bignum.h

// Copyright 2015-2016 Espressif Systems (Shanghai) PTE LTD
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at

//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
#ifndef __ESP_MBEDTLS_BIGNUM_H__
#define __ESP_MBEDTLS_BIGNUM_H__

#include_next "mbedtls/bignum.h"

/**
 * This is a wrapper for the main mbedtls/bignum.h. This wrapper
 * provides a few additional ESP32-only functions.
 *
 * This is because we don't set MBEDTLS_BIGNUM_ALT in the same way we
 * do for AES, SHA, etc. Because we still use most of the bignum.h
 * implementation and just replace a few hardware accelerated
 * functions (see MBEDTLS_MPI_EXP_MOD_ALT & MBEDTLS_MPI_MUL_MPI_ALT in
 * esp_config.h).
 *
 * @note Unlike the other hardware accelerator support functions in esp32/hwcrypto, there is no
 * generic "hwcrypto/bignum.h" header for using these functions without mbedTLS. The reason for this
 * is that all of the function implementations depend strongly upon the mbedTLS MPI implementation.
 */

/**
 * @brief Lock access to RSA Accelerator (MPI/bignum operations)
 *
 * RSA Accelerator hardware unit can only be used by one
 * consumer at a time.
 *
 * @note This function is non-recursive (do not call it twice from the
 * same task.)
 *
 * @note You do not need to call this if you are using the mbedTLS bignum.h
 * API or esp_mpi_xxx functions. This function is only needed if you
 * want to call ROM RSA functions or access the registers directly.
 *
 */
void esp_mpi_acquire_hardware(void);

/**
 * @brief Unlock access to RSA Accelerator (MPI/bignum operations)
 *
 * Has to be called once for each call to esp_mpi_acquire_hardware().
 *
 * @note You do not need to call this if you are using the mbedTLS bignum.h
 * API or esp_mpi_xxx functions. This function is only needed if you
 * want to call ROM RSA functions or access the registers directly.
 */
void esp_mpi_release_hardware(void);

/* @brief MPI modular mupltiplication function
 *
 * Calculates Z = (X * Y) mod M using MPI hardware acceleration.
 *
 * This is not part of the standard mbedTLS bignum API.
 *
 * @note All of X, Y & Z should be less than 4096 bit long or an error is returned.
 *
 * @param Z Result bignum, should be pre-initialised with mbedtls_mpi_init().
 * @param X First multiplication argument.
 * @param Y Second multiplication argument.
 * @param M Modulus value for result.
 *
 * @return 0 on success, mbedTLS MPI error codes on failure.
 */
int esp_mpi_mul_mpi_mod(mbedtls_mpi *Z, const mbedtls_mpi *X, const mbedtls_mpi *Y, const mbedtls_mpi *M);

#endif