xref: /aosp_15_r20/external/tink/cc/subtle/stream_segment_decrypter.h (revision e7b1675dde1b92d52ec075b0a92829627f2c52a5)
1 // Copyright 2019 Google Inc.
2 //
3 // Licensed under the Apache License, Version 2.0 (the "License");
4 // you may not use this file except in compliance with the License.
5 // You may obtain a copy of the License at
6 //
7 //     http://www.apache.org/licenses/LICENSE-2.0
8 //
9 // Unless required by applicable law or agreed to in writing, software
10 // distributed under the License is distributed on an "AS IS" BASIS,
11 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12 // See the License for the specific language governing permissions and
13 // limitations under the License.
14 //
15 ///////////////////////////////////////////////////////////////////////////////
16 
17 #ifndef TINK_SUBTLE_STREAM_SEGMENT_DECRYPTER_H_
18 #define TINK_SUBTLE_STREAM_SEGMENT_DECRYPTER_H_
19 
20 #include <cstdint>
21 #include <vector>
22 
23 #include "tink/util/status.h"
24 
25 namespace crypto {
26 namespace tink {
27 namespace subtle {
28 
29 // StreamSegmentDecrypter is a helper class that decrypts individual
30 // segments of a stream.
31 //
32 // Instances of this are passed to an ...DecryptingStream. Each instance
33 // of a segment decrypter must be initialized with a header of a ciphertext
34 // stream and is used to decrypt that stream.
35 //
36 // See stream_segment_encrypter.h for more info on the structure of
37 // a ciphertext stream.
38 class StreamSegmentDecrypter {
39  public:
40   // Decrypts 'ciphertext' as a segment, and writes the resulting plaintext
41   // to 'plaintext_buffer', adjusting its size as needed.
42   // 'ciphertext' and 'plaintext_buffer' must refer to distinct and
43   // non-overlapping space.
44   // Decryption uses the current value returned by get_segment_number()
45   // as the segment number, and subsequently increments the current
46   // segment number.
47   virtual util::Status DecryptSegment(
48       const std::vector<uint8_t>& ciphertext,
49       int64_t segment_number,
50       bool is_last_segment,
51       std::vector<uint8_t>* plaintext_buffer) = 0;
52 
53   // Initializes this decrypter, using the information from 'header',
54   // which must be of size exactly get_header_size().
55   virtual util::Status Init(const std::vector<uint8_t>& header) = 0;
56 
57   // Returns the size (in bytes) of the header of a ciphertext stream.
58   virtual int get_header_size() const = 0;
59 
60   // Returns the size (in bytes) of a plaintext segment.
61   virtual int get_plaintext_segment_size() const = 0;
62 
63   // Returns the size (in bytes) of a ciphertext segment.
64   virtual int get_ciphertext_segment_size() const = 0;
65 
66   // Returns the offset (in bytes) of the ciphertext within an decrypted stream.
67   // The offset is non-negative, and not larger than
68   //   ciphertext_segment_size - (header_size + segment_overhead)
69   // where
70   //   ciphertext_segment_size = get_ciphertext_segment_size()
71   //   header_size = get_header_size()
72   //   segment_overhead = ciphertext_segment_size - get_plaintext_segment_size()
73   virtual int get_ciphertext_offset() const = 0;
74 
75   virtual ~StreamSegmentDecrypter() = default;
76 };
77 
78 }  // namespace subtle
79 }  // namespace tink
80 }  // namespace crypto
81 
82 #endif  // TINK_SUBTLE_STREAM_SEGMENT_DECRYPTER_H_
83