/* ec_dsa.c - TinyCrypt implementation of EC-DSA */

/*  Copyright (c) 2014, Kenneth MacKay
    All rights reserved.

    Redistribution and use in source and binary forms, with or without
    modification, are permitted provided that the following conditions are met:
 *  * Redistributions of source code must retain the above copyright notice,
      this list of conditions and the following disclaimer.
 *  * Redistributions in binary form must reproduce the above copyright notice,
      this list of conditions and the following disclaimer in the documentation
      and/or other materials provided with the distribution.

    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
    AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
    IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
    ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
    LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
    CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
    SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
    INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
    CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
    ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
    POSSIBILITY OF SUCH DAMAGE.*/

/*
    Copyright (C) 2017 by Intel Corporation, All Rights Reserved.

    Redistribution and use in source and binary forms, with or without
    modification, are permitted provided that the following conditions are met:

      - Redistributions of source code must retain the above copyright notice,
       this list of conditions and the following disclaimer.

      - Redistributions in binary form must reproduce the above copyright
      notice, this list of conditions and the following disclaimer in the
      documentation and/or other materials provided with the distribution.

      - Neither the name of Intel Corporation nor the names of its contributors
      may be used to endorse or promote products derived from this software
      without specific prior written permission.

    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
    AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
    IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
    ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
    LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
    CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
    SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
    INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
    CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
    ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
    POSSIBILITY OF SUCH DAMAGE.
*/

#include <tinycrypt/constants.h>
#include <tinycrypt/ecc.h>
#include <tinycrypt/ecc_dsa.h>

#if default_RNG_defined
    static uECC_RNG_Function g_rng_function = &default_CSPRNG;
#else
    static uECC_RNG_Function g_rng_function = 0;
#endif

static void bits2int(uECC_word_t* native, const uint8_t* bits,
                     unsigned bits_size, uECC_Curve curve)
{
    unsigned num_n_bytes = BITS_TO_BYTES(curve->num_n_bits);
    unsigned num_n_words = BITS_TO_WORDS(curve->num_n_bits);
    int shift;
    uECC_word_t carry;
    uECC_word_t* ptr;

    if (bits_size > num_n_bytes)
    {
        bits_size = num_n_bytes;
    }

    uECC_vli_clear(native, num_n_words);
    uECC_vli_bytesToNative(native, bits, bits_size);

    if (bits_size * 8 <= (unsigned)curve->num_n_bits)
    {
        return;
    }

    shift = bits_size * 8 - curve->num_n_bits;
    carry = 0;
    ptr = native + num_n_words;

    while (ptr-- > native)
    {
        uECC_word_t temp = *ptr;
        *ptr = (temp >> shift) | carry;
        carry = temp << (uECC_WORD_BITS - shift);
    }

    /* Reduce mod curve_n */
    if (uECC_vli_cmp_unsafe(curve->n, native, num_n_words) != 1)
    {
        uECC_vli_sub(native, native, curve->n, num_n_words);
    }
}

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[NUM_ECC_WORDS];
    uECC_word_t s[NUM_ECC_WORDS];
    uECC_word_t* k2[2] = {tmp, s};
    uECC_word_t p[NUM_ECC_WORDS * 2];
    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);
    EccPoint_mult(p, curve->G, k2[!carry], 0, 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 */
    uECC_vli_nativeToBytes(signature, curve->num_bytes, p); /* store r */
    /* tmp = d: */
    uECC_vli_bytesToNative(tmp, private_key, BITS_TO_BYTES(curve->num_n_bits));
    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;
    }

    uECC_vli_nativeToBytes(signature + curve->num_bytes, curve->num_bytes, s);
    return 1;
}

int uECC_sign(const uint8_t* private_key, const uint8_t* message_hash,
              unsigned hash_size, uint8_t* signature, uECC_Curve curve)
{
    uECC_word_t _random[2*NUM_ECC_WORDS];
    uECC_word_t k[NUM_ECC_WORDS];
    uECC_word_t tries;

    for (tries = 0; tries < uECC_RNG_MAX_TRIES; ++tries)
    {
        /* Generating _random uniformly at random: */
        uECC_RNG_Function rng_function = uECC_get_rng();

        if (!rng_function ||
                !rng_function((uint8_t*)_random, 2*NUM_ECC_WORDS*uECC_WORD_SIZE))
        {
            return 0;
        }

