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594 lines
14 KiB
594 lines
14 KiB
#pragma once
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/**
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@file
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@brief lifted-ElGamal encryption
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@author MITSUNARI Shigeo(@herumi)
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@license modified new BSD license
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http://opensource.org/licenses/BSD-3-Clause
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original:
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Copyright (c) 2014, National Institute of Advanced Industrial
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Science and Technology All rights reserved.
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This source file is subject to BSD 3-Clause license.
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*/
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#include <string>
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#include <sstream>
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#include <cybozu/unordered_map.hpp>
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#ifndef CYBOZU_UNORDERED_MAP_STD
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#include <map>
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#endif
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#include <cybozu/exception.hpp>
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#include <cybozu/itoa.hpp>
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#include <cybozu/atoi.hpp>
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#include <mcl/window_method.hpp>
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namespace mcl {
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template<class _Ec, class Zn>
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struct ElgamalT {
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typedef _Ec Ec;
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struct CipherText {
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Ec c1;
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Ec c2;
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/*
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(c1, c2) = (0, 0) is trivial valid ciphertext for m = 0
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*/
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void clear()
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{
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c1.clear();
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c2.clear();
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}
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/*
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add encoded message with encoded message
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input : this = Enc(m1), c = Enc(m2)
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output : this = Enc(m1 + m2)
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*/
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void add(const CipherText& c)
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{
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Ec::add(c1, c1, c.c1);
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Ec::add(c2, c2, c.c2);
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}
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/*
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mul by x
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input : this = Enc(m), x
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output : this = Enc(m x)
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*/
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template<class N>
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void mul(const N& x)
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{
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Ec::mul(c1, c1, x);
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Ec::mul(c2, c2, x);
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}
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/*
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negative encoded message
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input : this = Enc(m)
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output : this = Enc(-m)
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*/
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void neg()
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{
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Ec::neg(c1, c1);
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Ec::neg(c2, c2);
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}
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std::istream& readStream(std::istream& is, int ioMode)
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{
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c1.readStream(is, ioMode);
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c2.readStream(is, ioMode);
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if (!is) throw cybozu::Exception("ElgamalT:CipherText:readStream");
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return is;
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}
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void getStr(std::string& str, int ioMode = 0) const
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{
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const char *sep = fp::getIoSeparator(ioMode);
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str = c1.getStr(ioMode);
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str += sep;
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str += c2.getStr(ioMode);
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}
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std::string getStr(int ioMode = 0) const
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{
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std::string str;
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getStr(str, ioMode);
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return str;
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}
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void setStr(const std::string& str, int ioMode = 0)
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{
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std::istringstream is(str);
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readStream(is, ioMode);
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}
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friend inline std::ostream& operator<<(std::ostream& os, const CipherText& self)
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{
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int ioMode = fp::detectIoMode(Ec::Fp::BaseFp::getIoMode(), os);
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return os << self.getStr(ioMode);
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}
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friend inline std::istream& operator>>(std::istream& is, CipherText& self)
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{
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int ioMode = fp::detectIoMode(Ec::Fp::BaseFp::getIoMode(), is);
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return self.readStream(is, ioMode);
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}
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// obsolete
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std::string toStr() const { return getStr(); }
