85 lines
3.1 KiB
Python
85 lines
3.1 KiB
Python
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# Eos - Verifiable elections
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# Copyright © 2017 RunasSudo (Yingtong Li)
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#
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# This program is free software: you can redistribute it and/or modify
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# it under the terms of the GNU Affero General Public License as published by
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# the Free Software Foundation, either version 3 of the License, or
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# (at your option) any later version.
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#
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# This program is distributed in the hope that it will be useful,
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# but WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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# GNU Affero General Public License for more details.
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#
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# You should have received a copy of the GNU Affero General Public License
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# along with this program. If not, see <http://www.gnu.org/licenses/>.
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from eos.core.bigint import *
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from eos.core.objects import *
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class CyclicGroup(EmbeddedObject):
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p = EmbeddedObjectField(BigInt)
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g = EmbeddedObjectField(BigInt)
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@property
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def q(self):
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# p = 2q + 1
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return (self.p - ONE) // TWO
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def random_element(self, crypto_random=True):
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crypto_method = BigInt.crypto_random if crypto_random else BigInt.noncrypto_random
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return crypto_method(ONE, self.p - ONE)
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# RFC 3526
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DEFAULT_GROUP = CyclicGroup(
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p=BigInt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g=TWO
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)
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class EGPublicKey(EmbeddedObject):
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group = EmbeddedObjectField(CyclicGroup)
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X = EmbeddedObjectField(BigInt)
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# HAC 8.18
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def encrypt(self, message):
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# Choose an element 1 <= k <= p - 2
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k = BigInt.crypto_random(ONE, self.group.p - TWO)
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gamma = pow(self.group.g, k, self.group.p)
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delta = (message * pow(self.X, k, self.group.p)) % self.group.p
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return EGCiphertext(public_key=self, gamma=gamma, delta=delta)
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class EGPrivateKey(EmbeddedObject):
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public_key = EmbeddedObjectField(EGPublicKey)
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x = EmbeddedObjectField(BigInt)
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# HAC 8.17
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@staticmethod
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def generate():
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# Choose an element 1 <= x <= p - 2
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x = BigInt.crypto_random(ONE, DEFAULT_GROUP.p - TWO)
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# Calculate the public key as G^x
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X = pow(DEFAULT_GROUP.g, x, DEFAULT_GROUP.p)
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pk = EGPublicKey(group=DEFAULT_GROUP, X=X)
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sk = EGPrivateKey(public_key=pk, x=x)
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return sk
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# HAC 8.18
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def decrypt(self, ciphertext):
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if (
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ciphertext.gamma <= ZERO or ciphertext.gamma >= self.public_key.group.p or
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ciphertext.delta <= ZERO or ciphertext.delta >= self.public_key.group.p
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):
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raise Exception('Ciphertext is malformed')
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gamma_inv = pow(ciphertext.gamma, self.public_key.group.p - ONE - self.x, self.public_key.group.p)
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return (gamma_inv * ciphertext.delta) % self.public_key.group.p
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class EGCiphertext(EmbeddedObject):
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public_key = EmbeddedObjectField(EGPublicKey)
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gamma = EmbeddedObjectField(BigInt) # G^k
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delta = EmbeddedObjectField(BigInt) # M X^k
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