text: /**
   * \file cipher.h
   *
   * \brief This file contains an abstraction interface for use with the cipher
   * primitives provided by the library. It provides a common interface to all of
   * the available cipher operations.
   *
   * \author Adriaan de Jong <dejong@fox-it.com>
   */
  /*
   *  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_CIPHER_H
  #define MBEDTLS_CIPHER_H
  #include "private_access.h"
  
  #if !defined(MBEDTLS_CONFIG_FILE)
  #include "config.h"
  #else
  #include MBEDTLS_CONFIG_FILE
  #endif
  
  #include <stddef.h>
  #include "platform_util.h"
  
  #if defined(MBEDTLS_GCM_C) || defined(MBEDTLS_CCM_C) || defined(MBEDTLS_CHACHAPOLY_C)
  #define MBEDTLS_CIPHER_MODE_AEAD
  #endif
  
  #if defined(MBEDTLS_CIPHER_MODE_CBC)
  #define MBEDTLS_CIPHER_MODE_WITH_PADDING
  #endif
  
  #if defined(MBEDTLS_ARC4_C) || defined(MBEDTLS_CIPHER_NULL_CIPHER) || \
      defined(MBEDTLS_CHACHA20_C)
  #define MBEDTLS_CIPHER_MODE_STREAM
  #endif
  
  #if ( defined(__ARMCC_VERSION) || defined(_MSC_VER) ) && \
      !defined(inline) && !defined(__cplusplus)
  #define inline __inline
  #endif
  
  #define MBEDTLS_ERR_CIPHER_FEATURE_UNAVAILABLE  -0x6080  /**< The selected feature is not available. */
  #define MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA       -0x6100  /**< Bad input parameters. */
  #define MBEDTLS_ERR_CIPHER_ALLOC_FAILED         -0x6180  /**< Failed to allocate memory. */
  #define MBEDTLS_ERR_CIPHER_INVALID_PADDING      -0x6200  /**< Input data contains invalid padding and is rejected. */
  #define MBEDTLS_ERR_CIPHER_FULL_BLOCK_EXPECTED  -0x6280  /**< Decryption of block requires a full block. */
  #define MBEDTLS_ERR_CIPHER_AUTH_FAILED          -0x6300  /**< Authentication failed (for AEAD modes). */
  #define MBEDTLS_ERR_CIPHER_INVALID_CONTEXT      -0x6380  /**< The context is invalid. For example, because it was freed. */
  
  #define MBEDTLS_CIPHER_VARIABLE_IV_LEN     0x01    /**< Cipher accepts IVs of variable length. */
  #define MBEDTLS_CIPHER_VARIABLE_KEY_LEN    0x02    /**< Cipher accepts keys of variable length. */
  
  #ifdef __cplusplus
  extern "C" {
  #endif
  
  /**
   * \brief     Supported cipher types.
   *
   * \warning   RC4 and DES are considered weak ciphers and their use
   *            constitutes a security risk. Arm recommends considering stronger
   *            ciphers instead.
   */
  typedef enum {
      MBEDTLS_CIPHER_ID_NONE = 0,  /**< Placeholder to mark the end of cipher ID lists. */
      MBEDTLS_CIPHER_ID_NULL,      /**< The identity cipher, treated as a stream cipher. */
      MBEDTLS_CIPHER_ID_AES,       /**< The AES cipher. */
      MBEDTLS_CIPHER_ID_DES,       /**< The DES cipher. */
      MBEDTLS_CIPHER_ID_3DES,      /**< The Triple DES cipher. */
      MBEDTLS_CIPHER_ID_CAMELLIA,  /**< The Camellia cipher. */
      MBEDTLS_CIPHER_ID_BLOWFISH,  /**< The Blowfish cipher. */
      MBEDTLS_CIPHER_ID_ARC4,      /**< The RC4 cipher. */
      MBEDTLS_CIPHER_ID_ARIA,      /**< The Aria cipher. */
      MBEDTLS_CIPHER_ID_CHACHA20,  /**< The ChaCha20 cipher. */
  } mbedtls_cipher_id_t;
  
