
else:
return retval == 0

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@ -4,7 +4,7 @@
# Copyright (C) 2011 Yann GUIBET <yannguibet@gmail.com>
# See LICENSE for details.
from pyelliptic.openssl import OpenSSL
from openssl import OpenSSL
# For python3

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@ -19,7 +19,9 @@ class CipherName:
self._blocksize = blocksize
def __str__(self):
return "Cipher : " + self._name + " | Blocksize : " + str(self._blocksize) + " | Fonction pointer : " + str(self._pointer)
return "Cipher : " + self._name + \
" | Blocksize : " + str(self._blocksize) + \
" | Function pointer : " + str(self._pointer)
def get_pointer(self):
return self._pointer()
@ -36,7 +38,7 @@ def get_version(library):
hexversion = None
cflags = None
try:
#OpenSSL 1.1
# OpenSSL 1.1
OPENSSL_VERSION = 0
OPENSSL_CFLAGS = 1
library.OpenSSL_version.argtypes = [ctypes.c_int]
@ -47,7 +49,7 @@ def get_version(library):
hexversion = library.OpenSSL_version_num()
except AttributeError:
try:
#OpenSSL 1.0
# OpenSSL 1.0
SSLEAY_VERSION = 0
SSLEAY_CFLAGS = 2
library.SSLeay.restype = ctypes.c_long
@ -57,7 +59,7 @@ def get_version(library):
cflags = library.SSLeay_version(SSLEAY_CFLAGS)
hexversion = library.SSLeay()
except AttributeError:
#raise NotImplementedError('Cannot determine version of this OpenSSL library.')
# raise NotImplementedError('Cannot determine version of this OpenSSL library.')
pass
return (version, hexversion, cflags)
@ -130,7 +132,11 @@ class _OpenSSL:
self.EC_POINT_get_affine_coordinates_GFp = self._lib.EC_POINT_get_affine_coordinates_GFp
self.EC_POINT_get_affine_coordinates_GFp.restype = ctypes.c_int
self.EC_POINT_get_affine_coordinates_GFp.argtypes = [ctypes.c_void_p, ctypes.c_void_p, ctypes.c_void_p, ctypes.c_void_p, ctypes.c_void_p]
self.EC_POINT_get_affine_coordinates_GFp.argtypes = [ctypes.c_void_p,
ctypes.c_void_p,
ctypes.c_void_p,
ctypes.c_void_p,
ctypes.c_void_p]
self.EC_KEY_set_private_key = self._lib.EC_KEY_set_private_key
self.EC_KEY_set_private_key.restype = ctypes.c_int
@ -144,11 +150,16 @@ class _OpenSSL:
self.EC_KEY_set_group = self._lib.EC_KEY_set_group
self.EC_KEY_set_group.restype = ctypes.c_int
self.EC_KEY_set_group.argtypes = [ctypes.c_void_p, ctypes.c_void_p]
self.EC_KEY_set_group.argtypes = [ctypes.c_void_p,
ctypes.c_void_p]
self.EC_POINT_set_affine_coordinates_GFp = self._lib.EC_POINT_set_affine_coordinates_GFp
self.EC_POINT_set_affine_coordinates_GFp.restype = ctypes.c_int
self.EC_POINT_set_affine_coordinates_GFp.argtypes = [ctypes.c_void_p, ctypes.c_void_p, ctypes.c_void_p, ctypes.c_void_p, ctypes.c_void_p]
self.EC_POINT_set_affine_coordinates_GFp.argtypes = [ctypes.c_void_p,
ctypes.c_void_p,
ctypes.c_void_p,
ctypes.c_void_p,
ctypes.c_void_p]
self.EC_POINT_new = self._lib.EC_POINT_new
self.EC_POINT_new.restype = ctypes.c_void_p
@ -164,7 +175,11 @@ class _OpenSSL:
self.EC_POINT_mul = self._lib.EC_POINT_mul
self.EC_POINT_mul.restype = None
