include/mbedtls/hmac_drbg.h

/**
 * \file hmac_drbg.h
 *
 * \brief The HMAC_DRBG pseudorandom generator.
 *
 * This module implements the HMAC_DRBG pseudorandom generator described
 * in <em>NIST SP 800-90A: Recommendation for Random Number Generation Using
 * Deterministic Random Bit Generators</em>.
 */
/*
 *  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 MBEDTLS_HMAC_DRBG_H
#define MBEDTLS_HMAC_DRBG_H
#include "mbedtls/private_access.h"

#include "mbedtls/build_info.h"

#include "mbedtls/md.h"

#if defined(MBEDTLS_THREADING_C)
#    include "mbedtls/threading.h"
#endif

/*
 * Error codes
 */
/** Too many random requested in single call. */
#define MBEDTLS_ERR_HMAC_DRBG_REQUEST_TOO_BIG -0x0003
/** Input too large (Entropy + additional). */
#define MBEDTLS_ERR_HMAC_DRBG_INPUT_TOO_BIG -0x0005
/** Read/write error in file. */
#define MBEDTLS_ERR_HMAC_DRBG_FILE_IO_ERROR -0x0007
/** The entropy source failed. */
#define MBEDTLS_ERR_HMAC_DRBG_ENTROPY_SOURCE_FAILED -0x0009

/**
 * \name SECTION: Module settings
 *
 * The configuration options you can set for this module are in this section.
 * Either change them in mbedtls_config.h or define them on the compiler command
 * line.
 * \{
 */

#if !defined(MBEDTLS_HMAC_DRBG_RESEED_INTERVAL)
/** Interval before reseed is performed by default */
#    define MBEDTLS_HMAC_DRBG_RESEED_INTERVAL 10000
#endif

#if !defined(MBEDTLS_HMAC_DRBG_MAX_INPUT)
/** Maximum number of additional input bytes */
#    define MBEDTLS_HMAC_DRBG_MAX_INPUT 256
#endif

#if !defined(MBEDTLS_HMAC_DRBG_MAX_REQUEST)
/** Maximum number of requested bytes per call */
#    define MBEDTLS_HMAC_DRBG_MAX_REQUEST 1024
#endif

#if !defined(MBEDTLS_HMAC_DRBG_MAX_SEED_INPUT)
/** Maximum size of (re)seed buffer */
#    define MBEDTLS_HMAC_DRBG_MAX_SEED_INPUT 384
#endif

/* \} name SECTION: Module settings */

/** No prediction resistance       */
#define MBEDTLS_HMAC_DRBG_PR_OFF 0
/** Prediction resistance enabled  */
#define MBEDTLS_HMAC_DRBG_PR_ON 1

#ifdef __cplusplus
extern "C" {
#endif

/**
 * HMAC_DRBG context.
 */
typedef struct mbedtls_hmac_drbg_context {
    /* Working state: the key K is not stored explicitly,
     * but is implied by the HMAC context */
    mbedtls_md_context_t MBEDTLS_PRIVATE(md_ctx); /*!< HMAC context (inc. K)  */
    unsigned char MBEDTLS_PRIVATE(V)[MBEDTLS_MD_MAX_SIZE]; /*!< V in the spec */
    int MBEDTLS_PRIVATE(reseed_counter); /*!< reseed counter         */

    /* Administrative state */
    size_t MBEDTLS_PRIVATE(entropy_len); /*!< entropy bytes grabbed on each
                                            (re)seed */
    int MBEDTLS_PRIVATE(prediction_resistance); /*!< enable prediction
                                    resistance (Automatic reseed before every
                                    random generation) */
    int MBEDTLS_PRIVATE(reseed_interval); /*!< reseed interval   */

    /* Callbacks */
    int (*MBEDTLS_PRIVATE(f_entropy))(void *,
                                      unsigned char *,
                                      size_t); /*!<
                                                  entropy
                                                  function
                                                */
    void *MBEDTLS_PRIVATE(p_entropy); /*!< context for the entropy function */

#if defined(MBEDTLS_THREADING_C)
    /* Invariant: the mutex is initialized if and only if
     * md_ctx->md_info != NULL. This means that the mutex is initialized
     * during the initial seeding in mbedtls_hmac_drbg_seed() or
     * mbedtls_hmac_drbg_seed_buf() and freed in mbedtls_ctr_drbg_free().
     *
     * Note that this invariant may change without notice. Do not rely on it
     * and do not access the mutex directly in application code.
     */
    mbedtls_threading_mutex_t MBEDTLS_PRIVATE(mutex);
#endif
} mbedtls_hmac_drbg_context;