  /**
   * \brief     Supported {cipher type, cipher mode} pairs.
   *
   * \warning   RC4 and DES are considered weak ciphers and their use
   *            constitutes a security risk. Arm recommends considering stronger
   *            ciphers instead.
   */
  typedef enum {
      MBEDTLS_CIPHER_NONE = 0,             /**< Placeholder to mark the end of cipher-pair lists. */
      MBEDTLS_CIPHER_NULL,                 /**< The identity stream cipher. */
      MBEDTLS_CIPHER_AES_128_ECB,          /**< AES cipher with 128-bit ECB mode. */
      MBEDTLS_CIPHER_AES_192_ECB,          /**< AES cipher with 192-bit ECB mode. */
      MBEDTLS_CIPHER_AES_256_ECB,          /**< AES cipher with 256-bit ECB mode. */
      MBEDTLS_CIPHER_AES_128_CBC,          /**< AES cipher with 128-bit CBC mode. */
      MBEDTLS_CIPHER_AES_192_CBC,          /**< AES cipher with 192-bit CBC mode. */
      MBEDTLS_CIPHER_AES_256_CBC,          /**< AES cipher with 256-bit CBC mode. */
      MBEDTLS_CIPHER_AES_128_CFB128,       /**< AES cipher with 128-bit CFB128 mode. */
      MBEDTLS_CIPHER_AES_192_CFB128,       /**< AES cipher with 192-bit CFB128 mode. */
      MBEDTLS_CIPHER_AES_256_CFB128,       /**< AES cipher with 256-bit CFB128 mode. */
      MBEDTLS_CIPHER_AES_128_CTR,          /**< AES cipher with 128-bit CTR mode. */
      MBEDTLS_CIPHER_AES_192_CTR,          /**< AES cipher with 192-bit CTR mode. */
      MBEDTLS_CIPHER_AES_256_CTR,          /**< AES cipher with 256-bit CTR mode. */
      MBEDTLS_CIPHER_AES_128_GCM,          /**< AES cipher with 128-bit GCM mode. */
      MBEDTLS_CIPHER_AES_192_GCM,          /**< AES cipher with 192-bit GCM mode. */
      MBEDTLS_CIPHER_AES_256_GCM,          /**< AES cipher with 256-bit GCM mode. */
      MBEDTLS_CIPHER_CAMELLIA_128_ECB,     /**< Camellia cipher with 128-bit ECB mode. */
      MBEDTLS_CIPHER_CAMELLIA_192_ECB,     /**< Camellia cipher with 192-bit ECB mode. */
      MBEDTLS_CIPHER_CAMELLIA_256_ECB,     /**< Camellia cipher with 256-bit ECB mode. */
      MBEDTLS_CIPHER_CAMELLIA_128_CBC,     /**< Camellia cipher with 128-bit CBC mode. */
      MBEDTLS_CIPHER_CAMELLIA_192_CBC,     /**< Camellia cipher with 192-bit CBC mode. */
      MBEDTLS_CIPHER_CAMELLIA_256_CBC,     /**< Camellia cipher with 256-bit CBC mode. */
      MBEDTLS_CIPHER_CAMELLIA_128_CFB128,  /**< Camellia cipher with 128-bit CFB128 mode. */
      MBEDTLS_CIPHER_CAMELLIA_192_CFB128,  /**< Camellia cipher with 192-bit CFB128 mode. */
      MBEDTLS_CIPHER_CAMELLIA_256_CFB128,  /**< Camellia cipher with 256-bit CFB128 mode. */
      MBEDTLS_CIPHER_CAMELLIA_128_CTR,     /**< Camellia cipher with 128-bit CTR mode. */
      MBEDTLS_CIPHER_CAMELLIA_192_CTR,     /**< Camellia cipher with 192-bit CTR mode. */
      MBEDTLS_CIPHER_CAMELLIA_256_CTR,     /**< Camellia cipher with 256-bit CTR mode. */
      MBEDTLS_CIPHER_CAMELLIA_128_GCM,     /**< Camellia cipher with 128-bit GCM mode. */
      MBEDTLS_CIPHER_CAMELLIA_192_GCM,     /**< Camellia cipher with 192-bit GCM mode. */
      MBEDTLS_CIPHER_CAMELLIA_256_GCM,     /**< Camellia cipher with 256-bit GCM mode. */
      MBEDTLS_CIPHER_DES_ECB,              /**< DES cipher with ECB mode. */
      MBEDTLS_CIPHER_DES_CBC,              /**< DES cipher with CBC mode. */
      MBEDTLS_CIPHER_DES_EDE_ECB,          /**< DES cipher with EDE ECB mode. */
      MBEDTLS_CIPHER_DES_EDE_CBC,          /**< DES cipher with EDE CBC mode. */
      MBEDTLS_CIPHER_DES_EDE3_ECB,         /**< DES cipher with EDE3 ECB mode. */
      MBEDTLS_CIPHER_DES_EDE3_CBC,         /**< DES cipher with EDE3 CBC mode. */
      MBEDTLS_CIPHER_BLOWFISH_ECB,         /**< Blowfish cipher with ECB mode. */
      MBEDTLS_CIPHER_BLOWFISH_CBC,         /**< Blowfish cipher with CBC mode. */
      MBEDTLS_CIPHER_BLOWFISH_CFB64,       /**< Blowfish cipher with CFB64 mode. */
      MBEDTLS_CIPHER_BLOWFISH_CTR,         /**< Blowfish cipher with CTR mode. */
      MBEDTLS_CIPHER_ARC4_128,             /**< RC4 cipher with 128-bit mode. */
      MBEDTLS_CIPHER_AES_128_CCM,          /**< AES cipher with 128-bit CCM mode. */
      MBEDTLS_CIPHER_AES_192_CCM,          /**< AES cipher with 192-bit CCM mode. */
      MBEDTLS_CIPHER_AES_256_CCM,          /**< AES cipher with 256-bit CCM mode. */
      MBEDTLS_CIPHER_CAMELLIA_128_CCM,     /**< Camellia cipher with 128-bit CCM mode. */
      MBEDTLS_CIPHER_CAMELLIA_192_CCM,     /**< Camellia cipher with 192-bit CCM mode. */
      MBEDTLS_CIPHER_CAMELLIA_256_CCM,     /**< Camellia cipher with 256-bit CCM mode. */
      MBEDTLS_CIPHER_ARIA_128_ECB,         /**< Aria cipher with 128-bit key and ECB mode. */
      MBEDTLS_CIPHER_ARIA_192_ECB,         /**< Aria cipher with 192-bit key and ECB mode. */
      MBEDTLS_CIPHER_ARIA_256_ECB,         /**< Aria cipher with 256-bit key and ECB mode. */
      MBEDTLS_CIPHER_ARIA_128_CBC,         /**< Aria cipher with 128-bit key and CBC mode. */
      MBEDTLS_CIPHER_ARIA_192_CBC,         /**< Aria cipher with 192-bit key and CBC mode. */
      MBEDTLS_CIPHER_ARIA_256_CBC,         /**< Aria cipher with 256-bit key and CBC mode. */
      MBEDTLS_CIPHER_ARIA_128_CFB128,      /**< Aria cipher with 128-bit key and CFB-128 mode. */
      MBEDTLS_CIPHER_ARIA_192_CFB128,      /**< Aria cipher with 192-bit key and CFB-128 mode. */
      MBEDTLS_CIPHER_ARIA_256_CFB128,      /**< Aria cipher with 256-bit key and CFB-128 mode. */
      MBEDTLS_CIPHER_ARIA_128_CTR,         /**< Aria cipher with 128-bit key and CTR mode. */
      MBEDTLS_CIPHER_ARIA_192_CTR,         /**< Aria cipher with 192-bit key and CTR mode. */
      MBEDTLS_CIPHER_ARIA_256_CTR,         /**< Aria cipher with 256-bit key and CTR mode. */
      MBEDTLS_CIPHER_ARIA_128_GCM,         /**< Aria cipher with 128-bit key and GCM mode. */
      MBEDTLS_CIPHER_ARIA_192_GCM,         /**< Aria cipher with 192-bit key and GCM mode. */
      MBEDTLS_CIPHER_ARIA_256_GCM,         /**< Aria cipher with 256-bit key and GCM mode. */
      MBEDTLS_CIPHER_ARIA_128_CCM,         /**< Aria cipher with 128-bit key and CCM mode. */
      MBEDTLS_CIPHER_ARIA_192_CCM,         /**< Aria cipher with 192-bit key and CCM mode. */
      MBEDTLS_CIPHER_ARIA_256_CCM,         /**< Aria cipher with 256-bit key and CCM mode. */
      MBEDTLS_CIPHER_AES_128_OFB,          /**< AES 128-bit cipher in OFB mode. */
      MBEDTLS_CIPHER_AES_192_OFB,          /**< AES 192-bit cipher in OFB mode. */
      MBEDTLS_CIPHER_AES_256_OFB,          /**< AES 256-bit cipher in OFB mode. */
      MBEDTLS_CIPHER_AES_128_XTS,          /**< AES 128-bit cipher in XTS block mode. */
      MBEDTLS_CIPHER_AES_256_XTS,          /**< AES 256-bit cipher in XTS block mode. */
      MBEDTLS_CIPHER_CHACHA20,             /**< ChaCha20 stream cipher. */
      MBEDTLS_CIPHER_CHACHA20_POLY1305,    /**< ChaCha20-Poly1305 AEAD cipher. */
      MBEDTLS_CIPHER_AES_128_KW,           /**< AES cipher with 128-bit NIST KW mode. */
      MBEDTLS_CIPHER_AES_192_KW,           /**< AES cipher with 192-bit NIST KW mode. */
      MBEDTLS_CIPHER_AES_256_KW,           /**< AES cipher with 256-bit NIST KW mode. */
      MBEDTLS_CIPHER_AES_128_KWP,          /**< AES cipher with 128-bit NIST KWP mode. */
      MBEDTLS_CIPHER_AES_192_KWP,          /**< AES cipher with 192-bit NIST KWP mode. */
      MBEDTLS_CIPHER_AES_256_KWP,          /**< AES cipher with 256-bit NIST KWP mode. */
  } mbedtls_cipher_type_t;
  