        // computing k as modular reduction of _random (see FIPS 186.4 B.5.1):
        uECC_vli_mmod(k, _random, curve->n, BITS_TO_WORDS(curve->num_n_bits));

        if (uECC_sign_with_k(private_key, message_hash, hash_size, k, signature,
                             curve))
        {
            return 1;
        }
    }

    return 0;
}

static bitcount_t smax(bitcount_t a, bitcount_t b)
{
    return (a > b ? a : b);
}

int uECC_verify(const uint8_t* public_key, const uint8_t* message_hash,
                unsigned hash_size, const uint8_t* signature,
                uECC_Curve curve)
{
    uECC_word_t u1[NUM_ECC_WORDS], u2[NUM_ECC_WORDS];
    uECC_word_t z[NUM_ECC_WORDS];
    uECC_word_t sum[NUM_ECC_WORDS * 2];
    uECC_word_t rx[NUM_ECC_WORDS];
    uECC_word_t ry[NUM_ECC_WORDS];
    uECC_word_t tx[NUM_ECC_WORDS];
    uECC_word_t ty[NUM_ECC_WORDS];
    uECC_word_t tz[NUM_ECC_WORDS];
    const uECC_word_t* points[4];
    const uECC_word_t* point;
    bitcount_t num_bits;
    bitcount_t i;
    uECC_word_t _public[NUM_ECC_WORDS * 2];
    uECC_word_t r[NUM_ECC_WORDS], s[NUM_ECC_WORDS];
    wordcount_t num_words = curve->num_words;
    wordcount_t num_n_words = BITS_TO_WORDS(curve->num_n_bits);
    rx[num_n_words - 1] = 0;
    r[num_n_words - 1] = 0;
    s[num_n_words - 1] = 0;
    uECC_vli_bytesToNative(_public, public_key, curve->num_bytes);
    uECC_vli_bytesToNative(_public + num_words, public_key + curve->num_bytes,
                           curve->num_bytes);
    uECC_vli_bytesToNative(r, signature, curve->num_bytes);
    uECC_vli_bytesToNative(s, signature + curve->num_bytes, curve->num_bytes);

    /* r, s must not be 0. */
    if (uECC_vli_isZero(r, num_words) || uECC_vli_isZero(s, num_words))
    {
        return 0;
    }

    /* r, s must be < n. */
    if (uECC_vli_cmp_unsafe(curve->n, r, num_n_words) != 1 ||
            uECC_vli_cmp_unsafe(curve->n, s, num_n_words) != 1)
    {
        return 0;
    }

    /* Calculate u1 and u2. */
    uECC_vli_modInv(z, s, curve->n, num_n_words); /* z = 1/s */
    u1[num_n_words - 1] = 0;
    bits2int(u1, message_hash, hash_size, curve);
    uECC_vli_modMult(u1, u1, z, curve->n, num_n_words); /* u1 = e/s */
    uECC_vli_modMult(u2, r, z, curve->n, num_n_words); /* u2 = r/s */
    /* Calculate sum = G + Q. */
    uECC_vli_set(sum, _public, num_words);
    uECC_vli_set(sum + num_words, _public + num_words, num_words);
    uECC_vli_set(tx, curve->G, num_words);
    uECC_vli_set(ty, curve->G + num_words, num_words);
    uECC_vli_modSub(z, sum, tx, curve->p, num_words); /* z = x2 - x1 */
    XYcZ_add(tx, ty, sum, sum + num_words, curve);
    uECC_vli_modInv(z, z, curve->p, num_words); /* z = 1/z */
    apply_z(sum, sum + num_words, z, curve);
    /* Use Shamir's trick to calculate u1*G + u2*Q */
    points[0] = 0;
    points[1] = curve->G;
    points[2] = _public;
    points[3] = sum;
    num_bits = smax(uECC_vli_numBits(u1, num_n_words),
                    uECC_vli_numBits(u2, num_n_words));
    point = points[(!!uECC_vli_testBit(u1, num_bits - 1)) |
                                                          ((!!uECC_vli_testBit(u2, num_bits - 1)) << 1)];
    uECC_vli_set(rx, point, num_words);
    uECC_vli_set(ry, point + num_words, num_words);
    uECC_vli_clear(z, num_words);
    z[0] = 1;

    for (i = num_bits - 2; i >= 0; --i)
    {
        uECC_word_t index;
        curve->double_jacobian(rx, ry, z, curve);
        index = (!!uECC_vli_testBit(u1, i)) | ((!!uECC_vli_testBit(u2, i)) << 1);
        point = points[index];

        if (point)
        {
            uECC_vli_set(tx, point, num_words);
            uECC_vli_set(ty, point + num_words, num_words);
            apply_z(tx, ty, z, curve);
            uECC_vli_modSub(tz, rx, tx, curve->p, num_words); /* Z = x2 - x1 */
            XYcZ_add(tx, ty, rx, ry, curve);
            uECC_vli_modMult_fast(z, z, tz, curve);
        }
    }

    uECC_vli_modInv(z, z, curve->p, num_words); /* Z = 1/Z */
    apply_z(rx, ry, z, curve);

    /* v = x1 (mod n) */
    if (uECC_vli_cmp_unsafe(curve->n, rx, num_n_words) != 1)
    {
        uECC_vli_sub(rx, rx, curve->n, num_n_words);
    }

    /* Accept only if v == r. */
    return (int)(uECC_vli_equal(rx, r, num_words) == 0);
}

