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#pragma once
/**
@file
@brief paillier encryption
@author MITSUNARI Shigeo(@herumi)
@license modified new BSD license
http://opensource.org/licenses/BSD-3-Clause
*/
#include <mcl/gmp_util.hpp>
namespace mcl { namespace paillier {
class PublicKey {
size_t primeBitSize;
mpz_class g;
mpz_class n;
mpz_class n2;
public:
PublicKey() : primeBitSize(0) {}
void init(size_t _primeBitSize, const mpz_class& _n)
{
primeBitSize = _primeBitSize;
n = _n;
g = 1 + _n;
n2 = _n * _n;
}
void enc(mpz_class& c, const mpz_class& m, mcl::fp::RandGen rg = mcl::fp::RandGen()) const
{
if (rg.isZero()) rg = mcl::fp::RandGen::get();
if (primeBitSize == 0) throw cybozu::Exception("paillier:PublicKey:not init");
mpz_class r;
mcl::gmp::getRand(r, primeBitSize, rg);
mpz_class a, b;
mcl::gmp::powMod(a, g, m, n2);
mcl::gmp::powMod(b, r, n, n2);
c = (a * b) % n2;
}
/*
additive homomorphic encryption
cz = cx + cy
*/
void add(mpz_class& cz, mpz_class& cx, mpz_class& cy) const
{
cz = (cx * cy) % n2;
}
};
class SecretKey {
size_t primeBitSize;
mpz_class n;
mpz_class n2;
mpz_class lambda;
mpz_class invLambda;
public:
SecretKey() : primeBitSize(0) {}
/*
the size of prime is half of bitSize
*/
void init(size_t bitSize, mcl::fp::RandGen rg = mcl::fp::RandGen())
{
if (rg.isZero()) rg = mcl::fp::RandGen::get();
primeBitSize = bitSize / 2;
mpz_class p, q;
mcl::gmp::getRandPrime(p, primeBitSize, rg);
mcl::gmp::getRandPrime(q, primeBitSize, rg);
lambda = (p - 1) * (q - 1);
n = p * q;
n2 = n * n;
mcl::gmp::invMod(invLambda, lambda, n);
}
void getPublicKey(PublicKey& pub) const
{
pub.init(primeBitSize, n);
}
void dec(mpz_class& m, const mpz_class& c) const
{
mpz_class L;
mcl::gmp::powMod(L, c, lambda, n2);
L = ((L - 1) / n) % n;
m = (L * invLambda) % n;
}
};
} } // mcl::paillier
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