  /** Supported cipher modes. */
  typedef enum {
      MBEDTLS_MODE_NONE = 0,               /**< None.                        */
      MBEDTLS_MODE_ECB,                    /**< The ECB cipher mode.         */
      MBEDTLS_MODE_CBC,                    /**< The CBC cipher mode.         */
      MBEDTLS_MODE_CFB,                    /**< The CFB cipher mode.         */
      MBEDTLS_MODE_OFB,                    /**< The OFB cipher mode.         */
      MBEDTLS_MODE_CTR,                    /**< The CTR cipher mode.         */
      MBEDTLS_MODE_GCM,                    /**< The GCM cipher mode.         */
      MBEDTLS_MODE_STREAM,                 /**< The stream cipher mode.      */
      MBEDTLS_MODE_CCM,                    /**< The CCM cipher mode.         */
      MBEDTLS_MODE_XTS,                    /**< The XTS cipher mode.         */
      MBEDTLS_MODE_CHACHAPOLY,             /**< The ChaCha-Poly cipher mode. */
      MBEDTLS_MODE_KW,                     /**< The SP800-38F KW mode */
      MBEDTLS_MODE_KWP,                    /**< The SP800-38F KWP mode */
  } mbedtls_cipher_mode_t;
  
  /** Supported cipher padding types. */
  typedef enum {
      MBEDTLS_PADDING_PKCS7 = 0,     /**< PKCS7 padding (default).        */
      MBEDTLS_PADDING_ONE_AND_ZEROS, /**< ISO/IEC 7816-4 padding.         */
      MBEDTLS_PADDING_ZEROS_AND_LEN, /**< ANSI X.923 padding.             */
      MBEDTLS_PADDING_ZEROS,         /**< Zero padding (not reversible). */
      MBEDTLS_PADDING_NONE,          /**< Never pad (full blocks only).   */
  } mbedtls_cipher_padding_t;
  
  /** Type of operation. */
  typedef enum {
      MBEDTLS_OPERATION_NONE = -1,
      MBEDTLS_DECRYPT = 0,
      MBEDTLS_ENCRYPT,
  } mbedtls_operation_t;
  
  enum {
      /** Undefined key length. */
      MBEDTLS_KEY_LENGTH_NONE = 0,
      /** Key length, in bits (including parity), for DES keys. */
      MBEDTLS_KEY_LENGTH_DES  = 64,
      /** Key length in bits, including parity, for DES in two-key EDE. */
      MBEDTLS_KEY_LENGTH_DES_EDE = 128,
      /** Key length in bits, including parity, for DES in three-key EDE. */
      MBEDTLS_KEY_LENGTH_DES_EDE3 = 192,
  };
  
  /** Maximum length of any IV, in Bytes. */
  /* This should ideally be derived automatically from list of ciphers.
   * This should be kept in sync with MBEDTLS_SSL_MAX_IV_LENGTH defined
   * in library/ssl_misc.h. */
  #define MBEDTLS_MAX_IV_LENGTH      16
  
  /** Maximum block size of any cipher, in Bytes. */
  /* This should ideally be derived automatically from list of ciphers.
   * This should be kept in sync with MBEDTLS_SSL_MAX_BLOCK_LENGTH defined
   * in library/ssl_misc.h. */
  #define MBEDTLS_MAX_BLOCK_LENGTH   16
  
  /** Maximum key length, in Bytes. */
  /* This should ideally be derived automatically from list of ciphers.
   * For now, only check whether XTS is enabled which uses 64 Byte keys,
   * and use 32 Bytes as an upper bound for the maximum key length otherwise.
   * This should be kept in sync with MBEDTLS_SSL_MAX_BLOCK_LENGTH defined
   * in library/ssl_misc.h, which however deliberately ignores the case of XTS
   * since the latter isn't used in SSL/TLS. */
  #if defined(MBEDTLS_CIPHER_MODE_XTS)
  #define MBEDTLS_MAX_KEY_LENGTH     64
  #else
  #define MBEDTLS_MAX_KEY_LENGTH     32
  #endif /* MBEDTLS_CIPHER_MODE_XTS */
  
  /**
   * Base cipher information (opaque struct).
   */
  typedef struct mbedtls_cipher_base_t mbedtls_cipher_base_t;
  
  /**
   * CMAC context (opaque struct).
   */
  typedef struct mbedtls_cmac_context_t mbedtls_cmac_context_t;
  
  /**
   * Cipher information. Allows calling cipher functions
   * in a generic way.
   */
  typedef struct mbedtls_cipher_info_t
  {
      /** Full cipher identifier. For example,
       * MBEDTLS_CIPHER_AES_256_CBC.
       */
      mbedtls_cipher_type_t MBEDTLS_PRIVATE(type);
  