/**
 * \brief               HMAC_DRBG context initialization.
 *
 * This function makes the context ready for mbedtls_hmac_drbg_seed(),
 * mbedtls_hmac_drbg_seed_buf() or mbedtls_hmac_drbg_free().
 *
 * \note                The reseed interval is
 * #MBEDTLS_HMAC_DRBG_RESEED_INTERVAL
 *                      by default. Override this value by calling
 *                      mbedtls_hmac_drbg_set_reseed_interval().
 *
 * \param ctx           HMAC_DRBG context to be initialized.
 */
void mbedtls_hmac_drbg_init(mbedtls_hmac_drbg_context *ctx);

/**
 * \brief               HMAC_DRBG initial seeding.
 *
 * Set the initial seed and set up the entropy source for future reseeds.
 *
 * A typical choice for the \p f_entropy and \p p_entropy parameters is
 * to use the entropy module:
 * - \p f_entropy is mbedtls_entropy_func();
 * - \p p_entropy is an instance of ::mbedtls_entropy_context initialized
 *   with mbedtls_entropy_init() (which registers the platform's default
 *   entropy sources).
 *
 * You can provide a personalization string in addition to the
 * entropy source, to make this instantiation as unique as possible.
 *
 * \note                By default, the security strength as defined by NIST is:
 *                      - 128 bits if \p md_info is SHA-1;
 *                      - 192 bits if \p md_info is SHA-224;
 *                      - 256 bits if \p md_info is SHA-256, SHA-384 or SHA-512.
 *                      Note that SHA-256 is just as efficient as SHA-224.
 *                      The security strength can be reduced if a smaller
 *                      entropy length is set with
 *                      mbedtls_hmac_drbg_set_entropy_len().
 *
 * \note                The default entropy length is the security strength
 *                      (converted from bits to bytes). You can override
 *                      it by calling mbedtls_hmac_drbg_set_entropy_len().
 *
 * \note                During the initial seeding, this function calls
 *                      the entropy source to obtain a nonce
 *                      whose length is half the entropy length.
 */
#if defined(MBEDTLS_THREADING_C)
/**
 * \note                When Mbed TLS is built with threading support,
 *                      after this function returns successfully,
 *                      it is safe to call mbedtls_hmac_drbg_random()
 *                      from multiple threads. Other operations, including
 *                      reseeding, are not thread-safe.
 */
#endif /* MBEDTLS_THREADING_C */
/**
 * \param ctx           HMAC_DRBG context to be seeded.
 * \param md_info       MD algorithm to use for HMAC_DRBG.
 * \param f_entropy     The entropy callback, taking as arguments the
 *                      \p p_entropy context, the buffer to fill, and the
 *                      length of the buffer.
 *                      \p f_entropy is always called with a length that is
 *                      less than or equal to the entropy length.
 * \param p_entropy     The entropy context to pass to \p f_entropy.
 * \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.
 *                      This must be at most #MBEDTLS_HMAC_DRBG_MAX_INPUT
 *                      and also at most
 *                      #MBEDTLS_HMAC_DRBG_MAX_SEED_INPUT - \p entropy_len * 3 / 2
 *                      where \p entropy_len is the entropy length
 *                      described above.
 *
 * \return              \c 0 if successful.
 * \return              #MBEDTLS_ERR_MD_BAD_INPUT_DATA if \p md_info is
 *                      invalid.
 * \return              #MBEDTLS_ERR_MD_ALLOC_FAILED if there was not enough
 *                      memory to allocate context data.
 * \return              #MBEDTLS_ERR_HMAC_DRBG_ENTROPY_SOURCE_FAILED
 *                      if the call to \p f_entropy failed.
 */
int mbedtls_hmac_drbg_seed(mbedtls_hmac_drbg_context *ctx,
                           const mbedtls_md_info_t *md_info,
                           int (*f_entropy)(void *, unsigned char *, size_t),
                           void *p_entropy,
                           const unsigned char *custom,
                           size_t len);

/**
 * \brief               Initilisation of simpified HMAC_DRBG (never reseeds).
 *
 * This function is meant for use in algorithms that need a pseudorandom
 * input such as deterministic ECDSA.
 */
#if defined(MBEDTLS_THREADING_C)
/**
 * \note                When Mbed TLS is built with threading support,
 *                      after this function returns successfully,
 *                      it is safe to call mbedtls_hmac_drbg_random()
 *                      from multiple threads. Other operations, including
 *                      reseeding, are not thread-safe.
 */
#endif /* MBEDTLS_THREADING_C */
/**
 * \param ctx           HMAC_DRBG context to be initialised.
 * \param md_info       MD algorithm to use for HMAC_DRBG.
 * \param data          Concatenation of the initial entropy string and
 *                      the additional data.
 * \param data_len      Length of \p data in bytes.
 *
 * \return              \c 0 if successful. or
 * \return              #MBEDTLS_ERR_MD_BAD_INPUT_DATA if \p md_info is
 *                      invalid.
 * \return              #MBEDTLS_ERR_MD_ALLOC_FAILED if there was not enough
 *                      memory to allocate context data.
 */
int mbedtls_hmac_drbg_seed_buf(mbedtls_hmac_drbg_context *ctx,
                               const mbedtls_md_info_t *md_info,
                               const unsigned char *data,
                               size_t data_len);