self.EC_POINT_mul.argtypes = [ctypes.c_void_p, ctypes.c_void_p, ctypes.c_void_p, ctypes.c_void_p, ctypes.c_void_p]
self.EC_POINT_mul.argtypes = [ctypes.c_void_p,
ctypes.c_void_p,
ctypes.c_void_p,
ctypes.c_void_p,
ctypes.c_void_p]
self.EC_KEY_set_private_key = self._lib.EC_KEY_set_private_key
self.EC_KEY_set_private_key.restype = ctypes.c_int
@ -178,7 +193,8 @@ class _OpenSSL:
self.EC_KEY_set_method = self._lib.EC_KEY_set_method
self._lib.EC_KEY_set_method.restype = ctypes.c_int
self._lib.EC_KEY_set_method.argtypes = [ctypes.c_void_p, ctypes.c_void_p]
self._lib.EC_KEY_set_method.argtypes = [ctypes.c_void_p,
ctypes.c_void_p]
else:
self.ECDH_OpenSSL = self._lib.ECDH_OpenSSL
self._lib.ECDH_OpenSSL.restype = ctypes.c_void_p
@ -186,7 +202,8 @@ class _OpenSSL:
self.ECDH_set_method = self._lib.ECDH_set_method
self._lib.ECDH_set_method.restype = ctypes.c_int
self._lib.ECDH_set_method.argtypes = [ctypes.c_void_p, ctypes.c_void_p]
self._lib.ECDH_set_method.argtypes = [ctypes.c_void_p,
ctypes.c_void_p]
self.BN_CTX_new = self._lib.BN_CTX_new
self._lib.BN_CTX_new.restype = ctypes.c_void_p
@ -195,12 +212,15 @@ class _OpenSSL:
self.ECDH_compute_key = self._lib.ECDH_compute_key
self.ECDH_compute_key.restype = ctypes.c_int
self.ECDH_compute_key.argtypes = [ctypes.c_void_p,
ctypes.c_int, ctypes.c_void_p, ctypes.c_void_p]
ctypes.c_int,
ctypes.c_void_p,
ctypes.c_void_p]
self.EVP_CipherInit_ex = self._lib.EVP_CipherInit_ex
self.EVP_CipherInit_ex.restype = ctypes.c_int
self.EVP_CipherInit_ex.argtypes = [ctypes.c_void_p,
ctypes.c_void_p, ctypes.c_void_p]
ctypes.c_void_p,
ctypes.c_void_p]
self.EVP_CIPHER_CTX_new = self._lib.EVP_CIPHER_CTX_new
self.EVP_CIPHER_CTX_new.restype = ctypes.c_void_p
@ -223,13 +243,13 @@ class _OpenSSL:
self.EVP_aes_256_cbc.restype = ctypes.c_void_p
self.EVP_aes_256_cbc.argtypes = []
#self.EVP_aes_128_ctr = self._lib.EVP_aes_128_ctr
#self.EVP_aes_128_ctr.restype = ctypes.c_void_p
#self.EVP_aes_128_ctr.argtypes = []
# self.EVP_aes_128_ctr = self._lib.EVP_aes_128_ctr
# self.EVP_aes_128_ctr.restype = ctypes.c_void_p
# self.EVP_aes_128_ctr.argtypes = []
#self.EVP_aes_256_ctr = self._lib.EVP_aes_256_ctr
#self.EVP_aes_256_ctr.restype = ctypes.c_void_p
#self.EVP_aes_256_ctr.argtypes = []
# self.EVP_aes_256_ctr = self._lib.EVP_aes_256_ctr
# self.EVP_aes_256_ctr.restype = ctypes.c_void_p
# self.EVP_aes_256_ctr.argtypes = []
self.EVP_aes_128_ofb = self._lib.EVP_aes_128_ofb
self.EVP_aes_128_ofb.restype = ctypes.c_void_p
@ -377,6 +397,124 @@ class _OpenSSL:
ctypes.c_int, ctypes.c_void_p,
ctypes.c_int, ctypes.c_void_p]
# Blind signature requirements
self.BN_CTX_new = self._lib.BN_CTX_new
self.BN_CTX_new.restype = ctypes.c_void_p
self.BN_CTX_new.argtypes = []
self.BN_dup = self._lib.BN_dup
self.BN_dup.restype = ctypes.c_void_p
self.BN_dup.argtypes = [ctypes.c_void_p]
self.BN_rand = self._lib.BN_rand
self.BN_rand.restype = ctypes.c_int
self.BN_rand.argtypes = [ctypes.c_void_p,
ctypes.c_int,
ctypes.c_int]
self.BN_set_word = self._lib.BN_set_word