      /** The cipher mode. For example, MBEDTLS_MODE_CBC. */
      mbedtls_cipher_mode_t MBEDTLS_PRIVATE(mode);
  
      /** The cipher key length, in bits. This is the
       * default length for variable sized ciphers.
       * Includes parity bits for ciphers like DES.
       */
      unsigned int MBEDTLS_PRIVATE(key_bitlen);
  
      /** Name of the cipher. */
      const char * MBEDTLS_PRIVATE(name);
  
      /** IV or nonce size, in Bytes.
       * For ciphers that accept variable IV sizes,
       * this is the recommended size.
       */
      unsigned int MBEDTLS_PRIVATE(iv_size);
  
      /** Bitflag comprised of MBEDTLS_CIPHER_VARIABLE_IV_LEN and
       *  MBEDTLS_CIPHER_VARIABLE_KEY_LEN indicating whether the
       *  cipher supports variable IV or variable key sizes, respectively.
       */
      int MBEDTLS_PRIVATE(flags);
  
      /** The block size, in Bytes. */
      unsigned int MBEDTLS_PRIVATE(block_size);
  
      /** Struct for base cipher information and functions. */
      const mbedtls_cipher_base_t *MBEDTLS_PRIVATE(base);
  
  } mbedtls_cipher_info_t;
  
  /**
   * Generic cipher context.
   */
  typedef struct mbedtls_cipher_context_t
  {
      /** Information about the associated cipher. */
      const mbedtls_cipher_info_t *MBEDTLS_PRIVATE(cipher_info);
  
      /** Key length to use. */
      int MBEDTLS_PRIVATE(key_bitlen);
  
      /** Operation that the key of the context has been
       * initialized for.
       */
      mbedtls_operation_t MBEDTLS_PRIVATE(operation);
  
  #if defined(MBEDTLS_CIPHER_MODE_WITH_PADDING)
      /** Padding functions to use, if relevant for
       * the specific cipher mode.
       */
      void (*MBEDTLS_PRIVATE(add_padding))( unsigned char *output, size_t olen, size_t data_len );
      int (*MBEDTLS_PRIVATE(get_padding))( unsigned char *input, size_t ilen, size_t *data_len );
  #endif
  
      /** Buffer for input that has not been processed yet. */
      unsigned char MBEDTLS_PRIVATE(unprocessed_data)[MBEDTLS_MAX_BLOCK_LENGTH];
  
      /** Number of Bytes that have not been processed yet. */
      size_t MBEDTLS_PRIVATE(unprocessed_len);
  
      /** Current IV or NONCE_COUNTER for CTR-mode, data unit (or sector) number
       * for XTS-mode. */
      unsigned char MBEDTLS_PRIVATE(iv)[MBEDTLS_MAX_IV_LENGTH];
  
      /** IV size in Bytes, for ciphers with variable-length IVs. */
      size_t MBEDTLS_PRIVATE(iv_size);
  
      /** The cipher-specific context. */
      void *MBEDTLS_PRIVATE(cipher_ctx);
  
  #if defined(MBEDTLS_CMAC_C)
      /** CMAC-specific context. */
      mbedtls_cmac_context_t *MBEDTLS_PRIVATE(cmac_ctx);
  #endif
  
  #if defined(MBEDTLS_USE_PSA_CRYPTO)
      /** Indicates whether the cipher operations should be performed
       *  by Mbed TLS' own crypto library or an external implementation
       *  of the PSA Crypto API.
       *  This is unset if the cipher context was established through
       *  mbedtls_cipher_setup(), and set if it was established through
       *  mbedtls_cipher_setup_psa().
       */
      unsigned char MBEDTLS_PRIVATE(psa_enabled);
  #endif /* MBEDTLS_USE_PSA_CRYPTO */
  
  } mbedtls_cipher_context_t;
  
  /**
   * \brief This function retrieves the list of ciphers supported
   *        by the generic cipher module.
   *
   *        For any cipher identifier in the returned list, you can
   *        obtain the corresponding generic cipher information structure
   *        via mbedtls_cipher_info_from_type(), which can then be used
   *        to prepare a cipher context via mbedtls_cipher_setup().
   *
   *
   * \return      A statically-allocated array of cipher identifiers
   *              of type cipher_type_t. The last entry is zero.
   */
  const int *mbedtls_cipher_list( void );
  
  /**
   * \brief               This function retrieves the cipher-information
   *                      structure associated with the given cipher name.
   *
   * \param cipher_name   Name of the cipher to search for. This must not be
   *                      \c NULL.
   *
   * \return              The cipher information structure associated with the
   *                      given \p cipher_name.
   * \return              \c NULL if the associated cipher information is not found.
   */
  const mbedtls_cipher_info_t *mbedtls_cipher_info_from_string( const char *cipher_name );
  
  /**
   * \brief               This function retrieves the cipher-information
   *                      structure associated with the given cipher type.
   *
   * \param cipher_type   Type of the cipher to search for.
   *
   * \return              The cipher information structure associated with the
   *                      given \p cipher_type.
   * \return              \c NULL if the associated cipher information is not found.
   */
  const mbedtls_cipher_info_t *mbedtls_cipher_info_from_type( const mbedtls_cipher_type_t cipher_type );
  
  /**
   * \brief               This function retrieves the cipher-information
   *                      structure associated with the given cipher ID,
   *                      key size and mode.
   *
   * \param cipher_id     The ID of the cipher to search for. For example,
   *                      #MBEDTLS_CIPHER_ID_AES.
   * \param key_bitlen    The length of the key in bits.
   * \param mode          The cipher mode. For example, #MBEDTLS_MODE_CBC.
   *
   * \return              The cipher information structure associated with the
   *                      given \p cipher_id.
   * \return              \c NULL if the associated cipher information is not found.
   */
  const mbedtls_cipher_info_t *mbedtls_cipher_info_from_values( const mbedtls_cipher_id_t cipher_id,
                                                int key_bitlen,
                                                const mbedtls_cipher_mode_t mode );
  
  /**
   * \brief               This function initializes a \p cipher_context as NONE.
   *
   * \param ctx           The context to be initialized. This must not be \c NULL.
   */
  void mbedtls_cipher_init( mbedtls_cipher_context_t *ctx );
  