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void fromStr(const std::string& str) { setStr(str); }
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};
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/*
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Zero Knowledge Proof
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cipher text with ZKP to ensure m = 0 or 1
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http://dx.doi.org/10.1587/transfun.E96.A.1156
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*/
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struct Zkp {
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Zn c0, c1, s0, s1;
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std::istream& readStream(std::istream& is, int ioMode)
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{
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c0.readStream(is, ioMode);
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c1.readStream(is, ioMode);
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s0.readStream(is, ioMode);
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s1.readStream(is, ioMode);
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if (!is) throw cybozu::Exception("ElgamalT:Zkp:readStream");
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return is;
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}
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void getStr(std::string& str, int ioMode = 0) const
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{
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const char *sep = fp::getIoSeparator(ioMode);
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str = c0.getStr(ioMode);
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str += sep;
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str += c1.getStr(ioMode);
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str += sep;
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str += s0.getStr(ioMode);
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str += sep;
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str += s1.getStr(ioMode);
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}
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std::string getStr(int ioMode = 0) const
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{
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std::string str;
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getStr(str, ioMode);
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return str;
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}
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void setStr(const std::string& str, int ioMode = 0)
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{
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std::istringstream is(str);
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readStream(is, ioMode);
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}
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friend inline std::ostream& operator<<(std::ostream& os, const Zkp& self)
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{
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int ioMode = fp::detectIoMode(Ec::Fp::BaseFp::getIoMode(), os);
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return os << self.getStr(ioMode);
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}
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friend inline std::istream& operator>>(std::istream& is, Zkp& self)
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{
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int ioMode = fp::detectIoMode(Ec::Fp::BaseFp::getIoMode(), is);
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return self.readStream(is, ioMode);
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}
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// obsolete
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std::string toStr() const { return getStr(); }
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void fromStr(const std::string& str) { setStr(str); }
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};
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class PublicKey {
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size_t bitSize;
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Ec f;
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Ec g;
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Ec h;
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bool enableWindowMethod_;
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fp::WindowMethod<Ec> wm_f;
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fp::WindowMethod<Ec> wm_g;
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fp::WindowMethod<Ec> wm_h;
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template<class N>
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void mulDispatch(Ec& z, const Ec& x, const N& n, const fp::WindowMethod<Ec>& pw) const
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{
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if (enableWindowMethod_) {
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pw.mul(z, n);
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} else {
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Ec::mul(z, x, n);
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}
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}
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template<class N>
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void mulF(Ec& z, const N& n) const { mulDispatch(z, f, n, wm_f); }
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template<class N>
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void mulG(Ec& z, const N& n) const { mulDispatch(z, g, n, wm_g); }
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template<class N>
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void mulH(Ec& z, const N& n) const { mulDispatch(z, h, n, wm_h); }
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public:
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PublicKey()
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: bitSize(0)
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, enableWindowMethod_(false)
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{
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}
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void enableWindowMethod(size_t winSize = 10)
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{
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wm_f.init(f, bitSize, winSize);
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wm_g.init(g, bitSize, winSize);
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wm_h.init(h, bitSize, winSize);
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enableWindowMethod_ = true;
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}
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const Ec& getF() const { return f; }
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void init(size_t bitSize, const Ec& f, const Ec& g, const Ec& h)
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{
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this->bitSize = bitSize;
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this->f = f;
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this->g = g;
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this->h = h;
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enableWindowMethod_ = false;
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}
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/*
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encode message
