| // Copyright 2015 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 CHROMECAST_PUBLIC_MEDIA_CAST_DECRYPT_CONFIG_H_ |
| #define CHROMECAST_PUBLIC_MEDIA_CAST_DECRYPT_CONFIG_H_ |
| |
| #include <stdint.h> |
| #include <string> |
| #include <vector> |
| |
| namespace chromecast { |
| namespace media { |
| |
| // Specification of whether and how the stream is encrypted (in whole or part). |
| // |
| // Algorithm and mode that was used to encrypt the stream. |
| enum class EncryptionScheme { kUnencrypted, kAesCtr, kAesCbc }; |
| |
| // CENC 3rd Edition adds pattern encryption, through two new protection |
| // schemes: 'cens' (with AES-CTR) and 'cbcs' (with AES-CBC). |
| // The pattern applies independently to each 'encrypted' part of the frame (as |
| // defined by the relevant subsample entries), and reduces further the |
| // actual encryption applied through a repeating pattern of (encrypt:skip) |
| // 16 byte blocks. For example, in a (1:9) pattern, the first block is |
| // encrypted, and the next nine are skipped. This pattern is applied |
| // repeatedly until the end of the last 16-byte block in the subsample. |
| // Any remaining bytes are left clear. |
| // If either of encrypt_blocks or skip_blocks is 0, pattern encryption is |
| // disabled. |
| struct EncryptionPattern { |
| EncryptionPattern() = default; |
| EncryptionPattern(uint32_t encrypt_blocks, uint32_t skip_blocks); |
| bool IsInEffect() const; |
| |
| uint32_t encrypt_blocks = 0; |
| uint32_t skip_blocks = 0; |
| }; |
| |
| inline EncryptionPattern::EncryptionPattern(uint32_t encrypt_blocks, |
| uint32_t skip_blocks) |
| : encrypt_blocks(encrypt_blocks), skip_blocks(skip_blocks) {} |
| |
| inline bool EncryptionPattern::IsInEffect() const { |
| return encrypt_blocks != 0 && skip_blocks != 0; |
| } |
| |
| // 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 { |
| SubsampleEntry() : clear_bytes(0), cypher_bytes(0) {} |
| SubsampleEntry(uint32_t clear_bytes, uint32_t cypher_bytes) |
| : clear_bytes(clear_bytes), cypher_bytes(cypher_bytes) {} |
| uint32_t clear_bytes; |
| uint32_t cypher_bytes; |
| }; |
| |
| // Contains all metadata needed to decrypt a media sample. |
| class CastDecryptConfig { |
| public: |
| virtual ~CastDecryptConfig() = default; |
| |
| // Returns the ID for this sample's decryption key. |
| virtual const std::string& key_id() const = 0; |
| |
| // Returns the initialization vector as defined by the encryption format. |
| virtual const std::string& iv() const = 0; |
| |
| // Returns the encryption pattern for current sample. |
| virtual const EncryptionPattern& pattern() const = 0; |
| |
| // Returns the clear and encrypted portions of the sample as described above. |
| virtual const std::vector<SubsampleEntry>& subsamples() const = 0; |
| }; |
| |
| } // namespace media |
| } // namespace chromecast |
| |
| #endif // CHROMECAST_PUBLIC_MEDIA_CAST_DECRYPT_CONFIG_H_ |