  /**
   * \brief               This function frees and clears the cipher-specific
   *                      context of \p ctx. Freeing \p ctx itself remains the
   *                      responsibility of the caller.
   *
   * \param ctx           The context to be freed. If this is \c NULL, the
   *                      function has no effect, otherwise this must point to an
   *                      initialized context.
   */
  void mbedtls_cipher_free( mbedtls_cipher_context_t *ctx );
  
  
  /**
   * \brief               This function prepares a cipher context for
   *                      use with the given cipher primitive.
   *
   * \note                After calling this function, you should call
   *                      mbedtls_cipher_setkey() and, if the mode uses padding,
   *                      mbedtls_cipher_set_padding_mode(), then for each
   *                      message to encrypt or decrypt with this key, either:
   *                      - mbedtls_cipher_crypt() for one-shot processing with
   *                      non-AEAD modes;
   *                      - mbedtls_cipher_auth_encrypt_ext() or
   *                      mbedtls_cipher_auth_decrypt_ext() for one-shot
   *                      processing with AEAD modes or NIST_KW;
   *                      - for multi-part processing, see the documentation of
   *                      mbedtls_cipher_reset().
   *
   * \param ctx           The context to prepare. This must be initialized by
   *                      a call to mbedtls_cipher_init() first.
   * \param cipher_info   The cipher to use.
   *
   * \return              \c 0 on success.
   * \return              #MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA on
   *                      parameter-verification failure.
   * \return              #MBEDTLS_ERR_CIPHER_ALLOC_FAILED if allocation of the
   *                      cipher-specific context fails.
   */
  int mbedtls_cipher_setup( mbedtls_cipher_context_t *ctx,
                            const mbedtls_cipher_info_t *cipher_info );
  
  #if defined(MBEDTLS_USE_PSA_CRYPTO)
  /**
   * \brief               This function initializes a cipher context for
   *                      PSA-based use with the given cipher primitive.
   *
   * \note                See #MBEDTLS_USE_PSA_CRYPTO for information on PSA.
   *
   * \param ctx           The context to initialize. May not be \c NULL.
   * \param cipher_info   The cipher to use.
   * \param taglen        For AEAD ciphers, the length in bytes of the
   *                      authentication tag to use. Subsequent uses of
   *                      mbedtls_cipher_auth_encrypt_ext() or
   *                      mbedtls_cipher_auth_decrypt_ext() must provide
   *                      the same tag length.
   *                      For non-AEAD ciphers, the value must be \c 0.
   *
   * \return              \c 0 on success.
   * \return              #MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA on
   *                      parameter-verification failure.
   * \return              #MBEDTLS_ERR_CIPHER_ALLOC_FAILED if allocation of the
   *                      cipher-specific context fails.
   */
  int mbedtls_cipher_setup_psa( mbedtls_cipher_context_t *ctx,
                                const mbedtls_cipher_info_t *cipher_info,
                                size_t taglen );
  #endif /* MBEDTLS_USE_PSA_CRYPTO */
  
  /**
   * \brief        This function returns the block size of the given cipher.
   *
   * \param ctx    The context of the cipher. This must be initialized.
   *
   * \return       The block size of the underlying cipher.
   * \return       \c 0 if \p ctx has not been initialized.
   */
  static inline unsigned int mbedtls_cipher_get_block_size(
      const mbedtls_cipher_context_t *ctx )
  {
      MBEDTLS_INTERNAL_VALIDATE_RET( ctx != NULL, 0 );
      if( ctx->MBEDTLS_PRIVATE(cipher_info) == NULL )
          return 0;
  
      return ctx->MBEDTLS_PRIVATE(cipher_info)->MBEDTLS_PRIVATE(block_size);
  }
  
  /**
   * \brief        This function returns the mode of operation for
   *               the cipher. For example, MBEDTLS_MODE_CBC.
   *
   * \param ctx    The context of the cipher. This must be initialized.
   *
   * \return       The mode of operation.
   * \return       #MBEDTLS_MODE_NONE if \p ctx has not been initialized.
   */
  static inline mbedtls_cipher_mode_t mbedtls_cipher_get_cipher_mode(
      const mbedtls_cipher_context_t *ctx )
  {
      MBEDTLS_INTERNAL_VALIDATE_RET( ctx != NULL, MBEDTLS_MODE_NONE );
      if( ctx->MBEDTLS_PRIVATE(cipher_info) == NULL )
          return MBEDTLS_MODE_NONE;
  
      return ctx->MBEDTLS_PRIVATE(cipher_info)->MBEDTLS_PRIVATE(mode);
  }
  
  /**
   * \brief       This function returns the size of the IV or nonce
   *              of the cipher, in Bytes.
   *
   * \param ctx   The context of the cipher. This must be initialized.
   *
   * \return      The recommended IV size if no IV has been set.
   * \return      \c 0 for ciphers not using an IV or a nonce.
   * \return      The actual size if an IV has been set.
   */
  static inline int mbedtls_cipher_get_iv_size(
      const mbedtls_cipher_context_t *ctx )
  {
      MBEDTLS_INTERNAL_VALIDATE_RET( ctx != NULL, 0 );
      if( ctx->MBEDTLS_PRIVATE(cipher_info) == NULL )
          return 0;
  
      if( ctx->MBEDTLS_PRIVATE(iv_size) != 0 )
          return (int) ctx->MBEDTLS_PRIVATE(iv_size);
  
      return (int) ctx->MBEDTLS_PRIVATE(cipher_info)->MBEDTLS_PRIVATE(iv_size);
  }
  
  /**
   * \brief               This function returns the type of the given cipher.
   *
   * \param ctx           The context of the cipher. This must be initialized.
   *
   * \return              The type of the cipher.
   * \return              #MBEDTLS_CIPHER_NONE if \p ctx has not been initialized.
   */
  static inline mbedtls_cipher_type_t mbedtls_cipher_get_type(
      const mbedtls_cipher_context_t *ctx )
  {
      MBEDTLS_INTERNAL_VALIDATE_RET(
          ctx != NULL, MBEDTLS_CIPHER_NONE );
      if( ctx->MBEDTLS_PRIVATE(cipher_info) == NULL )
          return MBEDTLS_CIPHER_NONE;
  
