/*

 * Copyright 2017-2018 The OpenSSL Project Authors. All Rights Reserved.

 * Copyright 2015-2016 Cryptography Research, Inc.

 *

 * Licensed under the OpenSSL license (the "License").  You may not use

 * this file except in compliance with the License.  You can obtain a copy

 * in the file LICENSE in the source distribution or at

 * https://www.openssl.org/source/license.html

 *

 * Originally written by Mike Hamburg

 */

#include <string.h>

#include <openssl/crypto.h>

#include <openssl/evp.h>

#include "curve448_lcl.h"

#include "word.h"

#include "ed448.h"

#include "internal/numbers.h"

#define COFACTOR 4

static c448_error_t oneshot_hash(uint8_t *out, size_t outlen,

                                 const uint8_t *in, size_t inlen)

{

    EVP_MD_CTX *hashctx = EVP_MD_CTX_new();

    if (hashctx == NULL)

        return C448_FAILURE;

    if (!EVP_DigestInit_ex(hashctx, EVP_shake256(), NULL)

            || !EVP_DigestUpdate(hashctx, in, inlen)

            || !EVP_DigestFinalXOF(hashctx, out, outlen)) {

        EVP_MD_CTX_free(hashctx);

        return C448_FAILURE;

    }

    EVP_MD_CTX_free(hashctx);

    return C448_SUCCESS;

}

static void clamp(uint8_t secret_scalar_ser[EDDSA_448_PRIVATE_BYTES])

{

    secret_scalar_ser[0] &= -COFACTOR;

    secret_scalar_ser[EDDSA_448_PRIVATE_BYTES - 1] = 0;

    secret_scalar_ser[EDDSA_448_PRIVATE_BYTES - 2] |= 0x80;

}

static c448_error_t hash_init_with_dom(EVP_MD_CTX *hashctx, uint8_t prehashed,

                                       uint8_t for_prehash,

                                       const uint8_t *context,

                                       size_t context_len)

{

    const char *dom_s = "SigEd448";

    uint8_t dom[2];

    if (context_len > UINT8_MAX)

        return C448_FAILURE;

    dom[0] = (uint8_t)(2 - (prehashed == 0 ? 1 : 0)

                       - (for_prehash == 0 ? 1 : 0));

    dom[1] = (uint8_t)context_len;

    if (!EVP_DigestInit_ex(hashctx, EVP_shake256(), NULL)

            || !EVP_DigestUpdate(hashctx, dom_s, strlen(dom_s))

            || !EVP_DigestUpdate(hashctx, dom, sizeof(dom))

            || !EVP_DigestUpdate(hashctx, context, context_len))

        return C448_FAILURE;

    return C448_SUCCESS;

}

/* In this file because it uses the hash */

c448_error_t c448_ed448_convert_private_key_to_x448(

                            uint8_t x[X448_PRIVATE_BYTES],

                            const uint8_t ed [EDDSA_448_PRIVATE_BYTES])

{

    /* pass the private key through oneshot_hash function */

    /* and keep the first X448_PRIVATE_BYTES bytes */

    return oneshot_hash(x, X448_PRIVATE_BYTES, ed,

                        EDDSA_448_PRIVATE_BYTES);

}

c448_error_t c448_ed448_derive_public_key(

                        uint8_t pubkey[EDDSA_448_PUBLIC_BYTES],

                        const uint8_t privkey[EDDSA_448_PRIVATE_BYTES])

{

    /* only this much used for keygen */

    uint8_t secret_scalar_ser[EDDSA_448_PRIVATE_BYTES];

    curve448_scalar_t secret_scalar;

    unsigned int c;

    curve448_point_t p;

    if (!oneshot_hash(secret_scalar_ser, sizeof(secret_scalar_ser), privkey,

                      EDDSA_448_PRIVATE_BYTES))

        return C448_FAILURE;

    clamp(secret_scalar_ser);

    curve448_scalar_decode_long(secret_scalar, secret_scalar_ser,

                                sizeof(secret_scalar_ser));

    /*

     * Since we are going to mul_by_cofactor during encoding, divide by it

     * here. However, the EdDSA base point is not the same as the decaf base

     * point if the sigma isogeny is in use: the EdDSA base point is on

     * Etwist_d/(1-d) and the decaf base point is on Etwist_d, and when

     * converted it effectively picks up a factor of 2 from the isogenies.  So

     * we might start at 2 instead of 1.

