library/psa_crypto_random_impl.h

/** \file psa_crypto_random_impl.h
 *
 * \brief PSA crypto random generator implementation abstraction.
 */
/*
 *  Copyright The Mbed TLS Contributors
 *  SPDX-License-Identifier: Apache-2.0
 *
 *  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 PSA_CRYPTO_RANDOM_IMPL_H
#define PSA_CRYPTO_RANDOM_IMPL_H

#if defined(MBEDTLS_PSA_CRYPTO_EXTERNAL_RNG)

#include <string.h>
#include <mbedtls/entropy.h> // only for error codes
#include <psa/crypto.h>

typedef mbedtls_psa_external_random_context_t mbedtls_psa_random_context_t;

/* Trivial wrapper around psa_generate_random(). */
int mbedtls_psa_get_random( void *p_rng,
                            unsigned char *output,
                            size_t output_size );

/* The PSA RNG API doesn't need any externally maintained state. */
#define MBEDTLS_PSA_RANDOM_STATE NULL

#else /* MBEDTLS_PSA_CRYPTO_EXTERNAL_RNG */

/* Choose a DRBG based on configuration and availability */
#if defined(MBEDTLS_PSA_HMAC_DRBG_MD_TYPE)

#include "mbedtls/hmac_drbg.h"

#elif defined(MBEDTLS_CTR_DRBG_C)

#include "mbedtls/ctr_drbg.h"

#elif defined(MBEDTLS_HMAC_DRBG_C)

#include "mbedtls/hmac_drbg.h"
#if defined(MBEDTLS_SHA512_C) && defined(MBEDTLS_SHA256_C)
#include <limits.h>
#if SIZE_MAX > 0xffffffff
/* Looks like a 64-bit system, so prefer SHA-512. */
#define MBEDTLS_PSA_HMAC_DRBG_MD_TYPE MBEDTLS_MD_SHA512
#else
/* Looks like a 32-bit system, so prefer SHA-256. */
#define MBEDTLS_PSA_HMAC_DRBG_MD_TYPE MBEDTLS_MD_SHA256
#endif
#elif defined(MBEDTLS_SHA512_C)
#define MBEDTLS_PSA_HMAC_DRBG_MD_TYPE MBEDTLS_MD_SHA512
#elif defined(MBEDTLS_SHA256_C)
#define MBEDTLS_PSA_HMAC_DRBG_MD_TYPE MBEDTLS_MD_SHA256
#else
#error "No hash algorithm available for HMAC_DBRG."
#endif

#else
#error "No DRBG module available for the psa_crypto module."
#endif

#include "mbedtls/entropy.h"

/** The type of the PSA DRBG context.
 */
#if defined(MBEDTLS_CTR_DRBG_C)
typedef mbedtls_ctr_drbg_context mbedtls_psa_drbg_context_t;
#elif defined(MBEDTLS_HMAC_DRBG_C)
typedef mbedtls_hmac_drbg_context mbedtls_psa_drbg_context_t;
#endif

/** Initialize the PSA DRBG.
 *
 * \param p_rng        Pointer to the Mbed TLS DRBG state.
 */
static inline void mbedtls_psa_drbg_init( mbedtls_psa_drbg_context_t *p_rng )
{
#if defined(MBEDTLS_CTR_DRBG_C)
    mbedtls_ctr_drbg_init( p_rng );
#elif defined(MBEDTLS_HMAC_DRBG_C)
    mbedtls_hmac_drbg_init( p_rng );
#endif
}

/** Deinitialize the PSA DRBG.
 *
 * \param p_rng        Pointer to the Mbed TLS DRBG state.
 */
static inline void mbedtls_psa_drbg_free( mbedtls_psa_drbg_context_t *p_rng )
{
#if defined(MBEDTLS_CTR_DRBG_C)
    mbedtls_ctr_drbg_free( p_rng );
#elif defined(MBEDTLS_HMAC_DRBG_C)
    mbedtls_hmac_drbg_free( p_rng );
#endif
}

/** The type of the PSA random generator context.
 *
 * The random generator context is composed of an entropy context and
 * a DRBG context.
 */
typedef struct
{
    void (* entropy_init )( mbedtls_entropy_context *ctx );
    void (* entropy_free )( mbedtls_entropy_context *ctx );
    mbedtls_entropy_context entropy;
    mbedtls_psa_drbg_context_t drbg;
} mbedtls_psa_random_context_t;