      return ctx->MBEDTLS_PRIVATE(cipher_info)->MBEDTLS_PRIVATE(type);
  }
  
  /**
   * \brief               This function returns the name of the given cipher
   *                      as a string.
   *
   * \param ctx           The context of the cipher. This must be initialized.
   *
   * \return              The name of the cipher.
   * \return              NULL if \p ctx has not been not initialized.
   */
  static inline const char *mbedtls_cipher_get_name(
      const mbedtls_cipher_context_t *ctx )
  {
      MBEDTLS_INTERNAL_VALIDATE_RET( ctx != NULL, 0 );
      if( ctx->MBEDTLS_PRIVATE(cipher_info) == NULL )
          return 0;
  
      return ctx->MBEDTLS_PRIVATE(cipher_info)->MBEDTLS_PRIVATE(name);
  }
  
  /**
   * \brief               This function returns the key length of the cipher.
   *
   * \param ctx           The context of the cipher. This must be initialized.
   *
   * \return              The key length of the cipher in bits.
   * \return              #MBEDTLS_KEY_LENGTH_NONE if ctx \p has not been
   *                      initialized.
   */
  static inline int mbedtls_cipher_get_key_bitlen(
      const mbedtls_cipher_context_t *ctx )
  {
      MBEDTLS_INTERNAL_VALIDATE_RET(
          ctx != NULL, MBEDTLS_KEY_LENGTH_NONE );
      if( ctx->MBEDTLS_PRIVATE(cipher_info) == NULL )
          return MBEDTLS_KEY_LENGTH_NONE;
  
      return (int) ctx->MBEDTLS_PRIVATE(cipher_info)->MBEDTLS_PRIVATE(key_bitlen);
  }
  
  /**
   * \brief          This function returns the operation of the given cipher.
   *
   * \param ctx      The context of the cipher. This must be initialized.
   *
   * \return         The type of operation: #MBEDTLS_ENCRYPT or #MBEDTLS_DECRYPT.
   * \return         #MBEDTLS_OPERATION_NONE if \p ctx has not been initialized.
   */
  static inline mbedtls_operation_t mbedtls_cipher_get_operation(
      const mbedtls_cipher_context_t *ctx )
  {
      MBEDTLS_INTERNAL_VALIDATE_RET(
          ctx != NULL, MBEDTLS_OPERATION_NONE );
      if( ctx->MBEDTLS_PRIVATE(cipher_info) == NULL )
          return MBEDTLS_OPERATION_NONE;
  
      return ctx->MBEDTLS_PRIVATE(operation);
  }
  
  /**
   * \brief               This function sets the key to use with the given context.
   *
   * \param ctx           The generic cipher context. This must be initialized and
   *                      bound to a cipher information structure.
   * \param key           The key to use. This must be a readable buffer of at
   *                      least \p key_bitlen Bits.
   * \param key_bitlen    The key length to use, in Bits.
   * \param operation     The operation that the key will be used for:
   *                      #MBEDTLS_ENCRYPT or #MBEDTLS_DECRYPT.
   *
   * \return              \c 0 on success.
   * \return              #MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA on
   *                      parameter-verification failure.
   * \return              A cipher-specific error code on failure.
   */
  int mbedtls_cipher_setkey( mbedtls_cipher_context_t *ctx,
                             const unsigned char *key,
                             int key_bitlen,
                             const mbedtls_operation_t operation );
  
  #if defined(MBEDTLS_CIPHER_MODE_WITH_PADDING)
  /**
   * \brief               This function sets the padding mode, for cipher modes
   *                      that use padding.
   *
   *                      The default passing mode is PKCS7 padding.
   *
   * \param ctx           The generic cipher context. This must be initialized and
   *                      bound to a cipher information structure.
   * \param mode          The padding mode.
   *
   * \return              \c 0 on success.
   * \return              #MBEDTLS_ERR_CIPHER_FEATURE_UNAVAILABLE
   *                      if the selected padding mode is not supported.
   * \return              #MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA if the cipher mode
   *                      does not support padding.
   */
  int mbedtls_cipher_set_padding_mode( mbedtls_cipher_context_t *ctx,
                                       mbedtls_cipher_padding_t mode );
  #endif /* MBEDTLS_CIPHER_MODE_WITH_PADDING */
  
  /**
   * \brief           This function sets the initialization vector (IV)
   *                  or nonce.
   *
   * \note            Some ciphers do not use IVs nor nonce. For these
   *                  ciphers, this function has no effect.
   *
   * \param ctx       The generic cipher context. This must be initialized and
   *                  bound to a cipher information structure.
   * \param iv        The IV to use, or NONCE_COUNTER for CTR-mode ciphers. This
   *                  must be a readable buffer of at least \p iv_len Bytes.
   * \param iv_len    The IV length for ciphers with variable-size IV.
   *                  This parameter is discarded by ciphers with fixed-size IV.
   *
   * \return          \c 0 on success.
   * \return          #MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA on
   *                  parameter-verification failure.
   */
  int mbedtls_cipher_set_iv( mbedtls_cipher_context_t *ctx,
                             const unsigned char *iv,
                             size_t iv_len );
  
  /**
   * \brief         This function resets the cipher state.
   *
   * \note          With non-AEAD ciphers, the order of calls for each message
   *                is as follows:
   *                1. mbedtls_cipher_set_iv() if the mode uses an IV/nonce.
   *                2. mbedtls_cipher_reset()
   *                3. mbedtls_cipher_update() one or more times
   *                4. mbedtls_cipher_finish()
   *                .
   *                This sequence can be repeated to encrypt or decrypt multiple
   *                messages with the same key.
   *
   * \note          With AEAD ciphers, the order of calls for each message
   *                is as follows:
   *                1. mbedtls_cipher_set_iv() if the mode uses an IV/nonce.
   *                2. mbedtls_cipher_reset()
   *                3. mbedtls_cipher_update_ad()
   *                4. mbedtls_cipher_update() one or more times
   *                5. mbedtls_cipher_finish()
   *                6. mbedtls_cipher_check_tag() (for decryption) or
   *                mbedtls_cipher_write_tag() (for encryption).
   *                .
   *                This sequence can be repeated to encrypt or decrypt multiple
   *                messages with the same key.
   *
   * \param ctx     The generic cipher context. This must be bound to a key.
   *
   * \return        \c 0 on success.
   * \return        #MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA on
   *                parameter-verification failure.
   */
  int mbedtls_cipher_reset( mbedtls_cipher_context_t *ctx );
  
