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Code Issues Releases Wiki Activity

introduce point_multiply

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This commit is contained in:
Pavol Rusnak 2014-02-05 23:38:37 +01:00
parent fc144587e6
commit 6a856479a8
2 changed files with 31 additions and 4 deletions
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32
ecdsa.c
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@ -92,8 +92,35 @@ void point_double(curve_point *cp)
memcpy(&(cp->y), &yr, sizeof(bignum256));
}
// res = k * p
void point_multiply(const bignum256 *k, const curve_point *p, curve_point *res)
{
int i, j;
// result is zero
int is_zero = 1;
curve_point curr;
// initial res
memcpy(&curr, p, sizeof(curve_point));
for (i = 0; i < 9; i++) {
for (j = 0; j < 30; j++) {
if (i == 8 && (k->val[i] >> j) == 0) break;
if (k->val[i] & (1u << j)) {
if (is_zero) {
memcpy(res, &curr, sizeof(curve_point));
is_zero = 0;
} else {
point_add(&curr, res);
}
}
point_double(&curr);
}
}
bn_mod(&(res->x), &prime256k1);
bn_mod(&(res->y), &prime256k1);
}
// res = k * G
void scalar_multiply(bignum256 *k, curve_point *res)
void scalar_multiply(const bignum256 *k, curve_point *res)
{
int i, j;
// result is zero
@ -397,8 +424,7 @@ void uncompress_coords(uint8_t odd, const bignum256 *x, bignum256 *y)
bn_addmodi(y, 7, &prime256k1); // y is x^3 + 7
bn_sqrt(y, &prime256k1); // y = sqrt(y)
if ((odd & 0x01) != (y->val[0] & 1)) {
bn_substract(&prime256k1, y, y); // y = -y
bn_mod(y, &prime256k1);
bn_substract_noprime(&prime256k1, y, y); // y = -y
}
}

3
ecdsa.h
View File

@ -34,7 +34,8 @@
void point_add(const curve_point *cp1, curve_point *cp2);
void point_double(curve_point *cp);
void scalar_multiply(bignum256 *k, curve_point *res);
void point_multiply(const bignum256 *k, const curve_point *p, curve_point *res);
void scalar_multiply(const bignum256 *k, curve_point *res);
void uncompress_coords(uint8_t odd, const bignum256 *x, bignum256 *y);
int ecdsa_sign(const uint8_t *priv_key, const uint8_t *msg, uint32_t msg_len, uint8_t *sig);