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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this file,
* You can obtain one at http://mozilla.org/MPL/2.0/. */
#ifndef mozilla_dom_quota_EncryptedBlock_h
#define mozilla_dom_quota_EncryptedBlock_h
#include <cstdint>
#include <cstring>
#include <limits>
#include "mozilla/Assertions.h"
#include "mozilla/Span.h"
#include "nsTArray.h"
namespace mozilla::dom::quota {
// An encrypted block has the following format:
// - one basic block containing a uint16_t stating the actual payload length
// - one basic block containing the cipher prefix (tyipically a nonce)
// - encrypted payload up to the remainder of the specified overall size
// We currently assume the basic block size is the same as the cipher prefix
// length.
//
// XXX Actually, we don't need the actual payload length in every block. Only
// the last block may be incomplete. The tricky thing is just that it might be
// incomplete by just one or two bytes.
template <size_t CipherPrefixLength, size_t BasicBlockSize>
class EncryptedBlock {
public:
explicit EncryptedBlock(const size_t aOverallSize) {
MOZ_RELEASE_ASSERT(aOverallSize >
CipherPrefixOffset() + CipherPrefixLength);
MOZ_RELEASE_ASSERT(aOverallSize <= std::numeric_limits<uint16_t>::max());
// XXX Do we need this to be fallible? Then we need a factory/init function.
// But maybe that's not necessary as the block size is not user-provided and
// small.
mData.SetLength(aOverallSize);
// Bug 1867394: Making sure to zero-initialize first block as there might
// be some unused bytes in it which could expose sensitive data.
// Currently, only sizeof(uint16_t) bytes gets used in the first block.
std::fill(mData.begin(), mData.begin() + CipherPrefixOffset(), 0);
SetActualPayloadLength(MaxPayloadLength());
}
size_t MaxPayloadLength() const {
return mData.Length() - CipherPrefixLength - CipherPrefixOffset();
}
void SetActualPayloadLength(uint16_t aActualPayloadLength) {
memcpy(mData.Elements(), &aActualPayloadLength, sizeof(uint16_t));
}
size_t ActualPayloadLength() const {
return *reinterpret_cast<const uint16_t*>(mData.Elements());
}
using ConstSpan = Span<const uint8_t>;
using MutableSpan = Span<uint8_t>;
ConstSpan CipherPrefix() const {
return WholeBlock().Subspan(CipherPrefixOffset(), CipherPrefixLength);
}
MutableSpan MutableCipherPrefix() {
return MutableWholeBlock().Subspan(CipherPrefixOffset(),
CipherPrefixLength);
}
ConstSpan Payload() const {
return WholeBlock()
.SplitAt(CipherPrefixOffset() + CipherPrefixLength)
.second.First(RoundedUpToBasicBlockSize(ActualPayloadLength()));
}
MutableSpan MutablePayload() {
return MutableWholeBlock()
.SplitAt(CipherPrefixOffset() + CipherPrefixLength)
.second.First(RoundedUpToBasicBlockSize(ActualPayloadLength()));
}
ConstSpan WholeBlock() const { return mData; }
MutableSpan MutableWholeBlock() { return mData; }
private:
static constexpr size_t CipherPrefixOffset() {
return RoundedUpToBasicBlockSize(sizeof(uint16_t));
}
static constexpr size_t RoundedUpToBasicBlockSize(const size_t aValue) {
return (aValue + BasicBlockSize - 1) / BasicBlockSize * BasicBlockSize;
}
nsTArray<uint8_t> mData;
};
} // namespace mozilla::dom::quota
#endif
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