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