  #if defined(MBEDTLS_GCM_C) || defined(MBEDTLS_CHACHAPOLY_C)
  /**
   * \brief               This function adds additional data for AEAD ciphers.
   *                      Currently supported with GCM and ChaCha20+Poly1305.
   *                      This must be called exactly once, after
   *                      mbedtls_cipher_reset().
   *
   * \param ctx           The generic cipher context. This must be initialized.
   * \param ad            The additional data to use. This must be a readable
   *                      buffer of at least \p ad_len Bytes.
   * \param ad_len        The length of \p ad in Bytes.
   *
   * \return              \c 0 on success.
   * \return              A specific error code on failure.
   */
  int mbedtls_cipher_update_ad( mbedtls_cipher_context_t *ctx,
                        const unsigned char *ad, size_t ad_len );
  #endif /* MBEDTLS_GCM_C || MBEDTLS_CHACHAPOLY_C */
  
  /**
   * \brief               The generic cipher update function. It encrypts or
   *                      decrypts using the given cipher context. Writes as
   *                      many block-sized blocks of data as possible to output.
   *                      Any data that cannot be written immediately is either
   *                      added to the next block, or flushed when
   *                      mbedtls_cipher_finish() is called.
   *                      Exception: For MBEDTLS_MODE_ECB, expects a single block
   *                      in size. For example, 16 Bytes for AES.
   *
   * \param ctx           The generic cipher context. This must be initialized and
   *                      bound to a key.
   * \param input         The buffer holding the input data. This must be a
   *                      readable buffer of at least \p ilen Bytes.
   * \param ilen          The length of the input data.
   * \param output        The buffer for the output data. This must be able to
   *                      hold at least `ilen + block_size`. This must not be the
   *                      same buffer as \p input.
   * \param olen          The length of the output data, to be updated with the
   *                      actual number of Bytes written. This must not be
   *                      \c NULL.
   *
   * \return              \c 0 on success.
   * \return              #MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA on
   *                      parameter-verification failure.
   * \return              #MBEDTLS_ERR_CIPHER_FEATURE_UNAVAILABLE on an
   *                      unsupported mode for a cipher.
   * \return              A cipher-specific error code on failure.
   */
  int mbedtls_cipher_update( mbedtls_cipher_context_t *ctx,
                             const unsigned char *input,
                             size_t ilen, unsigned char *output,
                             size_t *olen );
  
  /**
   * \brief               The generic cipher finalization function. If data still
   *                      needs to be flushed from an incomplete block, the data
   *                      contained in it is padded to the size of
   *                      the last block, and written to the \p output buffer.
   *
   * \param ctx           The generic cipher context. This must be initialized and
   *                      bound to a key.
   * \param output        The buffer to write data to. This needs to be a writable
   *                      buffer of at least \p block_size Bytes.
   * \param olen          The length of the data written to the \p output buffer.
   *                      This may not be \c NULL.
   *
   * \return              \c 0 on success.
   * \return              #MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA on
   *                      parameter-verification failure.
   * \return              #MBEDTLS_ERR_CIPHER_FULL_BLOCK_EXPECTED on decryption
   *                      expecting a full block but not receiving one.
   * \return              #MBEDTLS_ERR_CIPHER_INVALID_PADDING on invalid padding
   *                      while decrypting.
   * \return              A cipher-specific error code on failure.
   */
  int mbedtls_cipher_finish( mbedtls_cipher_context_t *ctx,
                     unsigned char *output, size_t *olen );
  
  #if defined(MBEDTLS_GCM_C) || defined(MBEDTLS_CHACHAPOLY_C)
  /**
   * \brief               This function writes a tag for AEAD ciphers.
   *                      Currently supported with GCM and ChaCha20+Poly1305.
   *                      This must be called after mbedtls_cipher_finish().
   *
   * \param ctx           The generic cipher context. This must be initialized,
   *                      bound to a key, and have just completed a cipher
   *                      operation through mbedtls_cipher_finish() the tag for
   *                      which should be written.
   * \param tag           The buffer to write the tag to. This must be a writable
   *                      buffer of at least \p tag_len Bytes.
   * \param tag_len       The length of the tag to write.
   *
   * \return              \c 0 on success.
   * \return              A specific error code on failure.
   */
  int mbedtls_cipher_write_tag( mbedtls_cipher_context_t *ctx,
                        unsigned char *tag, size_t tag_len );
  
  /**
   * \brief               This function checks the tag for AEAD ciphers.
   *                      Currently supported with GCM and ChaCha20+Poly1305.
   *                      This must be called after mbedtls_cipher_finish().
   *
   * \param ctx           The generic cipher context. This must be initialized.
   * \param tag           The buffer holding the tag. This must be a readable
   *                      buffer of at least \p tag_len Bytes.
   * \param tag_len       The length of the tag to check.
   *
   * \return              \c 0 on success.
   * \return              A specific error code on failure.
   */
  int mbedtls_cipher_check_tag( mbedtls_cipher_context_t *ctx,
                        const unsigned char *tag, size_t tag_len );
  #endif /* MBEDTLS_GCM_C || MBEDTLS_CHACHAPOLY_C */
  
  /**
   * \brief               The generic all-in-one encryption/decryption function,
   *                      for all ciphers except AEAD constructs.
   *
   * \param ctx           The generic cipher context. This must be initialized.
   * \param iv            The IV to use, or NONCE_COUNTER for CTR-mode ciphers.
   *                      This must be a readable buffer of at least \p iv_len
   *                      Bytes.
   * \param iv_len        The IV length for ciphers with variable-size IV.
   *                      This parameter is discarded by ciphers with fixed-size
   *                      IV.
   * \param input         The buffer holding the input data. This must be a
   *                      readable buffer of at least \p ilen Bytes.
   * \param ilen          The length of the input data in Bytes.
   * \param output        The buffer for the output data. This must be able to
   *                      hold at least `ilen + block_size`. This must not be the
   *                      same buffer as \p input.
   * \param olen          The length of the output data, to be updated with the
   *                      actual number of Bytes written. This must not be
   *                      \c NULL.
   *
   * \note                Some ciphers do not use IVs nor nonce. For these
   *                      ciphers, use \p iv = NULL and \p iv_len = 0.
   *
   * \return              \c 0 on success.
   * \return              #MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA on
   *                      parameter-verification failure.
   * \return              #MBEDTLS_ERR_CIPHER_FULL_BLOCK_EXPECTED on decryption
   *                      expecting a full block but not receiving one.
   * \return              #MBEDTLS_ERR_CIPHER_INVALID_PADDING on invalid padding
   *                      while decrypting.
   * \return              A cipher-specific error code on failure.
   */
  int mbedtls_cipher_crypt( mbedtls_cipher_context_t *ctx,
                    const unsigned char *iv, size_t iv_len,
                    const unsigned char *input, size_t ilen,
                    unsigned char *output, size_t *olen );
  
