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Code Issues Releases Wiki Activity

introduce uncompress_coords

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This commit is contained in:
Pavol Rusnak 2014-02-04 18:55:17 +01:00
parent 81f462a5c5
commit 8aaebe761b
2 changed files with 16 additions and 12 deletions
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27
ecdsa.c
View File

@ -388,6 +388,20 @@ int ecdsa_address_decode(const char *addr, uint8_t *out)
return 1;
}
void uncompress_coords(uint8_t odd, const bignum256 *x, bignum256 *y)
{
// y^2 = x^3 + 0*x + 7
memcpy(y, x, sizeof(bignum256)); // y is x
bn_multiply(x, y, &prime256k1); // y is x^2
bn_multiply(x, y, &prime256k1); // y is x^3
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);
}
}
int ecdsa_read_pubkey(const uint8_t *pub_key, curve_point *pub)
{
if (pub_key[0] == 0x04) {
@ -395,22 +409,11 @@ int ecdsa_read_pubkey(const uint8_t *pub_key, curve_point *pub)
bn_read_be(pub_key + 33, &(pub->y));
return 1;
}
if (pub_key[0] == 0x02 || pub_key[0] == 0x03) { // compute missing y coords
// y^2 = x^3 + 0*x + 7
bn_read_be(pub_key + 1, &(pub->x));
bn_read_be(pub_key + 1, &(pub->y)); // y is x
bn_multiply(&(pub->x), &(pub->y), &prime256k1); // y is x^2
bn_multiply(&(pub->x), &(pub->y), &prime256k1); // y is x^3
bn_addmodi(&(pub->y), 7, &prime256k1); // y is x^3 + 7
bn_sqrt(&(pub->y), &prime256k1); // y = sqrt(y)
if ((pub_key[0] & 0x01) != (pub->y.val[0] & 1)) {
bn_substract(&prime256k1, &(pub->y), &(pub->y)); // y = -y
bn_mod(&(pub->y), &prime256k1);
}
uncompress_coords(pub_key[0], &(pub->x), &(pub->y));
return 1;
}
// error
return 0;
}

1
ecdsa.h
View File

@ -35,6 +35,7 @@
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 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);
int ecdsa_sign_double(const uint8_t *priv_key, const uint8_t *msg, uint32_t msg_len, uint8_t *sig);