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// Copyright 2019 Google Inc.
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// See the License for the specific language governing permissions and
// limitations under the License.
#include <cstdint>
#include <vector>
#include "tink/util/status.h"
namespace crypto {
namespace tink {
namespace subtle {
// StreamSegmentDecrypter is a helper class that decrypts individual
// segments of a stream.
// Instances of this are passed to an ...DecryptingStream. Each instance
// of a segment decrypter must be initialized with a header of a ciphertext
// stream and is used to decrypt that stream.
// See stream_segment_encrypter.h for more info on the structure of
// a ciphertext stream.
class StreamSegmentDecrypter {
// Decrypts 'ciphertext' as a segment, and writes the resulting plaintext
// to 'plaintext_buffer', adjusting its size as needed.
// 'ciphertext' and 'plaintext_buffer' must refer to distinct and
// non-overlapping space.
// Decryption uses the current value returned by get_segment_number()
// as the segment number, and subsequently increments the current
// segment number.
virtual util::Status DecryptSegment(
const std::vector<uint8_t>& ciphertext,
int64_t segment_number,
bool is_last_segment,
std::vector<uint8_t>* plaintext_buffer) = 0;
// Initializes this decrypter, using the information from 'header',
// which must be of size exactly get_header_size().
virtual util::Status Init(const std::vector<uint8_t>& header) = 0;
// Returns the size (in bytes) of the header of a ciphertext stream.
virtual int get_header_size() const = 0;
// Returns the size (in bytes) of a plaintext segment.
virtual int get_plaintext_segment_size() const = 0;
// Returns the size (in bytes) of a ciphertext segment.
virtual int get_ciphertext_segment_size() const = 0;
// Returns the offset (in bytes) of the ciphertext within an decrypted stream.
// The offset is non-negative, and not larger than
// ciphertext_segment_size - (header_size + segment_overhead)
// where
// ciphertext_segment_size = get_ciphertext_segment_size()
// header_size = get_header_size()
// segment_overhead = ciphertext_segment_size - get_plaintext_segment_size()
virtual int get_ciphertext_offset() const = 0;
virtual ~StreamSegmentDecrypter() {}
} // namespace subtle
} // namespace tink
} // namespace crypto