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reduce parameter of elgamal

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pull/2/head
MITSUNARI Shigeo 6 years ago
parent f33ef2ee85
commit 8cbdc129f6
1 changed files with 38 additions and 48 deletions
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  1. 86
      include/mcl/elgamal.hpp

86
include/mcl/elgamal.hpp
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@ -179,7 +179,6 @@ struct ElgamalT {
class PublicKey {
size_t bitSize;
Ec f;
Ec g;
Ec h;
bool enableWindowMethod_;
@ -196,8 +195,6 @@ struct ElgamalT {
}
}
template<class N>
void mulF(Ec& z, const N& n) const { mulDispatch(z, f, n, wm_f); }
template<class N>
void mulG(Ec& z, const N& n) const { mulDispatch(z, g, n, wm_g); }
template<class N>
void mulH(Ec& z, const N& n) const { mulDispatch(z, h, n, wm_h); }
@ -209,16 +206,14 @@ struct ElgamalT {
}
void enableWindowMethod(size_t winSize = 10)
{
wm_f.init(f, bitSize, winSize);
wm_g.init(g, bitSize, winSize);
wm_h.init(h, bitSize, winSize);
enableWindowMethod_ = true;
}
const Ec& getF() const { return f; }
void init(size_t bitSize, const Ec& f, const Ec& g, const Ec& h)
const Ec& getG() const { return g; }
void init(size_t bitSize, const Ec& g, const Ec& h)
{
this->bitSize = bitSize;
this->f = f;
this->g = g;
this->h = h;
enableWindowMethod_ = false;
@ -227,7 +222,7 @@ struct ElgamalT {
/*
encode message
input : m
output : c = (c1, c2) = (g^u, h^u f^m)
output : c = (c1, c2) = (g^u, h^u g^m)
*/
void enc(CipherText& c, const Zn& m, fp::RandGen rg = fp::RandGen()) const
{
@ -236,7 +231,7 @@ struct ElgamalT {
mulG(c.c1, u);
mulH(c.c2, u);
Ec t;
mulF(t, m);
mulG(t, m);
Ec::add(c.c2, c.c2, t);
}
/*
@ -254,7 +249,7 @@ struct ElgamalT {
mulG(c.c1, u);
mulH(c.c2, u);
if (m) {
Ec::add(c.c2, c.c2, f);
Ec::add(c.c2, c.c2, g);
Zn r1;
r1.setRand(rg);
zkp.c0.setRand(rg);
@ -270,7 +265,7 @@ struct ElgamalT {
mulG(R11, r1);
mulH(R12, r1);
std::ostringstream os;
os << R01 << R02 << R11 << R12 << c.c1 << c.c2 << f << g << h;
os << R01 << R02 << R11 << R12 << c.c1 << c.c2 << g << h;
Zn cc;
cc.setHashOf(os.str());
zkp.c1 = cc - zkp.c0;
@ -288,11 +283,11 @@ struct ElgamalT {
Ec::mul(t2, c.c1, zkp.c1);
Ec::sub(R11, t1, t2);
mulH(t1, zkp.s1);
Ec::sub(t2, c.c2, f);
Ec::sub(t2, c.c2, g);
Ec::mul(t2, t2, zkp.c1);
Ec::sub(R12, t1, t2);
std::ostringstream os;
os << R01 << R02 << R11 << R12 << c.c1 << c.c2 << f << g << h;
os << R01 << R02 << R11 << R12 << c.c1 << c.c2 << g << h;
Zn cc;
cc.setHashOf(os.str());
zkp.c0 = cc - zkp.c1;
@ -316,11 +311,11 @@ struct ElgamalT {
Ec::mul(t2, c.c1, zkp.c1);
Ec::sub(R11, t1, t2);
mulH(t1, zkp.s1);
Ec::sub(t2, c.c2, f);
Ec::sub(t2, c.c2, g);
Ec::mul(t2, t2, zkp.c1);
Ec::sub(R12, t1, t2);
std::ostringstream os;
os << R01 << R02 << R11 << R12 << c.c1 << c.c2 << f << g << h;
os << R01 << R02 << R11 << R12 << c.c1 << c.c2 << g << h;
Zn cc;
cc.setHashOf(os.str());
return cc == zkp.c0 + zkp.c1;
@ -343,13 +338,13 @@ struct ElgamalT {
/*
add encoded message with plain message
input : c = Enc(m1) = (c1, c2), m2
ouput : c = Enc(m1 + m2) = (c1, c2 f^m2)
ouput : c = Enc(m1 + m2) = (c1, c2 g^m2)
*/
template<class N>
void add(CipherText& c, const N& m) const
{
Ec fm;
mulF(fm, m);
mulG(fm, m);
Ec::add(c.c2, c.c2, fm);
}
template<class InputStream>
@ -358,10 +353,9 @@ struct ElgamalT {
std::string s;
mcl::fp::local::loadWord(s, is);
bitSize = cybozu::atoi(s);
f.load(is, ioMode);
g.load(is, ioMode);
h.load(is, ioMode);
init(bitSize, f, g, h);
init(bitSize, g, h);
}
template<class OutputStream>
void save(OutputStream& os, int ioMode = IoSerialize) const