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input : m
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output : c = (c1, c2) = (g^u, h^u f^m)
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*/
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template<class RG>
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void enc(CipherText& c, const Zn& m, RG& rg) const
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{
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Zn u;
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u.setRand(rg);
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mulG(c.c1, u);
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mulH(c.c2, u);
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Ec t;
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mulF(t, m);
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Ec::add(c.c2, c.c2, t);
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}
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/*
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encode message
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input : m = 0 or 1
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output : c (c1, c2), zkp
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*/
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template<class RG, class Hash>
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void encWithZkp(CipherText& c, Zkp& zkp, int m, Hash& hash, RG& rg) const
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{
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if (m != 0 && m != 1) {
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throw cybozu::Exception("elgamal:PublicKey:encWithZkp") << m;
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}
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Zn u;
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u.setRand(rg);
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mulG(c.c1, u);
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mulH(c.c2, u);
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if (m) {
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Ec::add(c.c2, c.c2, f);
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Zn r1;
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r1.setRand(rg);
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zkp.c0.setRand(rg);
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zkp.s0.setRand(rg);
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Ec R01, R02, R11, R12;
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Ec t1, t2;
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mulG(t1, zkp.s0);
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Ec::mul(t2, c.c1, zkp.c0);
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Ec::sub(R01, t1, t2);
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mulH(t1, zkp.s0);
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Ec::mul(t2, c.c2, zkp.c0);
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Ec::sub(R02, t1, t2);
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mulG(R11, r1);
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mulH(R12, r1);
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std::ostringstream os;
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os << R01 << R02 << R11 << R12 << c.c1 << c.c2 << f << g << h;
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hash.update(os.str());
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const std::string digest = hash.digest();
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Zn cc;
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cc.setArrayMask(digest.c_str(), digest.size());
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zkp.c1 = cc - zkp.c0;
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zkp.s1 = r1 + zkp.c1 * u;
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} else {
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Zn r0;
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r0.setRand(rg);
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zkp.c1.setRand(rg);
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zkp.s1.setRand(rg);
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Ec R01, R02, R11, R12;
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mulG(R01, r0);
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mulH(R02, r0);
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Ec t1, t2;
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mulG(t1, zkp.s1);
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Ec::mul(t2, c.c1, zkp.c1);
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Ec::sub(R11, t1, t2);
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mulH(t1, zkp.s1);
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Ec::sub(t2, c.c2, f);
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Ec::mul(t2, t2, zkp.c1);
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Ec::sub(R12, t1, t2);
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std::ostringstream os;
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os << R01 << R02 << R11 << R12 << c.c1 << c.c2 << f << g << h;
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hash.update(os.str());
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const std::string digest = hash.digest();
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Zn c;
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c.setArrayMask(digest.c_str(), digest.size());
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zkp.c0 = c - zkp.c1;
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zkp.s0 = r0 + zkp.c0 * u;
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}
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}
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/*
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verify cipher text with ZKP
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*/
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template<class Hash>
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bool verify(const CipherText& c, const Zkp& zkp, Hash& hash) const
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{
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Ec R01, R02, R11, R12;
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Ec t1, t2;
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mulG(t1, zkp.s0);
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Ec::mul(t2, c.c1, zkp.c0);
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Ec::sub(R01, t1, t2);
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mulH(t1, zkp.s0);
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Ec::mul(t2, c.c2, zkp.c0);
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Ec::sub(R02, t1, t2);
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mulG(t1, zkp.s1);
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Ec::mul(t2, c.c1, zkp.c1);
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Ec::sub(R11, t1, t2);
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mulH(t1, zkp.s1);
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Ec::sub(t2, c.c2, f);
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Ec::mul(t2, t2, zkp.c1);
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Ec::sub(R12, t1, t2);
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std::ostringstream os;
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os << R01 << R02 << R11 << R12 << c.c1 << c.c2 << f << g << h;
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hash.update(os.str());
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const std::string digest = hash.digest();
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Zn cc;
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cc.setArrayMask(digest.c_str(), digest.size());