/**
 * \brief               This function turns prediction resistance on or off.
 *                      The default value is off.
 *
 * \note                If enabled, entropy is gathered at the beginning of
 *                      every call to mbedtls_hmac_drbg_random_with_add()
 *                      or mbedtls_hmac_drbg_random().
 *                      Only use this if your entropy source has sufficient
 *                      throughput.
 *
 * \param ctx           The HMAC_DRBG context.
 * \param resistance    #MBEDTLS_HMAC_DRBG_PR_ON or #MBEDTLS_HMAC_DRBG_PR_OFF.
 */
void mbedtls_hmac_drbg_set_prediction_resistance(mbedtls_hmac_drbg_context *ctx,
                                                 int resistance);

/**
 * \brief               This function sets the amount of entropy grabbed on each
 *                      seed or reseed.
 *
 * See the documentation of mbedtls_hmac_drbg_seed() for the default value.
 *
 * \param ctx           The HMAC_DRBG context.
 * \param len           The amount of entropy to grab, in bytes.
 */
void mbedtls_hmac_drbg_set_entropy_len(mbedtls_hmac_drbg_context *ctx,
                                       size_t len);

/**
 * \brief               Set the reseed interval.
 *
 * The reseed interval is the number of calls to mbedtls_hmac_drbg_random()
 * or mbedtls_hmac_drbg_random_with_add() after which the entropy function
 * is called again.
 *
 * The default value is #MBEDTLS_HMAC_DRBG_RESEED_INTERVAL.
 *
 * \param ctx           The HMAC_DRBG context.
 * \param interval      The reseed interval.
 */
void mbedtls_hmac_drbg_set_reseed_interval(mbedtls_hmac_drbg_context *ctx,
                                           int interval);

/**
 * \brief               This function updates the state of the HMAC_DRBG context.
 *
 * \note                This function is not thread-safe. It is not safe
 *                      to call this function if another thread might be
 *                      concurrently obtaining random numbers from the same
 *                      context or updating or reseeding the same context.
 *
 * \param ctx           The HMAC_DRBG context.
 * \param additional    The data to update the state with.
 *                      If this is \c NULL, there is no additional data.
 * \param add_len       Length of \p additional in bytes.
 *                      Unused if \p additional is \c NULL.
 *
 * \return              \c 0 on success, or an error from the underlying
 *                      hash calculation.
 */
int mbedtls_hmac_drbg_update(mbedtls_hmac_drbg_context *ctx,
                             const unsigned char *additional,
                             size_t add_len);

/**
 * \brief               This function reseeds the HMAC_DRBG context, that is
 *                      extracts data from the entropy source.
 *
 * \note                This function is not thread-safe. It is not safe
 *                      to call this function if another thread might be
 *                      concurrently obtaining random numbers from the same
 *                      context or updating or reseeding the same context.
 *
 * \param ctx           The HMAC_DRBG context.
 * \param additional    Additional data to add to the state.
 *                      If this is \c NULL, there is no additional data
 *                      and \p len should be \c 0.
 * \param len           The length of the additional data.
 *                      This must be at most #MBEDTLS_HMAC_DRBG_MAX_INPUT
 *                      and also at most
 *                      #MBEDTLS_HMAC_DRBG_MAX_SEED_INPUT - \p entropy_len
 *                      where \p entropy_len is the entropy length
 *                      (see mbedtls_hmac_drbg_set_entropy_len()).
 *
 * \return              \c 0 if successful.
 * \return              #MBEDTLS_ERR_HMAC_DRBG_ENTROPY_SOURCE_FAILED
 *                      if a call to the entropy function failed.
 */
int mbedtls_hmac_drbg_reseed(mbedtls_hmac_drbg_context *ctx,
                             const unsigned char *additional,
                             size_t len);