  #if defined(MBEDTLS_CIPHER_MODE_AEAD) || defined(MBEDTLS_NIST_KW_C)
  /**
   * \brief               The authenticated encryption (AEAD/NIST_KW) function.
   *
   * \note                For AEAD modes, the tag will be appended to the
   *                      ciphertext, as recommended by RFC 5116.
   *                      (NIST_KW doesn't have a separate tag.)
   *
   * \param ctx           The generic cipher context. This must be initialized and
   *                      bound to a key, with an AEAD algorithm or NIST_KW.
   * \param iv            The nonce to use. This must be a readable buffer of
   *                      at least \p iv_len Bytes and may be \c NULL if \p
   *                      iv_len is \c 0.
   * \param iv_len        The length of the nonce. For AEAD ciphers, this must
   *                      satisfy the constraints imposed by the cipher used.
   *                      For NIST_KW, this must be \c 0.
   * \param ad            The additional data to authenticate. This must be a
   *                      readable buffer of at least \p ad_len Bytes, and may
   *                      be \c NULL is \p ad_len is \c 0.
   * \param ad_len        The length of \p ad. For NIST_KW, this must be \c 0.
   * \param input         The buffer holding the input data. This must be a
   *                      readable buffer of at least \p ilen Bytes, and may be
   *                      \c NULL if \p ilen is \c 0.
   * \param ilen          The length of the input data.
   * \param output        The buffer for the output data. This must be a
   *                      writable buffer of at least \p output_len Bytes, and
   *                      must not be \c NULL.
   * \param output_len    The length of the \p output buffer in Bytes. For AEAD
   *                      ciphers, this must be at least \p ilen + \p tag_len.
   *                      For NIST_KW, this must be at least \p ilen + 8
   *                      (rounded up to a multiple of 8 if KWP is used);
   *                      \p ilen + 15 is always a safe value.
   * \param olen          This will be filled with the actual number of Bytes
   *                      written to the \p output buffer. This must point to a
   *                      writable object of type \c size_t.
   * \param tag_len       The desired length of the authentication tag. For AEAD
   *                      ciphers, this must match the constraints imposed by
   *                      the cipher used, and in particular must not be \c 0.
   *                      For NIST_KW, this must be \c 0.
   *
   * \return              \c 0 on success.
   * \return              #MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA on
   *                      parameter-verification failure.
   * \return              A cipher-specific error code on failure.
   */
  int mbedtls_cipher_auth_encrypt_ext( mbedtls_cipher_context_t *ctx,
                           const unsigned char *iv, size_t iv_len,
                           const unsigned char *ad, size_t ad_len,
                           const unsigned char *input, size_t ilen,
                           unsigned char *output, size_t output_len,
                           size_t *olen, size_t tag_len );
  
  /**
   * \brief               The authenticated encryption (AEAD/NIST_KW) function.
   *
   * \note                If the data is not authentic, then the output buffer
   *                      is zeroed out to prevent the unauthentic plaintext being
   *                      used, making this interface safer.
   *
   * \note                For AEAD modes, the tag must be appended to the
   *                      ciphertext, as recommended by RFC 5116.
   *                      (NIST_KW doesn't have a separate tag.)
   *
   * \param ctx           The generic cipher context. This must be initialized and
   *                      bound to a key, with an AEAD algorithm or NIST_KW.
   * \param iv            The nonce to use. This must be a readable buffer of
   *                      at least \p iv_len Bytes and may be \c NULL if \p
   *                      iv_len is \c 0.
   * \param iv_len        The length of the nonce. For AEAD ciphers, this must
   *                      satisfy the constraints imposed by the cipher used.
   *                      For NIST_KW, this must be \c 0.
   * \param ad            The additional data to authenticate. This must be a
   *                      readable buffer of at least \p ad_len Bytes, and may
   *                      be \c NULL is \p ad_len is \c 0.
   * \param ad_len        The length of \p ad. For NIST_KW, this must be \c 0.
   * \param input         The buffer holding the input data. This must be a
   *                      readable buffer of at least \p ilen Bytes, and may be
   *                      \c NULL if \p ilen is \c 0.
   * \param ilen          The length of the input data. For AEAD ciphers this
   *                      must be at least \p tag_len. For NIST_KW this must be
   *                      at least \c 8.
   * \param output        The buffer for the output data. This must be a
   *                      writable buffer of at least \p output_len Bytes, and
   *                      may be \c NULL if \p output_len is \c 0.
   * \param output_len    The length of the \p output buffer in Bytes. For AEAD
   *                      ciphers, this must be at least \p ilen - \p tag_len.
   *                      For NIST_KW, this must be at least \p ilen - 8.
   * \param olen          This will be filled with the actual number of Bytes
   *                      written to the \p output buffer. This must point to a
   *                      writable object of type \c size_t.
   * \param tag_len       The actual length of the authentication tag. For AEAD
   *                      ciphers, this must match the constraints imposed by
   *                      the cipher used, and in particular must not be \c 0.
   *                      For NIST_KW, this must be \c 0.
   *
   * \return              \c 0 on success.
   * \return              #MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA on
   *                      parameter-verification failure.
   * \return              #MBEDTLS_ERR_CIPHER_AUTH_FAILED if data is not authentic.
   * \return              A cipher-specific error code on failure.
   */
  int mbedtls_cipher_auth_decrypt_ext( mbedtls_cipher_context_t *ctx,
                           const unsigned char *iv, size_t iv_len,
                           const unsigned char *ad, size_t ad_len,
                           const unsigned char *input, size_t ilen,
                           unsigned char *output, size_t output_len,
                           size_t *olen, size_t tag_len );
  #endif /* MBEDTLS_CIPHER_MODE_AEAD || MBEDTLS_NIST_KW_C */
  #ifdef __cplusplus
  }
  #endif
  
  #endif /* MBEDTLS_CIPHER_H */
  