tests_impl.h

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/**********************************************************************
 * 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_TESTS_
#define _SECP256K1_MODULE_ECDH_TESTS_

void test_ecdh_generator_basepoint(void) {
    unsigned char s_one[32] = { 0 };
    secp256k1_pubkey point[2];
    int i;

    s_one[31] = 1;
    /* Check against pubkey creation when the basepoint is the generator */
    for (i = 0; i < 100; ++i) {
        secp256k1_sha256_t sha;
        unsigned char s_b32[32];
        unsigned char output_ecdh[32];
        unsigned char output_ser[32];
        unsigned char point_ser[33];
        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);
        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);
    }
}

void test_bad_scalar(void) {
    unsigned char s_zero[32] = { 0 };
    unsigned char s_overflow[32] = {
        0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
        0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xfe,
        0xba, 0xae, 0xdc, 0xe6, 0xaf, 0x48, 0xa0, 0x3b,
        0xbf, 0xd2, 0x5e, 0x8c, 0xd0, 0x36, 0x41, 0x41
    };
    unsigned char s_rand[32] = { 0 };
    unsigned char output[32];
    secp256k1_scalar rand;
    secp256k1_pubkey point;

    /* Create random point */
    random_scalar_order(&rand);
    secp256k1_scalar_get_b32(s_rand, &rand);
    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);
    /* ...and a good one */
    s_overflow[31] -= 1;
    CHECK(secp256k1_ecdh(ctx, output, &point, s_overflow) == 1);
}

void run_ecdh_tests(void) {
    test_ecdh_generator_basepoint();
    test_bad_scalar();
}

#endif