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return cc == zkp.c0 + zkp.c1;
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}
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/*
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rerandomize encoded message
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input : c = (c1, c2)
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output : c = (c1 g^v, c2 h^v)
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*/
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template<class RG>
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void rerandomize(CipherText& c, RG& rg) const
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{
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Zn v;
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v.setRand(rg);
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Ec t;
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mulG(t, v);
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Ec::add(c.c1, c.c1, t);
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mulH(t, v);
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Ec::add(c.c2, c.c2, t);
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}
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/*
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add encoded message with plain message
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input : c = Enc(m1) = (c1, c2), m2
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ouput : c = Enc(m1 + m2) = (c1, c2 f^m2)
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*/
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template<class N>
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void add(CipherText& c, const N& m) const
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{
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Ec fm;
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mulF(fm, m);
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Ec::add(c.c2, c.c2, fm);
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}
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std::istream& readStream(std::istream& is, int ioMode)
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{
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std::string s;
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is >> s;
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bitSize = cybozu::atoi(s);
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char c;
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is.read(&c, 1);
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if (c != ' ') throw cybozu::Exception("ElgamalT:PublicKey:readStream:bad separator") << int(c);
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f.readStream(is, ioMode);
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g.readStream(is, ioMode);
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h.readStream(is, ioMode);
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if (!is) throw cybozu::Exception("ElgamalT:PublicKey:readStream");
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init(bitSize, f, g, h);
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return is;
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}
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void getStr(std::string& str, int ioMode = 0) const
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{
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const char *sep = fp::getIoSeparator(ioMode);
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str = cybozu::itoa(bitSize);
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str += ' ';
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str += f.getStr(ioMode);
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str += sep;
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str += g.getStr(ioMode);
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str += sep;
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str += h.getStr(ioMode);
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}
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std::string getStr(int ioMode = 0) const
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{
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std::string str;
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getStr(str, ioMode);
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return str;
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}
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void setStr(const std::string& str, int ioMode = 0)
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{
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std::istringstream is(str);
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readStream(is, ioMode);
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}
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friend inline std::ostream& operator<<(std::ostream& os, const PublicKey& self)
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{
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int ioMode = fp::detectIoMode(Ec::Fp::BaseFp::getIoMode(), os);
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return os << self.getStr(ioMode);
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}
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friend inline std::istream& operator>>(std::istream& is, PublicKey& self)
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{
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int ioMode = fp::detectIoMode(Ec::Fp::BaseFp::getIoMode(), is);
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return self.readStream(is, ioMode);
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}
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// obsolete
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std::string toStr() const { return getStr(); }
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void fromStr(const std::string& str) { setStr(str); }
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};
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/*
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create table f^i for i in [rangeMin, rangeMax]
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*/
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struct PowerCache {
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#if (CYBOZU_CPP_VERSION > CYBOZU_CPP_VERSION_CP03)
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typedef CYBOZU_NAMESPACE_STD::unordered_map<Ec, int> Cache;
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#else
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typedef std::map<Ec, int> Cache;
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#endif
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Cache cache;
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void init(const Ec& f, int rangeMin, int rangeMax)
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{
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if (rangeMin > rangeMax) throw cybozu::Exception("mcl:ElgamalT:PowerCache:bad range") << rangeMin << rangeMax;
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Ec x;
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x.clear();
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cache[x] = 0;
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for (int i = 1; i <= rangeMax; i++) {
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Ec::add(x, x, f);
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cache[x] = i;
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}
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Ec nf;
