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// Copyright 2019 Google LLC
// 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 <memory>
#include <vector>
#include "absl/synchronization/mutex.h"
#include "tink/random_access_stream.h"
#include "tink/subtle/stream_segment_decrypter.h"
#include "tink/util/statusor.h"
namespace crypto {
namespace tink {
namespace subtle {
// A RandomAccessStream that wraps another RandomAccessStream
// as a ciphertext source, and provides a "plaintext access" to
// the plaintext data contained in the ciphertext:
// - PRead()-calls to this class read appropriate segments
// of the ciphertext, decrypt them, and return the resulting
// plaintext, where the 'position' and 'count' arguments
// refer to the plaintext bytes.
// - size()-call returns the size of the entire plaintext
// if it were to be decrypted.
// Instances of this class are thread safe.
class DecryptingRandomAccessStream : public crypto::tink::RandomAccessStream {
// A factory that produces decrypting random access streams.
// The returned stream is a wrapper around 'ciphertext_source',
// such that any bytes written via the wrapper are AEAD-decrypted
// by 'segment_decrypter' using 'associated_data' as associated
// authenticated data.
static crypto::tink::util::StatusOr<
New(std::unique_ptr<StreamSegmentDecrypter> segment_decrypter,
std::unique_ptr<crypto::tink::RandomAccessStream> ciphertext_source);
// -----------------------
// Methods of RandomAccessStream-interface implemented by this class.
crypto::tink::util::Status PRead(
int64_t position, int count,
crypto::tink::util::Buffer* dest_buffer) override;
crypto::tink::util::StatusOr<int64_t> size() override;
DecryptingRandomAccessStream() {}
crypto::tink::util::Status PReadAndDecrypt(
int64_t position, int count, crypto::tink::util::Buffer* dest_buffer);
// Reads the specified ciphertext segment from ct_source_, decrypts it,
// and writes the resulting plaintext bytes to pt_segment.
// Uses the provided ct_buffer as a buffer for the ciphertext segment.
crypto::tink::util::Status ReadAndDecryptSegment(
int64_t segment_nr, crypto::tink::util::Buffer* ct_buffer,
std::vector<uint8_t>* pt_segment);
// Returns the segment number that contains the specified 'pt_position'.
int64_t GetSegmentNr(int64_t pt_position);
// Returns the offset within a segment for the specified 'pt_position'.
int GetPlaintextOffset(int64_t pt_position);
// Initializes this stream (if not initialized yet or in a permantent error)
// by reading the stream header from ct_source_ and using it initialize
// segment_decrypter_.
void InitializeIfNeeded();
std::unique_ptr<StreamSegmentDecrypter> segment_decrypter_;
std::unique_ptr<crypto::tink::RandomAccessStream> ct_source_;
mutable absl::Mutex status_mutex_;
crypto::tink::util::Status status_ ABSL_GUARDED_BY(status_mutex_);
int header_size_;
int ct_offset_;
int ct_segment_size_;
int pt_segment_size_;
int ct_segment_overhead_;
int64_t segment_count_;
int64_t pt_size_;
} // namespace subtle
} // namespace tink
} // namespace crypto