     */

    for (c = 1; c < C448_EDDSA_ENCODE_RATIO; c <<= 1)

        curve448_scalar_halve(secret_scalar, secret_scalar);

    curve448_precomputed_scalarmul(p, curve448_precomputed_base, secret_scalar);

    curve448_point_mul_by_ratio_and_encode_like_eddsa(pubkey, p);

    /* Cleanup */

    curve448_scalar_destroy(secret_scalar);

    curve448_point_destroy(p);

    OPENSSL_cleanse(secret_scalar_ser, sizeof(secret_scalar_ser));

    return C448_SUCCESS;

}

c448_error_t c448_ed448_sign(

                        uint8_t signature[EDDSA_448_SIGNATURE_BYTES],

                        const uint8_t privkey[EDDSA_448_PRIVATE_BYTES],

                        const uint8_t pubkey[EDDSA_448_PUBLIC_BYTES],

                        const uint8_t *message, size_t message_len,

                        uint8_t prehashed, const uint8_t *context,

                        size_t context_len)

{

    curve448_scalar_t secret_scalar;

    EVP_MD_CTX *hashctx = EVP_MD_CTX_new();

    c448_error_t ret = C448_FAILURE;

    curve448_scalar_t nonce_scalar;

    uint8_t nonce_point[EDDSA_448_PUBLIC_BYTES] = { 0 };

    unsigned int c;

    curve448_scalar_t challenge_scalar;

    if (hashctx == NULL)

        return C448_FAILURE;

    {

        /*

         * Schedule the secret key, First EDDSA_448_PRIVATE_BYTES is serialised

         * secret scalar,next EDDSA_448_PRIVATE_BYTES bytes is the seed.

         */

        uint8_t expanded[EDDSA_448_PRIVATE_BYTES * 2];

        if (!oneshot_hash(expanded, sizeof(expanded), privkey,

                          EDDSA_448_PRIVATE_BYTES))

            goto err;

        clamp(expanded);

        curve448_scalar_decode_long(secret_scalar, expanded,

                                    EDDSA_448_PRIVATE_BYTES);

        /* Hash to create the nonce */

        if (!hash_init_with_dom(hashctx, prehashed, 0, context, context_len)

                || !EVP_DigestUpdate(hashctx,

                                     expanded + EDDSA_448_PRIVATE_BYTES,

                                     EDDSA_448_PRIVATE_BYTES)

                || !EVP_DigestUpdate(hashctx, message, message_len)) {

            OPENSSL_cleanse(expanded, sizeof(expanded));

            goto err;

        }

        OPENSSL_cleanse(expanded, sizeof(expanded));

    }

    /* Decode the nonce */

    {

        uint8_t nonce[2 * EDDSA_448_PRIVATE_BYTES];

        if (!EVP_DigestFinalXOF(hashctx, nonce, sizeof(nonce)))

            goto err;

        curve448_scalar_decode_long(nonce_scalar, nonce, sizeof(nonce));

        OPENSSL_cleanse(nonce, sizeof(nonce));

    }

    {

        /* Scalarmul to create the nonce-point */

        curve448_scalar_t nonce_scalar_2;

        curve448_point_t p;

        curve448_scalar_halve(nonce_scalar_2, nonce_scalar);

        for (c = 2; c < C448_EDDSA_ENCODE_RATIO; c <<= 1)

            curve448_scalar_halve(nonce_scalar_2, nonce_scalar_2);

        curve448_precomputed_scalarmul(p, curve448_precomputed_base,

                                       nonce_scalar_2);

        curve448_point_mul_by_ratio_and_encode_like_eddsa(nonce_point, p);

        curve448_point_destroy(p);

        curve448_scalar_destroy(nonce_scalar_2);

    }

    {

        uint8_t challenge[2 * EDDSA_448_PRIVATE_BYTES];

        /* Compute the challenge */

        if (!hash_init_with_dom(hashctx, prehashed, 0, context, context_len)

                || !EVP_DigestUpdate(hashctx, nonce_point, sizeof(nonce_point))

                || !EVP_DigestUpdate(hashctx, pubkey, EDDSA_448_PUBLIC_BYTES)

                || !EVP_DigestUpdate(hashctx, message, message_len)

                || !EVP_DigestFinalXOF(hashctx, challenge, sizeof(challenge)))

            goto err;

        curve448_scalar_decode_long(challenge_scalar, challenge,

                                    sizeof(challenge));

        OPENSSL_cleanse(challenge, sizeof(challenge));

    }

    curve448_scalar_mul(challenge_scalar, challenge_scalar, secret_scalar);

    curve448_scalar_add(challenge_scalar, challenge_scalar, nonce_scalar);

    OPENSSL_cleanse(signature, EDDSA_448_SIGNATURE_BYTES);

    memcpy(signature, nonce_point, sizeof(nonce_point));

    curve448_scalar_encode(&signature[EDDSA_448_PUBLIC_BYTES],

                           challenge_scalar);

    curve448_scalar_destroy(secret_scalar);

    curve448_scalar_destroy(nonce_scalar);

    curve448_scalar_destroy(challenge_scalar);

    ret = C448_SUCCESS;

 err:

    EVP_MD_CTX_free(hashctx);

    return ret;