/**
 * \brief   This function updates an HMAC_DRBG instance with additional
 *          data and uses it to generate random data.
 *
 * This function automatically reseeds if the reseed counter is exceeded
 * or prediction resistance is enabled.
 *
 * \note                This function is not thread-safe. It is not safe
 *                      to call this function if another thread might be
 *                      concurrently obtaining random numbers from the same
 *                      context or updating or reseeding the same context.
 *
 * \param p_rng         The HMAC_DRBG context. This must be a pointer to a
 *                      #mbedtls_hmac_drbg_context structure.
 * \param output        The buffer to fill.
 * \param output_len    The length of the buffer in bytes.
 *                      This must be at most #MBEDTLS_HMAC_DRBG_MAX_REQUEST.
 * \param additional    Additional data to update with.
 *                      If this is \c NULL, there is no additional data
 *                      and \p add_len should be \c 0.
 * \param add_len       The length of the additional data.
 *                      This must be at most #MBEDTLS_HMAC_DRBG_MAX_INPUT.
 *
 * \return              \c 0 if successful.
 * \return              #MBEDTLS_ERR_HMAC_DRBG_ENTROPY_SOURCE_FAILED
 *                      if a call to the entropy source failed.
 * \return              #MBEDTLS_ERR_HMAC_DRBG_REQUEST_TOO_BIG if
 *                      \p output_len > #MBEDTLS_HMAC_DRBG_MAX_REQUEST.
 * \return              #MBEDTLS_ERR_HMAC_DRBG_INPUT_TOO_BIG if
 *                      \p add_len > #MBEDTLS_HMAC_DRBG_MAX_INPUT.
 */
int mbedtls_hmac_drbg_random_with_add(void *p_rng,
                                      unsigned char *output,
                                      size_t output_len,
                                      const unsigned char *additional,
                                      size_t add_len);

/**
 * \brief   This function uses HMAC_DRBG to generate random data.
 *
 * This function automatically reseeds if the reseed counter is exceeded
 * or prediction resistance is enabled.
 */
#if defined(MBEDTLS_THREADING_C)
/**
 * \note                When Mbed TLS is built with threading support,
 *                      it is safe to call mbedtls_ctr_drbg_random()
 *                      from multiple threads. Other operations, including
 *                      reseeding, are not thread-safe.
 */
#endif /* MBEDTLS_THREADING_C */
/**
 * \param p_rng         The HMAC_DRBG context. This must be a pointer to a
 *                      #mbedtls_hmac_drbg_context structure.
 * \param output        The buffer to fill.
 * \param out_len       The length of the buffer in bytes.
 *                      This must be at most #MBEDTLS_HMAC_DRBG_MAX_REQUEST.
 *
 * \return              \c 0 if successful.
 * \return              #MBEDTLS_ERR_HMAC_DRBG_ENTROPY_SOURCE_FAILED
 *                      if a call to the entropy source failed.
 * \return              #MBEDTLS_ERR_HMAC_DRBG_REQUEST_TOO_BIG if
 *                      \p out_len > #MBEDTLS_HMAC_DRBG_MAX_REQUEST.
 */
int mbedtls_hmac_drbg_random(void *p_rng,
                             unsigned char *output,
                             size_t out_len);

/**
 * \brief               This function resets HMAC_DRBG context to the state immediately
 *                      after initial call of mbedtls_hmac_drbg_init().
 *
 * \param ctx           The HMAC_DRBG context to free.
 */
void mbedtls_hmac_drbg_free(mbedtls_hmac_drbg_context *ctx);

#if defined(MBEDTLS_FS_IO)
/**
 * \brief               This function writes a seed file.
 *
 * \param ctx           The HMAC_DRBG context.
 * \param path          The name of the file.
 *
 * \return              \c 0 on success.
 * \return              #MBEDTLS_ERR_HMAC_DRBG_FILE_IO_ERROR on file error.
 * \return              #MBEDTLS_ERR_HMAC_DRBG_ENTROPY_SOURCE_FAILED on reseed
 *                      failure.
 */
int mbedtls_hmac_drbg_write_seed_file(mbedtls_hmac_drbg_context *ctx,
                                      const char *path);

/**
 * \brief               This function reads and updates a seed file. The seed
 *                      is added to this instance.
 *
 * \param ctx           The HMAC_DRBG context.
 * \param path          The name of the file.
 *
 * \return              \c 0 on success.
 * \return              #MBEDTLS_ERR_HMAC_DRBG_FILE_IO_ERROR on file error.
 * \return              #MBEDTLS_ERR_HMAC_DRBG_ENTROPY_SOURCE_FAILED on
 *                      reseed failure.
 * \return              #MBEDTLS_ERR_HMAC_DRBG_INPUT_TOO_BIG if the existing
 *                      seed file is too large.
 */
int mbedtls_hmac_drbg_update_seed_file(mbedtls_hmac_drbg_context *ctx,
                                       const char *path);
#endif /* MBEDTLS_FS_IO */

#if defined(MBEDTLS_SELF_TEST)
/**
 * \brief               The HMAC_DRBG Checkup routine.
 *
 * \return              \c 0 if successful.
 * \return              \c 1 if the test failed.
 */
int mbedtls_hmac_drbg_self_test(int verbose);
#endif

#ifdef __cplusplus
}
#endif

#endif /* hmac_drbg.h */