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square root + point decompression

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This commit is contained in:
Pieter Wuille
2013-03-05 02:32:47 +01:00
parent 2e4ca46072
commit af2348935e
1 changed files with 48 additions and 15 deletions
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63
secp256k1.cpp
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@ -249,6 +249,33 @@ public:
} }
void SetSquareRoot(const FieldElem &a) {
// calculate a^p, with p={12,15,24,30,31}
FieldElem a2; a2.SetSquare(a);
FieldElem a3; a3.SetMult(a2,a);
FieldElem a6; a6.SetSquare(a3);
FieldElem a12; a12.SetSquare(a6);
FieldElem a15; a15.SetMult(a12,a3);
FieldElem a24; a24.SetSquare(a12);
FieldElem a30; a30.SetSquare(a15);
FieldElem a31; a31.SetMult(a30,a);
FieldElem x = a15;
for (int i=0; i<43; i++) {
for (int j=0; j<5; j++) x.SetSquare(x);
x.SetMult(x,a31);
}
for (int j=0; j<5; j++) x.SetSquare(x);
x.SetMult(x,a30);
for (int i=0; i<4; i++) {
for (int j=0; j<5; j++) x.SetSquare(x);
x.SetMult(x,a31);
}
for (int j=0; j<5; j++) x.SetSquare(x);
x.SetMult(x,a24);
for (int j=0; j<5; j++) x.SetSquare(x);
SetMult(x,a12);
}
// computes the modular inverse, by computing a^(p-2) // computes the modular inverse, by computing a^(p-2)
// TODO: use extmod instead, much faster // TODO: use extmod instead, much faster
void SetInverse(const FieldElem &a) { void SetInverse(const FieldElem &a) {
@ -264,23 +291,18 @@ public:
FieldElem a31; a31.SetMult(a30,a); FieldElem a31; a31.SetMult(a30,a);
FieldElem x = a; FieldElem x = a;
for (int i=0; i<44; i++) { for (int i=0; i<44; i++) {
for (int j=0; j<5; j++) for (int j=0; j<5; j++) x.SetSquare(x);
x.SetSquare(x);
x.SetMult(x,a31); x.SetMult(x,a31);
} }
for (int j=0; j<5; j++) for (int j=0; j<5; j++) x.SetSquare(x);
x.SetSquare(x);
x.SetMult(x,a27); x.SetMult(x,a27);
for (int i=0; i<4; i++) { for (int i=0; i<4; i++) {
for (int j=0; j<5; j++) for (int j=0; j<5; j++) x.SetSquare(x);
x.SetSquare(x);
x.SetMult(x,a31); x.SetMult(x,a31);
} }
for (int j=0; j<5; j++) for (int j=0; j<5; j++) x.SetSquare(x);
x.SetSquare(x);
x.SetMult(x,a); x.SetMult(x,a);
for (int j=0; j<5; j++) for (int j=0; j<5; j++) x.SetSquare(x);
x.SetSquare(x);
SetMult(x,a13); SetMult(x,a13);
} }
@ -367,6 +389,17 @@ public:
yout = y; yout = y;
} }
bool SetCompressed(const F &xin) {
x = xin;
F x2; x2.SetSquare(x);
F x3; x3.SetMult(x,x2);
fInfinity = false;
F c(7);
c += x3;
y.SetSquareRoot(c);
z = F(1);
}
std::string ToString() { std::string ToString() {
F xt,yt; F xt,yt;
if (fInfinity) if (fInfinity)
@ -450,15 +483,15 @@ using namespace secp256k1;
int main() { int main() {
FieldElem f1,f2; FieldElem f1,f2;
f1.SetHex("8b30bbe9ae2a990696b22f670709dff3727fd8bc04d3362c6c7bf458e2846004"); f1.SetHex("8b30bbe9ae2a990696b22f670709dff3727fd8bc04d3362c6c7bf458e2846004");
f2.SetHex("a357ae915c4a65281309edf20504740f0eb3343990216b4f81063cb65f2f7e0f"); // f2.SetHex("a357ae915c4a65281309edf20504740f0eb3343990216b4f81063cb65f2f7e0f");
GroupElem<FieldElem> g1(f1,f2); GroupElem<FieldElem> g1; g1.SetCompressed(f1);
printf("%s\n", g1.ToString().c_str()); printf("%s\n", g1.ToString().c_str());
GroupElem<FieldElem> p = g1; GroupElem<FieldElem> p = g1;
GroupElem<FieldElem> q = p; GroupElem<FieldElem> q = p;
printf("ok %i\n", (int)p.IsValid()); printf("ok %i\n", (int)p.IsValid());
for (int i=0; i<100000000; i++) { for (int i=0; i<1000000; i++) {
p.SetAdd(p,g1); p.SetCompressed(f1);
q.SetAdd(q,p); f1.SetSquare(f1);
} }
printf("ok %i\n", (int)q.IsValid()); printf("ok %i\n", (int)q.IsValid());
printf("%s\n", q.ToString().c_str()); printf("%s\n", q.ToString().c_str());