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[ECDH API change] Support custom hash function

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This commit is contained in:
Kirill Fomichev
2015-11-12 11:43:06 +03:00
parent 452d8e4d2a
commit b00be65056
5 changed files with 93 additions and 35 deletions
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38
src/modules/ecdh/main_impl.h
View File

@@ -10,16 +10,34 @@
#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) {
static int ecdh_hash_function_sha256(unsigned char *output, const unsigned char *x, const unsigned char *y) {
unsigned char version = (y[31] & 0x01) | 0x02;
secp256k1_sha256 sha;
secp256k1_sha256_initialize(&sha);
secp256k1_sha256_write(&sha, &version, 1);
secp256k1_sha256_write(&sha, x, 32);
secp256k1_sha256_finalize(&sha, output);
return 1;
}
const secp256k1_ecdh_hash_function secp256k1_ecdh_hash_function_sha256 = ecdh_hash_function_sha256;
const secp256k1_ecdh_hash_function secp256k1_ecdh_hash_function_default = ecdh_hash_function_sha256;
int secp256k1_ecdh(const secp256k1_context* ctx, unsigned char *output, const secp256k1_pubkey *point, const unsigned char *scalar, secp256k1_ecdh_hash_function hashfp) {
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(output != NULL);
ARG_CHECK(point != NULL);
ARG_CHECK(scalar != NULL);
if (hashfp == NULL) {
hashfp = secp256k1_ecdh_hash_function_default;
}
secp256k1_pubkey_load(ctx, &pt, point);
secp256k1_scalar_set_b32(&s, scalar, &overflow);
@@ -27,24 +45,18 @@ int secp256k1_ecdh(const secp256k1_context* ctx, unsigned char *result, const se
ret = 0;
} else {
unsigned char x[32];
unsigned char y[1];
secp256k1_sha256 sha;
unsigned char y[32];
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. */
/* Compute a hash of the point */
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_fe_get_b32(y, &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;
ret = hashfp(output, x, y);
}
secp256k1_scalar_clear(&s);

55
src/modules/ecdh/tests_impl.h
View File

@@ -7,6 +7,21 @@
#ifndef SECP256K1_MODULE_ECDH_TESTS_H
#define SECP256K1_MODULE_ECDH_TESTS_H
int ecdh_hash_function_test_fail(unsigned char *output, const unsigned char *x, const unsigned char *y) {
(void)output;
(void)x;
(void)y;
return 0;
}
int ecdh_hash_function_custom(unsigned char *output, const unsigned char *x, const unsigned char *y) {
/* Save x and y as uncompressed public key */
output[0] = 0x04;
memcpy(output + 1, x, 32);
memcpy(output + 33, y, 32);
return 1;
}
void test_ecdh_api(void) {
/* Setup context that just counts errors */
secp256k1_context *tctx = secp256k1_context_create(SECP256K1_CONTEXT_SIGN);
@@ -21,15 +36,15 @@ void test_ecdh_api(void) {
CHECK(secp256k1_ec_pubkey_create(tctx, &point, s_one) == 1);
/* Check all NULLs are detected */
CHECK(secp256k1_ecdh(tctx, res, &point, s_one) == 1);
CHECK(secp256k1_ecdh(tctx, res, &point, s_one, NULL) == 1);
CHECK(ecount == 0);
CHECK(secp256k1_ecdh(tctx, NULL, &point, s_one) == 0);
CHECK(secp256k1_ecdh(tctx, NULL, &point, s_one, NULL) == 0);
CHECK(ecount == 1);
CHECK(secp256k1_ecdh(tctx, res, NULL, s_one) == 0);
CHECK(secp256k1_ecdh(tctx, res, NULL, s_one, NULL) == 0);
CHECK(ecount == 2);
CHECK(secp256k1_ecdh(tctx, res, &point, NULL) == 0);
CHECK(secp256k1_ecdh(tctx, res, &point, NULL, NULL) == 0);
CHECK(ecount == 3);
CHECK(secp256k1_ecdh(tctx, res, &point, s_one) == 1);
CHECK(secp256k1_ecdh(tctx, res, &point, s_one, NULL) == 1);
CHECK(ecount == 3);
/* Cleanup */
@@ -46,27 +61,34 @@ void test_ecdh_generator_basepoint(void) {
for (i = 0; i < 100; ++i) {
secp256k1_sha256 sha;
unsigned char s_b32[32];
unsigned char output_ecdh[32];
unsigned char output_ecdh[65];
unsigned char output_ser[32];
unsigned char point_ser[33];
unsigned char point_ser[65];
size_t point_ser_len = sizeof(point_ser);
secp256k1_scalar s;
random_scalar_order(&s);
secp256k1_scalar_get_b32(s_b32, &s);
/* compute using ECDH function */
CHECK(secp256k1_ec_pubkey_create(ctx, &point[0], s_one) == 1);
CHECK(secp256k1_ecdh(ctx, output_ecdh, &point[0], s_b32) == 1);
/* compute "explicitly" */
CHECK(secp256k1_ec_pubkey_create(ctx, &point[1], s_b32) == 1);
/* compute using ECDH function with custom hash function */
CHECK(secp256k1_ecdh(ctx, output_ecdh, &point[0], s_b32, ecdh_hash_function_custom) == 1);
/* compute "explicitly" */
CHECK(secp256k1_ec_pubkey_serialize(ctx, point_ser, &point_ser_len, &point[1], SECP256K1_EC_UNCOMPRESSED) == 1);
/* compare */
CHECK(memcmp(output_ecdh, point_ser, 65) == 0);
/* compute using ECDH function with default hash function */
CHECK(secp256k1_ecdh(ctx, output_ecdh, &point[0], s_b32, NULL) == 1);
/* compute "explicitly" */
CHECK(secp256k1_ec_pubkey_serialize(ctx, point_ser, &point_ser_len, &point[1], SECP256K1_EC_COMPRESSED) == 1);
CHECK(point_ser_len == sizeof(point_ser));
secp256k1_sha256_initialize(&sha);
secp256k1_sha256_write(&sha, point_ser, point_ser_len);
secp256k1_sha256_finalize(&sha, output_ser);
/* compare */
CHECK(memcmp(output_ecdh, output_ser, sizeof(output_ser)) == 0);
CHECK(memcmp(output_ecdh, output_ser, 32) == 0);
}
}
@@ -89,11 +111,14 @@ void test_bad_scalar(void) {
CHECK(secp256k1_ec_pubkey_create(ctx, &point, s_rand) == 1);
/* Try to multiply it by bad values */
CHECK(secp256k1_ecdh(ctx, output, &point, s_zero) == 0);
CHECK(secp256k1_ecdh(ctx, output, &point, s_overflow) == 0);
CHECK(secp256k1_ecdh(ctx, output, &point, s_zero, NULL) == 0);
CHECK(secp256k1_ecdh(ctx, output, &point, s_overflow, NULL) == 0);
/* ...and a good one */
s_overflow[31] -= 1;
CHECK(secp256k1_ecdh(ctx, output, &point, s_overflow) == 1);
CHECK(secp256k1_ecdh(ctx, output, &point, s_overflow, NULL) == 1);
/* Hash function failure results in ecdh failure */
CHECK(secp256k1_ecdh(ctx, output, &point, s_overflow, ecdh_hash_function_test_fail) == 0);
}
void run_ecdh_tests(void) {