81 lines
2.0 KiB
C
81 lines
2.0 KiB
C
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// This file Copyright © 2021-2022 Mike Gelfand
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// It may be used under the 3-clause BSD (SPDX: BSD-3-Clause).
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// License text can be found in the licenses/ folder.
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#pragma once
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#include <array>
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#include <cstddef> // size_t
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#include <cstdint> // uint8_t
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/**
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* This is a tiny and reusable implementation of alleged RC4 cipher.
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* https://en.wikipedia.org/wiki/RC4
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*
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* The use of RC4 is declining due to security concerns.
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* Popular cryptographic libraries have deprecated or removed it:
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*
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* - OpenSSL: disabled by default in 1.1, moved to "legacy" in 3.0
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* - WolfSSL (CyaSSL): disabled by default in 3.4.6
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* - MbedTLS (PolarSSL): removed in 3.0
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*
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* Nonetheless it's still used in BitTorrent Protocol Encryption
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* https://en.wikipedia.org/wiki/BitTorrent_protocol_encryption,
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* so this header file provides an implementation.
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*/
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class tr_arc4
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{
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public:
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constexpr tr_arc4(void const* key, size_t key_length)
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{
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for (size_t i = 0; i < 256; ++i)
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{
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s_[i] = static_cast<uint8_t>(i);
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}
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for (size_t i = 0, j = 0; i < 256; ++i)
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{
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j = static_cast<uint8_t>(j + s_[i] + ((uint8_t const*)key)[i % key_length]);
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arc4_swap(i, j);
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}
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}
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constexpr void process(void const* src_data, void* dst_data, size_t data_length)
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{
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for (size_t i = 0; i < data_length; ++i)
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{
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((uint8_t*)dst_data)[i] = ((uint8_t const*)src_data)[i] ^ arc4_next();
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}
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}
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constexpr void discard(size_t length)
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{
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while (length-- > 0)
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{
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arc4_next();
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}
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}
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private:
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constexpr void arc4_swap(size_t i, size_t j)
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{
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auto const tmp = s_[i];
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s_[i] = s_[j];
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s_[j] = tmp;
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}
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constexpr uint8_t arc4_next()
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{
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i_ += 1;
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j_ += s_[i_];
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arc4_swap(i_, j_);
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return s_[static_cast<uint8_t>(s_[i_] + s_[j_])];
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}
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uint8_t i_ = 0;
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uint8_t j_ = 0;
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std::array<uint8_t, 256> s_ = {};
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};
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