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Improve modular multiplication performance

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This commit is contained in:
Matthias Schiffer 2012-03-15 07:24:00 +01:00
parent eec9db5e4d
commit 20529b77df
1 changed files with 11 additions and 15 deletions
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26
src/ec25519_secret.c
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@ -25,8 +25,8 @@
*/
/*
Simple finite field operations on the prime field F_p for
p = 2^252 + 27742317777372353535851937790883648493, which
Simple finite field operations on the prime field F_q for
q = 2^252 + 27742317777372353535851937790883648493, which
is the order of the base point used for ec25519
*/
@ -152,35 +152,31 @@ void ecc_25519_secret_reduce(ecc_secret_key_256 *out, const ecc_secret_key_256 *
/* Montgomery modular multiplication algorithm */
static void montgomery(unsigned char out[32], const unsigned char a[32], const unsigned char b[32]) {
unsigned int a_i;
unsigned int i, j;
unsigned int r0;
unsigned int nq;
unsigned int u;
for (i = 0; i < 32; i++)
out[i] = 0;
for (i = 0; i < 256; i++) {
a_i = a[i / 8] >> (i & 7);
a_i &= 1;
u = out[0] + a_i*b[0];
r0 = u & 1;
u += r0 * q[0];
for (i = 0; i < 32; i++) {
u = out[0] + a[i]*b[0];
nq = (u*27) & 255;
u += nq*q[0];
for (j = 1; j < 32; ++j) {
u += (out[j] + a_i*b[j] + r0*q[j]) << 8;
out[j-1] = (u >> 1) & 255;
u += (out[j] + a[i]*b[j] + nq*q[j]) << 8;
u >>= 8;
out[j-1] = u;
}
out[31] = u >> 1;
out[31] = u >> 8;
}
}
void ecc_25519_secret_mult(ecc_secret_key_256 *out, const ecc_secret_key_256 *in1, const ecc_secret_key_256 *in2) {
/* 2^512 mod p */
/* 2^512 mod q */
static const unsigned char C[32] = {
0x01, 0x0f, 0x9c, 0x44, 0xe3, 0x11, 0x06, 0xa4,
0x47, 0x93, 0x85, 0x68, 0xa7, 0x1b, 0x0e, 0xd0,