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 // Copyright (c) 2012 The Chromium Authors. All rights reserved.

 // Use of this source code is governed by a BSD-style license that can be

 // found in the LICENSE file.

 #ifndef MEDIA_BASE_DECRYPT_CONFIG_H_

 #define MEDIA_BASE_DECRYPT_CONFIG_H_

 #include <string>

 #include <vector>

 #include "mp4_demuxer/basictypes.h"

 namespace mp4_demuxer {

 // The Common Encryption spec provides for subsample encryption, where portions

 // of a sample are set in cleartext. A SubsampleEntry specifies the number of

 // clear and encrypted bytes in each subsample. For decryption, all of the

 // encrypted bytes in a sample should be considered a single logical stream,

 // regardless of how they are divided into subsamples, and the clear bytes

 // should not be considered as part of decryption. This is logically equivalent

 // to concatenating all 'cypher_bytes' portions of subsamples, decrypting that

 // result, and then copying each byte from the decrypted block over the

 // position of the corresponding encrypted byte.

 struct SubsampleEntry {

   uint32_t clear_bytes;

   uint32_t cypher_bytes;

 };

 // Contains all information that a decryptor needs to decrypt a media sample.

 class DecryptConfig {

  public:

   // Keys are always 128 bits.

   static const int kDecryptionKeySize = 16;

   // |key_id| is the ID that references the decryption key for this sample.

   // |iv| is the initialization vector defined by the encrypted format.

   //   Currently |iv| must be 16 bytes as defined by WebM and ISO. Or must be

   //   empty which signals an unencrypted frame.

   // |data_offset| is the amount of data that should be discarded from the

   //   head of the sample buffer before applying subsample information. A

   //   decrypted buffer will be shorter than an encrypted buffer by this amount.

   // |subsamples| defines the clear and encrypted portions of the sample as

   //   described above. A decrypted buffer will be equal in size to the sum

   //   of the subsample sizes.

   //

   // |data_offset| is applied before |subsamples|.

   DecryptConfig(const std::string& key_id,

                 const std::string& iv,

                 const int data_offset,

                 const std::vector<SubsampleEntry>& subsamples);

   ~DecryptConfig();

   const std::string& key_id() const { return key_id_; }

   const std::string& iv() const { return iv_; }

   int data_offset() const { return data_offset_; }

   const std::vector<SubsampleEntry>& subsamples() const { return subsamples_; }

  private:

   const std::string key_id_;

   // Initialization vector.

   const std::string iv_;

   // TODO(fgalligan): Remove |data_offset_| if there is no plan to use it in

   // the future.

   // Amount of data to be discarded before applying subsample information.

   const int data_offset_;

   // Subsample information. May be empty for some formats, meaning entire frame

   // (less data ignored by data_offset_) is encrypted.

   const std::vector<SubsampleEntry> subsamples_;

   DISALLOW_COPY_AND_ASSIGN(DecryptConfig);

 };

 }  // namespace mp4_demuxer

 #endif  // MEDIA_BASE_DECRYPT_CONFIG_H_