static int uECC_sign_with_k(const uint8_t *private_key,
                            const uint8_t *message_hash,
                            unsigned hash_size,
                            uECC_word_t *k,
                            uint8_t *signature,
                            uECC_Curve curve) {

    uECC_word_t tmp[uECC_MAX_WORDS];
    uECC_word_t s[uECC_MAX_WORDS];
    uECC_word_t *k2[2] = {tmp, s};
    uECC_word_t *initial_Z = 0;
#if uECC_VLI_NATIVE_LITTLE_ENDIAN
    uECC_word_t *p = (uECC_word_t *)signature;
#else
    uECC_word_t p[uECC_MAX_WORDS * 2];
#endif
    uECC_word_t carry;
    wordcount_t num_words = curve->num_words;
    wordcount_t num_n_words = BITS_TO_WORDS(curve->num_n_bits);
    bitcount_t num_n_bits = curve->num_n_bits;

    /* Make sure 0 < k < curve_n */
    if (uECC_vli_isZero(k, num_words) || uECC_vli_cmp(curve->n, k, num_n_words) != 1) {
        return 0;
    }

    carry = regularize_k(k, tmp, s, curve);
    /* If an RNG function was specified, try to get a random initial Z value to improve
       protection against side-channel attacks. */
    if (g_rng_function) {
        if (!uECC_generate_random_int(k2[carry], curve->p, num_words)) {
            return 0;
        }
        initial_Z = k2[carry];
    }
    EccPoint_mult(p, curve->G, k2[!carry], initial_Z, num_n_bits + 1, curve);
    if (uECC_vli_isZero(p, num_words)) {
        return 0;
    }

    /* If an RNG function was specified, get a random number
       to prevent side channel analysis of k. */
    if (!g_rng_function) {
        uECC_vli_clear(tmp, num_n_words);
        tmp[0] = 1;
    } else if (!uECC_generate_random_int(tmp, curve->n, num_n_words)) {
        return 0;
    }

    /* Prevent side channel analysis of uECC_vli_modInv() to determine
       bits of k / the private key by premultiplying by a random number */
    uECC_vli_modMult(k, k, tmp, curve->n, num_n_words); /* k' = rand * k */
    uECC_vli_modInv(k, k, curve->n, num_n_words);       /* k = 1 / k' */
    uECC_vli_modMult(k, k, tmp, curve->n, num_n_words); /* k = 1 / k */

#if uECC_VLI_NATIVE_LITTLE_ENDIAN == 0
    uECC_vli_nativeToBytes(signature, curve->num_bytes, p); /* store r */
#endif

#if uECC_VLI_NATIVE_LITTLE_ENDIAN
    bcopy((uint8_t *) tmp, private_key, BITS_TO_BYTES(curve->num_n_bits));
#else
    uECC_vli_bytesToNative(tmp, private_key, BITS_TO_BYTES(curve->num_n_bits)); /* tmp = d */
#endif

    s[num_n_words - 1] = 0;
    uECC_vli_set(s, p, num_words);
    uECC_vli_modMult(s, tmp, s, curve->n, num_n_words); /* s = r*d */

    bits2int(tmp, message_hash, hash_size, curve);
    uECC_vli_modAdd(s, tmp, s, curve->n, num_n_words); /* s = e + r*d */
    uECC_vli_modMult(s, s, k, curve->n, num_n_words);  /* s = (e + r*d) / k */
    if (uECC_vli_numBits(s, num_n_words) > (bitcount_t)curve->num_bytes * 8) {
        return 0;
    }
#if uECC_VLI_NATIVE_LITTLE_ENDIAN
    bcopy((uint8_t *) signature + curve->num_bytes, (uint8_t *) s, curve->num_bytes);
#else
    uECC_vli_nativeToBytes(signature + curve->num_bytes, curve->num_bytes, s);
#endif
    return 1;
}