text: /**
   * Copyright (c) 2019, Nordic Semiconductor ASA
   *
   * All rights reserved.
   *
   * Redistribution and use in source and binary forms, with or without modification,
   * are permitted provided that the following conditions are met:
   *
   * 1. Redistributions of source code must retain the above copyright notice, this
   *    list of conditions and the following disclaimer.
   *
   * 2. Redistributions in binary form, except as embedded into a Nordic
   *    Semiconductor ASA integrated circuit in a product or a software update for
   *    such product, must reproduce the above copyright notice, this list of
   *    conditions and the following disclaimer in the documentation and/or other
   *    materials provided with the distribution.
   *
   * 3. Neither the name of Nordic Semiconductor ASA nor the names of its
   *    contributors may be used to endorse or promote products derived from this
   *    software without specific prior written permission.
   *
   * 4. This software, with or without modification, must only be used with a
   *    Nordic Semiconductor ASA integrated circuit.
   *
   * 5. Any software provided in binary form under this license must not be reverse
   *    engineered, decompiled, modified and/or disassembled.
   *
   * THIS SOFTWARE IS PROVIDED BY NORDIC SEMICONDUCTOR ASA "AS IS" AND ANY EXPRESS
   * OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
   * OF MERCHANTABILITY, NONINFRINGEMENT, AND FITNESS FOR A PARTICULAR PURPOSE ARE
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   *
   */
  
  /**@file
   * @defgroup nrf_oberon_srpt SRPT - Secure Real-Time Transport Protocol APIs
   * @ingroup nrf_oberon
   * @{
   * @brief Type declarations and APIs for SRTP - Secure Real-time Transport Protocol.
   */
  
  #ifndef OCRYPTO_SRTP_H
  #define OCRYPTO_SRTP_H
  
  #ifdef __cplusplus
  extern "C" {
  #endif
  
  #include <stddef.h>
  #include <stdint.h>
  
  #include "ocrypto_aes_key.h"
  
  /**
   * SRTP Authentication Key Size.
   */
  #define ocrypto_srtp_AuthKeySize  (20)
  
  /**
   * SRTP Salt Size.
   */
  #define ocrypto_srtp_SaltSize     (14)
  
  /**
   * SRTP Maximum Key Size.
   */
  #define ocrypto_srtp_MaxKeySize   (ocrypto_aes256_KEY_BYTES)
  
  /**
   * SRTP Context.
   */
  typedef struct {
      /**
       * Key size [bytes].
       */
      uint32_t keySize;
  
      /**
       * Tag size [bytes].
       */
      uint32_t tagSize;
  
      /**
       * Session encryption key (max 256 bits).
       */
      uint8_t encrKey[ocrypto_srtp_MaxKeySize];
  
      /**
       * Session authentication key
       * 160 bits.
       */
      uint8_t authKey[ocrypto_srtp_AuthKeySize];
  
      /**
       * Session salt
       * 112 bits.
       */
      uint8_t saltKey[ocrypto_srtp_SaltSize];
  } ocrypto_srtp_context;
  
  /**
   * Set up SRTP contexts.
   *
   * @param[out] srtpContext          SRTP context to be set up.
   * @param[out] srtcpContext         SRTCP context to be set up.
   * @param      key                  Master key.
   * @param      keySize              Size of the master key (16, 24, or 32 bytes)
   * @param      salt                 Master salt.
   * @param      tagSize              Size of the authentication tag.
   * @param      ssrc                 Synchronization source.
   */
  void ocrypto_srtp_setupContext(
      ocrypto_srtp_context *srtpContext,
      ocrypto_srtp_context *srtcpContext,
      const uint8_t *key,
      uint32_t keySize,
      const uint8_t *salt,
      uint32_t tagSize,
      uint32_t ssrc);
  
  /**
   * Encrypt SRTP packet.
   *
   * The final packet consists of @p numHeaderBytes encrytped in place, followed
   * by @p numDataBytes copied from @p dataBytes during encryption.
   *
   * @param         srtpContext          SRTP context.
   * @param[in,out] packet               Encrypted packet.
   * @param         dataBytes            Data bytes to be encrypted.
   * @param         numHeaderBytes       Number of header bytes.
   * @param         numDataBytes         Number of data bytes.
   * @param         index                Packet index.
   */
  void ocrypto_srtp_encrypt(
      const ocrypto_srtp_context *srtpContext,
      uint8_t *packet,
      const uint8_t *dataBytes,
      size_t numHeaderBytes,
      size_t numDataBytes,
      uint32_t index);
  
  /**
   * Decrypt SRTP packet.
   *
   * @param      srtpContext          SRTP context.
   * @param[out] data                 Decrypted data.
   * @param      packetBytes          Packet bytes.
   * @param      numPacketBytes       Number of packet bytes.
   * @param      index                Packet index.
   */
  void ocrypto_srtp_decrypt(
      const ocrypto_srtp_context *srtpContext,
      uint8_t *data,
      const uint8_t *packetBytes,
      size_t numPacketBytes,
      uint32_t index);
  
  /**
   * Generate SRTP authentication tag from bytes and index.
   *
   * @param      context              SRTP context.
   * @param[out] tag                  Authentication tag generated.
   * @param      bytes                Byte buffer.
   * @param      numBytes             Number of bytes in buffer.
   * @param      index                Index.
   */
  void ocrypto_srtp_authenticate(
      const ocrypto_srtp_context *context,
      uint8_t *tag,
      const uint8_t *bytes,
      size_t numBytes,
      uint32_t index);
  
  /**
   * Check SRTP authentication tag against bytes and index.
   *
   * @param      context              SRTP context.
   * @param      tag                  Tag.
   * @param      bytes                Byte buffer.
   * @param      numBytes             Number of bytes in buffer.
   * @param      index                Index.
   *
   * @retval 1 If the tag is valid.
   * @retval 0 Otherwise. 
   */
  int ocrypto_srtp_verifyAuthentication(
      ocrypto_srtp_context *context,
      const uint8_t *tag,
      const uint8_t *bytes,
      size_t numBytes,
      uint32_t index);
  
  #ifdef __cplusplus
  }
  #endif
  
  #endif
  
  /** @} */
  