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// SPDX-FileCopyrightText: Copyright 2025 Eden Emulator Project
// SPDX-License-Identifier: GPL-3.0-or-later
// SPDX-FileCopyrightText: Copyright 2018 yuzu Emulator Project
// SPDX-License-Identifier: GPL-2.0-or-later
#include <algorithm>
#include <array>
#include <cstring>
#include "core/crypto/xts_encryption_layer.h"
namespace Core::Crypto {
constexpr std::size_t XTS_SECTOR_SIZE = 0x4000;
XTSEncryptionLayer::XTSEncryptionLayer(FileSys::VirtualFile base_, Key256 key_)
: EncryptionLayer(std::move(base_)), cipher(key_, Mode::XTS) {}
std::size_t XTSEncryptionLayer::Read(u8* data, std::size_t length, std::size_t offset) const {
if (length == 0)
return 0;
constexpr std::size_t PrefetchSectors = 4;
auto* out = data;
std::size_t remaining = length;
std::size_t current_offset = offset;
std::size_t total_read = 0;
std::array<u8, XTS_SECTOR_SIZE> sector{};
while (remaining > 0) {
const std::size_t sector_index = current_offset / XTS_SECTOR_SIZE;
const std::size_t sector_offset = current_offset % XTS_SECTOR_SIZE;
const std::size_t sectors_to_read = std::min<std::size_t>(PrefetchSectors,
(remaining + sector_offset +
XTS_SECTOR_SIZE - 1) /
XTS_SECTOR_SIZE);
for (std::size_t s = 0; s < sectors_to_read && remaining > 0; ++s) {
const std::size_t index = sector_index + s;
const std::size_t read_offset = index * XTS_SECTOR_SIZE;
const std::size_t got = base->Read(sector.data(), XTS_SECTOR_SIZE, read_offset);
if (got == 0)
return total_read;
if (got < XTS_SECTOR_SIZE)
std::memset(sector.data() + got, 0, XTS_SECTOR_SIZE - got);
cipher.XTSTranscode(sector.data(), XTS_SECTOR_SIZE, sector.data(), index, XTS_SECTOR_SIZE,
Op::Decrypt);
const std::size_t local_offset = (s == 0) ? sector_offset : 0;
const std::size_t available = XTS_SECTOR_SIZE - local_offset;
const std::size_t to_copy = std::min<std::size_t>(available, remaining);
std::memcpy(out, sector.data() + local_offset, to_copy);
out += to_copy;
current_offset += to_copy;
remaining -= to_copy;
total_read += to_copy;
}
}
return total_read;
}
} // namespace Core::Crypto
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