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Ec::neg(nf, f);
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x.clear();
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for (int i = -1; i >= rangeMin; i--) {
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Ec::add(x, x, nf);
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cache[x] = i;
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}
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}
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/*
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return m such that f^m = g
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*/
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int getExponent(const Ec& g, bool *b = 0) const
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{
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typename Cache::const_iterator i = cache.find(g);
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if (i == cache.end()) {
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if (b) {
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*b = false;
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return 0;
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}
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throw cybozu::Exception("Elgamal:PowerCache:getExponent:not found") << g;
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}
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if (b) *b = true;
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return i->second;
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}
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void clear()
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{
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cache.clear();
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}
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bool isEmpty() const
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{
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return cache.empty();
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}
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};
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class PrivateKey {
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PublicKey pub;
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Zn z;
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PowerCache cache;
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public:
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/*
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init
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input : f
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output : (g, h, z)
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Ec = <f>
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g in Ec
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h = g^z
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*/
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template<class RG>
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void init(const Ec& f, size_t bitSize, RG& rg)
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{
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Ec g, h;
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z.setRand(rg);
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Ec::mul(g, f, z);
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z.setRand(rg);
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Ec::mul(h, g, z);
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pub.init(bitSize, f, g, h);
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}
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const PublicKey& getPublicKey() const { return pub; }
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/*
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decode message by brute-force attack
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input : c = (c1, c2)
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output : m
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M = c2 / c1^z
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find m such that M = f^m and |m| < limit
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@memo 7sec@core i3 for m = 1e6
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*/
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void dec(Zn& m, const CipherText& c, int limit = 100000) const
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{
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const Ec& f = pub.getF();
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Ec c1z;
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Ec::mul(c1z, c.c1, z);
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if (c1z == c.c2) {
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m = 0;
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return;
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}
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Ec t1(c1z);
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Ec t2(c.c2);
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for (int i = 1; i < limit; i++) {
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Ec::add(t1, t1, f);
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if (t1 == c.c2) {
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m = i;
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return;
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}
|
|
Ec::add(t2, t2, f);
|
|
if (t2 == c1z) {
|
|
m = -i;
|
|
return;
|
|
}
|
|
}
|
|
throw cybozu::Exception("elgamal:PrivateKey:dec:overflow");
|
|
}
|
|
/*
|
|
powfm = c2 / c1^z = f^m
|
|
*/
|
|
void getPowerf(Ec& powfm, const CipherText& c) const
|
|
{
|
|
Ec c1z;
|
|
Ec::mul(c1z, c.c1, z);
|
|
Ec::sub(powfm, c.c2, c1z);
|
|
}
|
|
/*
|
|
set range of message to decode quickly
|
|
*/
|
|
void setCache(int rangeMin, int rangeMax)
|
|
{
|
|
cache.init(pub.getF(), rangeMin, rangeMax);
|
|
}
|
|
/*
|
|
clear cache
|
|
*/
|
|
void clearCache()
|
|
{
|
|
cache.clear();
|
|
}
|
|
/*
|
|
decode message by lookup table if !cache.isEmpty()
|
|
brute-force attack otherwise
|
|
input : c = (c1, c2)
|
|
b : set false if not found
|
|
return m
|
|
*/
|
|
int dec(const CipherText& c, bool *b = 0) const
|
|
{
|
|
Ec powfm;
|
|
getPowerf(powfm, c);
|
|
return cache.getExponent(powfm, b);
|
|
}
|
|
/*
|
|
check whether c is encrypted zero message
|
|
*/
|
|
bool isZeroMessage(const CipherText& c) const
|
|
{
|
|
Ec c1z;
|
|
Ec::mul(c1z, c.c1, z);
|
|
return c.c2 == c1z;
|
|
}
|
|
std::istream& readStream(std::istream& is, int ioMode)
|
|
{
|
|
pub.readStream(is, ioMode);
|
|
z.readStream(is, ioMode);
|
|
if (!is) throw cybozu::Exception("ElgamalT:CipherText:readStream");
|
|
return is;
|
|
}
|
|
void getStr(std::string& str, int ioMode = 0) const
|
|
{
|
|
const char *sep = fp::getIoSeparator(ioMode);
|
|
str = pub.getStr(ioMode);
|
|
str += sep;
|
|
str += z.getStr(ioMode);
|
|
}
|
|
std::string getStr(int ioMode = 0) const
|
|
{
|
|
std::string str;
|
|
getStr(str, ioMode);
|
|
return str;
|
|
}
|
|
void setStr(const std::string& str, int ioMode = 0)
|
|
{
|
|
std::istringstream is(str);
|
|
readStream(is, ioMode);
|
|
}
|
|
friend inline std::ostream& operator<<(std::ostream& os, const PrivateKey& self)
|
|
{
|
|
int ioMode = fp::detectIoMode(Ec::Fp::BaseFp::getIoMode(), os);
|
|
return os << self.getStr(ioMode);
|
|
}
|
|
friend inline std::istream& operator>>(std::istream& is, PrivateKey& self)
|
|
{
|
|
int ioMode = fp::detectIoMode(Ec::Fp::BaseFp::getIoMode(), is);
|
|
return self.readStream(is, ioMode);
|
|
}
|
|
std::string toStr() const { return getStr(); }
|
|
void fromStr(const std::string& str) { setStr(str); }
|
|
};
|
|
};
|
|
|
|
} // mcl
|
|
|