@ -371,7 +365,6 @@ struct ElgamalT {
cybozu::writeChar(os, ' ');
const char sep = *fp::getIoSeparator(ioMode);
f.save(os, ioMode);
if (sep) cybozu::writeChar(os, sep);
g.save(os, ioMode);
if (sep) cybozu::writeChar(os, sep);
@ -410,7 +403,7 @@ struct ElgamalT {
void fromStr(const std::string& str) { setStr(str); }
};
/*
create table f^i for i in [rangeMin, rangeMax]
create table g^i for i in [rangeMin, rangeMax]
*/
struct PowerCache {
#if (CYBOZU_CPP_VERSION > CYBOZU_CPP_VERSION_CP03)
@ -419,18 +412,18 @@ struct ElgamalT {
typedef std::map<Ec, int> Cache;
#endif
Cache cache;
void init(const Ec& f, int rangeMin, int rangeMax)
void init(const Ec& g, int rangeMin, int rangeMax)
{
if (rangeMin > rangeMax) throw cybozu::Exception("mcl:ElgamalT:PowerCache:bad range") << rangeMin << rangeMax;
Ec x;
x.clear();
cache[x] = 0;
for (int i = 1; i <= rangeMax; i++) {
Ec::add(x, x, f);
Ec::add(x, x, g);
cache[x] = i;
}
Ec nf;
Ec::neg(nf, f);
Ec::neg(nf, g);
x.clear();
for (int i = -1; i >= rangeMin; i--) {
Ec::add(x, x, nf);
@ -438,17 +431,17 @@ struct ElgamalT {
}
}
/*
return m such that f^m = g
return m such that g^m = y
*/
int getExponent(const Ec& g, bool *b = 0) const
int getExponent(const Ec& y, bool *b = 0) const
{
typename Cache::const_iterator i = cache.find(g);
typename Cache::const_iterator i = cache.find(y);
if (i == cache.end()) {
if (b) {
*b = false;
return 0;
}
throw cybozu::Exception("Elgamal:PowerCache:getExponent:not found") << g;
throw cybozu::Exception("Elgamal:PowerCache:getExponent:not found") << y;
}
if (b) *b = true;
return i->second;
@ -469,20 +462,17 @@ struct ElgamalT {
public:
/*
init
input : f
output : (g, h, z)
Ec = <f>
g in Ec
input : g
output : (h, z)
Ec = <g>
h = g^z
*/
void init(const Ec& f, size_t bitSize, fp::RandGen rg = fp::RandGen())
void init(const Ec& g, size_t bitSize, fp::RandGen rg = fp::RandGen())
{
Ec g, h;
z.setRand(rg);
Ec::mul(g, f, z);
Ec h;
z.setRand(rg);
Ec::mul(h, g, z);
pub.init(bitSize, f, g, h);
pub.init(bitSize, g, h);
}
const PublicKey& getPublicKey() const { return pub; }
/*
@ -490,12 +480,12 @@ struct ElgamalT {
input : c = (c1, c2)
output : m
M = c2 / c1^z
find m such that M = f^m and |m| < limit
find m such that M = g^m and |m| < limit
@memo 7sec@core i3 for m = 1e6
*/
void dec(Zn& m, const CipherText& c, int limit = 100000) const
{
const Ec& f = pub.getF();
const Ec& g = pub.getG();
Ec c1z;
Ec::mul(c1z, c.c1, z);
if (c1z == c.c2) {
@ -505,12 +495,12 @@ struct ElgamalT {
Ec t1(c1z);
Ec t2(c.c2);
for (int i = 1; i < limit; i++) {
Ec::add(t1, t1, f);
Ec::add(t1, t1, g);
if (t1 == c.c2) {
m = i;
return;
}
Ec::add(t2, t2, f);
Ec::add(t2, t2, g);
if (t2 == c1z) {
m = -i;
return;
@ -519,20 +509,20 @@ struct ElgamalT {
throw cybozu::Exception("elgamal:PrivateKey:dec:overflow");
}
/*
powfm = c2 / c1^z = f^m
powgm = c2 / c1^z = g^m
*/
void getPowerf(Ec& powfm, const CipherText& c) const
void getPowerg(Ec& powgm, const CipherText& c) const
{
Ec c1z;
Ec::mul(c1z, c.c1, z);
Ec::sub(powfm, c.c2, c1z);
Ec::sub(powgm, c.c2, c1z);
}
/*
set range of message to decode quickly
*/
void setCache(int rangeMin, int rangeMax)
{
cache.init(pub.getF(), rangeMin, rangeMax);
cache.init(pub.getG(), rangeMin, rangeMax);
}
/*
clear cache
@ -550,9 +540,9 @@ struct ElgamalT {
*/
int dec(const CipherText& c, bool *b = 0) const
{
Ec powfm;
getPowerf(powfm, c);
return cache.getExponent(powfm, b);
Ec powgm;
getPowerg(powgm, c);
return cache.getExponent(powgm, b);
}
/*
check whether c is encrypted zero message

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