/* The type of an Mbed TLS random generator function. This should be
 * part of the public API instead of repeating the type everywhere.
 * For the time being, declare it here. Declaring a type is necessary
 * to define mbedtls_psa_get_random as a variable of a function pointer
 * type without incurring the wrath of check-names.sh. */
typedef int mbedtls_f_rng_t( void *p_rng, unsigned char *output, size_t output_size );

/** Return random data.
 *
 * This function is suitable as the \p f_rng parameter to Mbed TLS functions
 * that require a random generator. Use #MBEDTLS_PSA_RANDOM_STATE to
 * obtain the \p p_rng parameter.
 *
 * \param p_rng         The DRBG context. This must be
 *                      #MBEDTLS_PSA_RANDOM_STATE.
 * \param output        The buffer to fill.
 * \param output_len    The length of the buffer in bytes.
 *                      It must be at most #MBEDTLS_PSA_RANDOM_MAX_REQUEST.
 *
 * \retval              \c 0 on success.
 * \return              \c MBEDTLS_ERR_xxx_DRBG_xxx or
 *                      \c MBEDTLS_ERR_PLATFORM_xxx on failure.
 */
#if defined(MBEDTLS_CTR_DRBG_C)
static mbedtls_f_rng_t *const mbedtls_psa_get_random = mbedtls_ctr_drbg_random;
#elif defined(MBEDTLS_HMAC_DRBG_C)
static mbedtls_f_rng_t *const mbedtls_psa_get_random = mbedtls_hmac_drbg_random;
#endif

/** The maximum number of bytes that mbedtls_psa_get_random() is expected to
 * return.
 */
#if defined(MBEDTLS_CTR_DRBG_C)
#define MBEDTLS_PSA_RANDOM_MAX_REQUEST MBEDTLS_CTR_DRBG_MAX_REQUEST
#elif defined(MBEDTLS_HMAC_DRBG_C)
#define MBEDTLS_PSA_RANDOM_MAX_REQUEST MBEDTLS_HMAC_DRBG_MAX_REQUEST
#endif

/** A pointer to the PSA DRBG state.
 *
 * This variable is only intended to be used through the macro
 * #MBEDTLS_PSA_RANDOM_STATE.
 */
/* psa_crypto.c sets this variable to a pointer to the DRBG state in the
 * global PSA crypto state. */
extern mbedtls_psa_drbg_context_t *const mbedtls_psa_random_state;

/** A pointer to the PSA DRBG state.
 *
 * This macro expands to an expression that is suitable as the \c p_rng
 * parameter to pass to mbedtls_psa_get_random().
 *
 * This macro exists in all configurations where the psa_crypto module is
 * enabled. Its expansion depends on the configuration.
 */
#define MBEDTLS_PSA_RANDOM_STATE mbedtls_psa_random_state

/** Seed the PSA DRBG.
 *
 * \param entropy       An entropy context to read the seed from.
 * \param custom        The personalization string.
 *                      This can be \c NULL, in which case the personalization
 *                      string is empty regardless of the value of \p len.
 * \param len           The length of the personalization string.
 *
 * \return              \c 0 on success.
 * \return              An Mbed TLS error code (\c MBEDTLS_ERR_xxx) on failure.
 */
static inline int mbedtls_psa_drbg_seed(
    mbedtls_entropy_context *entropy,
    const unsigned char *custom, size_t len )
{
#if defined(MBEDTLS_CTR_DRBG_C)
    return( mbedtls_ctr_drbg_seed( MBEDTLS_PSA_RANDOM_STATE,
                                   mbedtls_entropy_func,
                                   entropy,
                                   custom, len ) );
#elif defined(MBEDTLS_HMAC_DRBG_C)
    const mbedtls_md_info_t *md_info =
        mbedtls_md_info_from_type( MBEDTLS_PSA_HMAC_DRBG_MD_TYPE );
    return( mbedtls_hmac_drbg_seed( MBEDTLS_PSA_RANDOM_STATE,
                                    md_info,
                                    mbedtls_entropy_func,
                                    entropy,
                                    custom, len ) );
#endif
}

#endif /* MBEDTLS_PSA_CRYPTO_EXTERNAL_RNG */

#endif /* PSA_CRYPTO_RANDOM_IMPL_H */