ARCFOUR implemenation

ARCFOUR.h

/*
ARCFOUR.h -- ARCFOUR implemenation

Copyright 2018 yni3
License : Public Domain (useful for copy and paste for your project)
*/

#pragma once

#ifndef __ARCFOUR
#define __ARCFOUR

class ARCFOUR
{
	static constexpr unsigned int N = 255;

	//Conversion table
	unsigned char m_S[N];
	int i = 0, j = 0;

	inline  void swap(unsigned char *a, unsigned char *b) const {
		int tmp = *a;
		*a = *b;
		*b = tmp;
	}

	void KSA(const unsigned char *key, int key_len, unsigned char *S) const {
		int j = 0;
		for (int i = 0; i < N; i++)
			S[i] = i;
		for (int i = 0; i < N; i++) {
			j = (j + S[i] + key[i % key_len]) % N;

			swap(&S[i], &S[j]);
		}
	}

	void PRGA(unsigned char *S, unsigned char *dst, const unsigned char *src, int srclen) {
		for (size_t n = 0, len = srclen; n < len; n++) {
			i = (i + 1) % N;
			j = (j + S[i]) % N;
			swap(&S[i], &S[j]);
			int rnd = S[(S[i] + S[j]) % N];
			dst[n] = rnd ^ src[n];
		}
	}

public:
	ARCFOUR()
		: m_S(), i(0), j(0)
	{
	}
	ARCFOUR(const unsigned char *key, int key_len)
	{
		KSA(key, key_len, m_S);
	}
	virtual ~ARCFOUR() {};

	//call straightforward encrypt
	//call reverse decrypt
	void RC4(unsigned char *dst, const unsigned char *src, int srclen) {
		PRGA(m_S, dst, src, srclen);
	}

};

#endif