text: /**
   * \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)
  #define MBEDTLS_HMAC_DRBG_RESEED_INTERVAL   10000   /**< Interval before reseed is performed by default */
  #endif
  
  #if !defined(MBEDTLS_HMAC_DRBG_MAX_INPUT)
  #define MBEDTLS_HMAC_DRBG_MAX_INPUT         256     /**< Maximum number of additional input bytes */
  #endif
  
  #if !defined(MBEDTLS_HMAC_DRBG_MAX_REQUEST)
  #define MBEDTLS_HMAC_DRBG_MAX_REQUEST       1024    /**< Maximum number of requested bytes per call */
  #endif
  
  #if !defined(MBEDTLS_HMAC_DRBG_MAX_SEED_INPUT)
  #define MBEDTLS_HMAC_DRBG_MAX_SEED_INPUT    384     /**< Maximum size of (re)seed buffer */
  #endif
  
  /* \} name SECTION: Module settings */
  
  #define MBEDTLS_HMAC_DRBG_PR_OFF   0   /**< No prediction resistance       */
  #define MBEDTLS_HMAC_DRBG_PR_ON    1   /**< Prediction resistance enabled  */
  
  #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 */
  