self.BN_set_word.restype = ctypes.c_int
self.BN_set_word.argtypes = [ctypes.c_void_p,
ctypes.c_ulong]
self.BN_mul = self._lib.BN_mul
self.BN_mul.restype = ctypes.c_int
self.BN_mul.argtypes = [ctypes.c_void_p,
ctypes.c_void_p,
ctypes.c_void_p,
ctypes.c_void_p]
self.BN_mod_add = self._lib.BN_mod_add
self.BN_mod_add.restype = ctypes.c_int
self.BN_mod_add.argtypes = [ctypes.c_void_p,
ctypes.c_void_p,
ctypes.c_void_p,
ctypes.c_void_p,
ctypes.c_void_p]
self.BN_mod_inverse = self._lib.BN_mod_inverse
self.BN_mod_inverse.restype = ctypes.c_void_p
self.BN_mod_inverse.argtypes = [ctypes.c_void_p,
ctypes.c_void_p,
ctypes.c_void_p,
ctypes.c_void_p]
self.BN_mod_mul = self._lib.BN_mod_mul
self.BN_mod_mul.restype = ctypes.c_int
self.BN_mod_mul.argtypes = [ctypes.c_void_p,
ctypes.c_void_p,
ctypes.c_void_p,
ctypes.c_void_p,
ctypes.c_void_p]
self.BN_lshift = self._lib.BN_lshift
self.BN_lshift.restype = ctypes.c_int
self.BN_lshift.argtypes = [ctypes.c_void_p,
ctypes.c_void_p,
ctypes.c_int]
self.BN_sub_word = self._lib.BN_sub_word
self.BN_sub_word.restype = ctypes.c_int
self.BN_sub_word.argtypes = [ctypes.c_void_p,
ctypes.c_ulong]
self.BN_cmp = self._lib.BN_cmp
self.BN_cmp.restype = ctypes.c_int
self.BN_cmp.argtypes = [ctypes.c_void_p,
ctypes.c_void_p]
self.BN_bn2dec = self._lib.BN_bn2dec
self.BN_bn2dec.restype = ctypes.c_char_p
self.BN_bn2dec.argtypes = [ctypes.c_void_p]
self.BN_CTX_free = self._lib.BN_CTX_free
self.BN_CTX_free.argtypes = [ctypes.c_void_p]
self.EC_GROUP_new_by_curve_name = self._lib.EC_GROUP_new_by_curve_name
self.EC_GROUP_new_by_curve_name.restype = ctypes.c_void_p
self.EC_GROUP_new_by_curve_name.argtypes = [ctypes.c_int]
self.EC_GROUP_get_order = self._lib.EC_GROUP_get_order
self.EC_GROUP_get_order.restype = ctypes.c_int
self.EC_GROUP_get_order.argtypes = [ctypes.c_void_p,
ctypes.c_void_p,
ctypes.c_void_p]
self.EC_GROUP_get_cofactor = self._lib.EC_GROUP_get_cofactor
self.EC_GROUP_get_cofactor.restype = ctypes.c_int
self.EC_GROUP_get_cofactor.argtypes = [ctypes.c_void_p,
ctypes.c_void_p,
ctypes.c_void_p]
self.EC_GROUP_get0_generator = self._lib.EC_GROUP_get0_generator
self.EC_GROUP_get0_generator.restype = ctypes.c_void_p
self.EC_GROUP_get0_generator.argtypes = [ctypes.c_void_p]
self.EC_POINT_copy = self._lib.EC_POINT_copy
self.EC_POINT_copy.restype = ctypes.c_int
self.EC_POINT_copy.argtypes = [ctypes.c_void_p,
ctypes.c_void_p]
self.EC_POINT_add = self._lib.EC_POINT_add
self.EC_POINT_add.restype = ctypes.c_int
self.EC_POINT_add.argtypes = [ctypes.c_void_p,
ctypes.c_void_p,
ctypes.c_void_p,
ctypes.c_void_p,
ctypes.c_void_p]
self.EC_POINT_cmp = self._lib.EC_POINT_cmp
self.EC_POINT_cmp.restype = ctypes.c_int
self.EC_POINT_cmp.argtypes = [ctypes.c_void_p,
ctypes.c_void_p,
ctypes.c_void_p,
ctypes.c_void_p]
self.EC_POINT_set_to_infinity = self._lib.EC_POINT_set_to_infinity
self.EC_POINT_set_to_infinity.restype = ctypes.c_int
self.EC_POINT_set_to_infinity.argtypes = [ctypes.c_void_p,
ctypes.c_void_p]
self._set_ciphers()
