media/base/decrypt_config.h

   1 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #ifndef MEDIA_BASE_DECRYPT_CONFIG_H_
   6 #define MEDIA_BASE_DECRYPT_CONFIG_H_
   7
   8 #include <string>
   9 #include <vector>
  10
  11 #include "base/basictypes.h"
  12 #include "base/memory/scoped_ptr.h"
  13 #include "media/base/media_export.h"
  14
  15 namespace media {
  16
  17 // The Common Encryption spec provides for subsample encryption, where portions
  18 // of a sample are set in cleartext. A SubsampleEntry specifies the number of
  19 // clear and encrypted bytes in each subsample. For decryption, all of the
  20 // encrypted bytes in a sample should be considered a single logical stream,
  21 // regardless of how they are divided into subsamples, and the clear bytes
  22 // should not be considered as part of decryption. This is logically equivalent
  23 // to concatenating all 'cypher_bytes' portions of subsamples, decrypting that
  24 // result, and then copying each byte from the decrypted block over the
  25 // position of the corresponding encrypted byte.
  26 struct SubsampleEntry {
  27   uint32 clear_bytes;
  28   uint32 cypher_bytes;
  29 };
  30
  31 // Contains all information that a decryptor needs to decrypt a media sample.
  32 class MEDIA_EXPORT DecryptConfig {
  33  public:
  34   // Keys are always 128 bits.
  35   static const int kDecryptionKeySize = 16;
  36
  37   // |key_id| is the ID that references the decryption key for this sample.
  38   // |iv| is the initialization vector defined by the encrypted format.
  39   //   Currently |iv| must be 16 bytes as defined by WebM and ISO. Or must be
  40   //   empty which signals an unencrypted frame.
  41   // |data_offset| is the amount of data that should be discarded from the
  42   //   head of the sample buffer before applying subsample information. A
  43   //   decrypted buffer will be shorter than an encrypted buffer by this amount.
  44   // |subsamples| defines the clear and encrypted portions of the sample as
  45   //   described above. A decrypted buffer will be equal in size to the sum
  46   //   of the subsample sizes.
  47   //
  48   // |data_offset| is applied before |subsamples|.
  49   DecryptConfig(const std::string& key_id,
  50                 const std::string& iv,
  51                 const int data_offset,
  52                 const std::vector<SubsampleEntry>& subsamples);
  53   ~DecryptConfig();
  54
  55   const std::string& key_id() const { return key_id_; }
  56   const std::string& iv() const { return iv_; }
  57   int data_offset() const { return data_offset_; }
  58   const std::vector<SubsampleEntry>& subsamples() const { return subsamples_; }
  59
  60  private:
  61   const std::string key_id_;
  62
  63   // Initialization vector.
  64   const std::string iv_;
  65
  66   // TODO(fgalligan): Remove |data_offset_| if there is no plan to use it in
  67   // the future.
  68   // Amount of data to be discarded before applying subsample information.
  69   const int data_offset_;
  70
  71   // Subsample information. May be empty for some formats, meaning entire frame
  72   // (less data ignored by data_offset_) is encrypted.
  73   const std::vector<SubsampleEntry> subsamples_;
  74
  75   DISALLOW_COPY_AND_ASSIGN(DecryptConfig);
  76 };
  77
  78 }  // namespace media
  79
  80 #endif  // MEDIA_BASE_DECRYPT_CONFIG_H_