55 lines
1.9 KiB
C
55 lines
1.9 KiB
C
/**********************************************************************
|
|
* Copyright (c) 2015 Andrew Poelstra *
|
|
* Distributed under the MIT software license, see the accompanying *
|
|
* file COPYING or http://www.opensource.org/licenses/mit-license.php.*
|
|
**********************************************************************/
|
|
|
|
#ifndef SECP256K1_MODULE_ECDH_MAIN_H
|
|
#define SECP256K1_MODULE_ECDH_MAIN_H
|
|
|
|
#include "include/secp256k1_ecdh.h"
|
|
#include "ecmult_const_impl.h"
|
|
|
|
int secp256k1_ecdh(const secp256k1_context* ctx, unsigned char *result, const secp256k1_pubkey *point, const unsigned char *scalar) {
|
|
int ret = 0;
|
|
int overflow = 0;
|
|
secp256k1_gej res;
|
|
secp256k1_ge pt;
|
|
secp256k1_scalar s;
|
|
VERIFY_CHECK(ctx != NULL);
|
|
ARG_CHECK(result != NULL);
|
|
ARG_CHECK(point != NULL);
|
|
ARG_CHECK(scalar != NULL);
|
|
|
|
secp256k1_pubkey_load(ctx, &pt, point);
|
|
secp256k1_scalar_set_b32(&s, scalar, &overflow);
|
|
if (overflow || secp256k1_scalar_is_zero(&s)) {
|
|
ret = 0;
|
|
} else {
|
|
unsigned char x[32];
|
|
unsigned char y[1];
|
|
secp256k1_sha256 sha;
|
|
|
|
secp256k1_ecmult_const(&res, &pt, &s, 256);
|
|
secp256k1_ge_set_gej(&pt, &res);
|
|
/* Compute a hash of the point in compressed form
|
|
* Note we cannot use secp256k1_eckey_pubkey_serialize here since it does not
|
|
* expect its output to be secret and has a timing sidechannel. */
|
|
secp256k1_fe_normalize(&pt.x);
|
|
secp256k1_fe_normalize(&pt.y);
|
|
secp256k1_fe_get_b32(x, &pt.x);
|
|
y[0] = 0x02 | secp256k1_fe_is_odd(&pt.y);
|
|
|
|
secp256k1_sha256_initialize(&sha);
|
|
secp256k1_sha256_write(&sha, y, sizeof(y));
|
|
secp256k1_sha256_write(&sha, x, sizeof(x));
|
|
secp256k1_sha256_finalize(&sha, result);
|
|
ret = 1;
|
|
}
|
|
|
|
secp256k1_scalar_clear(&s);
|
|
return ret;
|
|
}
|
|
|
|
#endif /* SECP256K1_MODULE_ECDH_MAIN_H */
|