/*

 * Copyright 2019-2023 The OpenSSL Project Authors. All Rights Reserved.

 *

 * Licensed under the Apache License 2.0 (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

 */

#include "internal/ffc.h"

/*

 * See SP800-56Ar3 Section 5.6.2.3.1 : FFC Partial public key validation.

 * To only be used with ephemeral FFC public keys generated using the approved

 * safe-prime groups. (Checks that the public key is in the range [2, p - 1]

 *

 * ret contains 0 on success, or error flags (see FFC_ERROR_PUBKEY_TOO_SMALL)

 */

int ossl_ffc_validate_public_key_partial(const FFC_PARAMS *params,

                                         const BIGNUM *pub_key, int *ret)

{

    int ok = 0;

    BIGNUM *tmp = NULL;

    BN_CTX *ctx = NULL;

    *ret = 0;

    if (params == NULL || pub_key == NULL || params->p == NULL) {

        *ret = FFC_ERROR_PASSED_NULL_PARAM;

        return 0;

    }

    ctx = BN_CTX_new_ex(NULL);

    if (ctx == NULL)

        goto err;

    BN_CTX_start(ctx);

    tmp = BN_CTX_get(ctx);

    /* Step(1): Verify pub_key >= 2 */

    if (tmp == NULL

        || !BN_set_word(tmp, 1))

        goto err;

    if (BN_cmp(pub_key, tmp) <= 0) {

        *ret |= FFC_ERROR_PUBKEY_TOO_SMALL;

        goto err;

    }

    /* Step(1): Verify pub_key <=  p-2 */

    if (BN_copy(tmp, params->p) == NULL

        || !BN_sub_word(tmp, 1))

        goto err;

    if (BN_cmp(pub_key, tmp) >= 0) {

        *ret |= FFC_ERROR_PUBKEY_TOO_LARGE;

        goto err;

    }

    ok = 1;

 err:

    if (ctx != NULL) {

        BN_CTX_end(ctx);

        BN_CTX_free(ctx);

    }

    return ok;

}

/*

 * See SP800-56Ar3 Section 5.6.2.3.1 : FFC Full public key validation.

 */

int ossl_ffc_validate_public_key(const FFC_PARAMS *params,

                                 const BIGNUM *pub_key, int *ret)

{

    int ok = 0;

    BIGNUM *tmp = NULL;

    BN_CTX *ctx = NULL;

    if (!ossl_ffc_validate_public_key_partial(params, pub_key, ret))

        return 0;

    if (params->q != NULL) {

        ctx = BN_CTX_new_ex(NULL);

        if (ctx == NULL)

            goto err;

        BN_CTX_start(ctx);

        tmp = BN_CTX_get(ctx);

        /* Check pub_key^q == 1 mod p */

        if (tmp == NULL

            || !BN_mod_exp(tmp, pub_key, params->q, params->p, ctx))

            goto err;

        if (!BN_is_one(tmp)) {

            *ret |= FFC_ERROR_PUBKEY_INVALID;

            goto err;

        }

    }

    ok = 1;

 err:

    if (ctx != NULL) {

        BN_CTX_end(ctx);

        BN_CTX_free(ctx);

    }

    return ok;

}

/*

 * See SP800-56Ar3 Section 5.6.2.1.2: Owner assurance of Private key validity.

 * Verifies priv_key is in the range [1..upper-1]. The passed in value of upper

 * is normally params->q but can be 2^N for approved safe prime groups.

 * Note: This assumes that the domain parameters are valid.

 */

int ossl_ffc_validate_private_key(const BIGNUM *upper, const BIGNUM *priv,

                                  int *ret)

{

    int ok = 0;

    *ret = 0;

    if (priv == NULL || upper == NULL) {

        *ret = FFC_ERROR_PASSED_NULL_PARAM;

        goto err;

    }

    if (BN_cmp(priv, BN_value_one()) < 0) {

        *ret |= FFC_ERROR_PRIVKEY_TOO_SMALL;

        goto err;

    }

    if (BN_cmp(priv, upper) >= 0) {

        *ret |= FFC_ERROR_PRIVKEY_TOO_LARGE;

        goto err;

    }

    ok = 1;

err:

    return ok;

}