}

c448_error_t c448_ed448_sign_prehash(

                        uint8_t signature[EDDSA_448_SIGNATURE_BYTES],

                        const uint8_t privkey[EDDSA_448_PRIVATE_BYTES],

                        const uint8_t pubkey[EDDSA_448_PUBLIC_BYTES],

                        const uint8_t hash[64], const uint8_t *context,

                        size_t context_len)

{

    return c448_ed448_sign(signature, privkey, pubkey, hash, 64, 1, context,

                           context_len);

}

c448_error_t c448_ed448_verify(

                    const uint8_t signature[EDDSA_448_SIGNATURE_BYTES],

                    const uint8_t pubkey[EDDSA_448_PUBLIC_BYTES],

                    const uint8_t *message, size_t message_len,

                    uint8_t prehashed, const uint8_t *context,

                    uint8_t context_len)

{

    curve448_point_t pk_point, r_point;

    c448_error_t error =

        curve448_point_decode_like_eddsa_and_mul_by_ratio(pk_point, pubkey);

    curve448_scalar_t challenge_scalar;

    curve448_scalar_t response_scalar;

    if (C448_SUCCESS != error)

        return error;

    error =

        curve448_point_decode_like_eddsa_and_mul_by_ratio(r_point, signature);

    if (C448_SUCCESS != error)

        return error;

    {

        /* Compute the challenge */

        EVP_MD_CTX *hashctx = EVP_MD_CTX_new();

        uint8_t challenge[2 * EDDSA_448_PRIVATE_BYTES];

        if (hashctx == NULL

                || !hash_init_with_dom(hashctx, prehashed, 0, context,

                                       context_len)

                || !EVP_DigestUpdate(hashctx, signature, EDDSA_448_PUBLIC_BYTES)

                || !EVP_DigestUpdate(hashctx, pubkey, EDDSA_448_PUBLIC_BYTES)

                || !EVP_DigestUpdate(hashctx, message, message_len)

                || !EVP_DigestFinalXOF(hashctx, challenge, sizeof(challenge))) {

            EVP_MD_CTX_free(hashctx);

            return C448_FAILURE;

        }

        EVP_MD_CTX_free(hashctx);

        curve448_scalar_decode_long(challenge_scalar, challenge,

                                    sizeof(challenge));

        OPENSSL_cleanse(challenge, sizeof(challenge));

    }

    curve448_scalar_sub(challenge_scalar, curve448_scalar_zero,

                        challenge_scalar);

    curve448_scalar_decode_long(response_scalar,

                                &signature[EDDSA_448_PUBLIC_BYTES],

                                EDDSA_448_PRIVATE_BYTES);

    /* pk_point = -c(x(P)) + (cx + k)G = kG */

    curve448_base_double_scalarmul_non_secret(pk_point,

                                              response_scalar,

                                              pk_point, challenge_scalar);

    return c448_succeed_if(curve448_point_eq(pk_point, r_point));

}

c448_error_t c448_ed448_verify_prehash(

                    const uint8_t signature[EDDSA_448_SIGNATURE_BYTES],

                    const uint8_t pubkey[EDDSA_448_PUBLIC_BYTES],

                    const uint8_t hash[64], const uint8_t *context,

                    uint8_t context_len)

{

    return c448_ed448_verify(signature, pubkey, hash, 64, 1, context,

                             context_len);

}

int ED448_sign(uint8_t *out_sig, const uint8_t *message, size_t message_len,

               const uint8_t public_key[57], const uint8_t private_key[57],

               const uint8_t *context, size_t context_len)

{

    return c448_ed448_sign(out_sig, private_key, public_key, message,

                           message_len, 0, context, context_len)

        == C448_SUCCESS;

}

int ED448_verify(const uint8_t *message, size_t message_len,

                 const uint8_t signature[114], const uint8_t public_key[57],

                 const uint8_t *context, size_t context_len)

{

    return c448_ed448_verify(signature, public_key, message, message_len, 0,

                             context, (uint8_t)context_len) == C448_SUCCESS;

}

int ED448ph_sign(uint8_t *out_sig, const uint8_t hash[64],

                 const uint8_t public_key[57], const uint8_t private_key[57],

                 const uint8_t *context, size_t context_len)

{

    return c448_ed448_sign_prehash(out_sig, private_key, public_key, hash,

                                   context, context_len) == C448_SUCCESS;

}

int ED448ph_verify(const uint8_t hash[64], const uint8_t signature[114],

                   const uint8_t public_key[57], const uint8_t *context,

                   size_t context_len)

{

    return c448_ed448_verify_prehash(signature, public_key, hash, context,

                                     (uint8_t)context_len) == C448_SUCCESS;

}

int ED448_public_from_private(uint8_t out_public_key[57],

                              const uint8_t private_key[57])

{

    return c448_ed448_derive_public_key(out_public_key, private_key)

        == C448_SUCCESS;

}