self._set_curves()
@ -388,11 +526,11 @@ class _OpenSSL:
'aes-256-cfb': CipherName('aes-256-cfb', self.EVP_aes_256_cfb128, 16),
'aes-128-ofb': CipherName('aes-128-ofb', self._lib.EVP_aes_128_ofb, 16),
'aes-256-ofb': CipherName('aes-256-ofb', self._lib.EVP_aes_256_ofb, 16),
#'aes-128-ctr': CipherName('aes-128-ctr', self._lib.EVP_aes_128_ctr, 16),
#'aes-256-ctr': CipherName('aes-256-ctr', self._lib.EVP_aes_256_ctr, 16),
# 'aes-128-ctr': CipherName('aes-128-ctr', self._lib.EVP_aes_128_ctr, 16),
# 'aes-256-ctr': CipherName('aes-256-ctr', self._lib.EVP_aes_256_ctr, 16),
'bf-cfb': CipherName('bf-cfb', self.EVP_bf_cfb64, 8),
'bf-cbc': CipherName('bf-cbc', self.EVP_bf_cbc, 8),
'rc4': CipherName('rc4', self.EVP_rc4, 128), # 128 is the initialisation size not block size
'rc4': CipherName('rc4', self.EVP_rc4, 128), # 128 is the initialisation size not block size
}
def _set_curves(self):
@ -494,22 +632,23 @@ class _OpenSSL:
buffer = self.create_string_buffer(size)
return buffer
def loadOpenSSL():
global OpenSSL
from os import path, environ
from ctypes.util import find_library
libdir = []
if getattr(sys,'frozen', None):
if getattr(sys, 'frozen', None):
if 'darwin' in sys.platform:
libdir.extend([
path.join(environ['RESOURCEPATH'], '..', 'Frameworks','libcrypto.dylib'),
path.join(environ['RESOURCEPATH'], '..', 'Frameworks','libcrypto.1.1.0.dylib'),
path.join(environ['RESOURCEPATH'], '..', 'Frameworks','libcrypto.1.0.2.dylib'),
path.join(environ['RESOURCEPATH'], '..', 'Frameworks','libcrypto.1.0.1.dylib'),
path.join(environ['RESOURCEPATH'], '..', 'Frameworks','libcrypto.1.0.0.dylib'),
path.join(environ['RESOURCEPATH'], '..', 'Frameworks','libcrypto.0.9.8.dylib'),
])
path.join(environ['RESOURCEPATH'], '..', 'Frameworks', 'libcrypto.dylib'),
path.join(environ['RESOURCEPATH'], '..', 'Frameworks', 'libcrypto.1.1.0.dylib'),
path.join(environ['RESOURCEPATH'], '..', 'Frameworks', 'libcrypto.1.0.2.dylib'),
path.join(environ['RESOURCEPATH'], '..', 'Frameworks', 'libcrypto.1.0.1.dylib'),
path.join(environ['RESOURCEPATH'], '..', 'Frameworks', 'libcrypto.1.0.0.dylib'),
path.join(environ['RESOURCEPATH'], '..', 'Frameworks', 'libcrypto.0.9.8.dylib'),
])
elif 'win32' in sys.platform or 'win64' in sys.platform:
libdir.append(path.join(sys._MEIPASS, 'libeay32.dll'))
else:
@ -548,4 +687,5 @@ def loadOpenSSL():
pass
raise Exception("Couldn't find and load the OpenSSL library. You must install it.")
loadOpenSSL()

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@ -0,0 +1,22 @@
"""
Test for ECC blind signatures
"""
import os
import unittest
from src.pyelliptic.eccblind import ECCBlind
class TestBlindSig(unittest.TestCase):
"""
Test case for ECC blind signature
"""
def test_blind_sig(self):
"""Test full sequence using a random certifier key and a random message"""
blind_sig = ECCBlind()
blind_sig.signer_init()
msg = os.urandom(64)
blind_sig.create_signing_request(msg)
blind_sig.blind_sign()
blind_sig.unblind()
self.assertTrue(blind_sig.verify())