RC4.cpp

#include "RC4.h"

void RC4::exchb(BYTE *b1, BYTE *b2)
{
    BYTE tmp = *b1;
    *b1 = *b2;
    *b2 = tmp;
}

RC4::RC4(const BYTE *bpKey, DWORD dwKeyLen)
{
    this->bpKey = new BYTE[dwKeyLen];
    memcpy(this->bpKey, bpKey, dwKeyLen);
    this->dwKeyLen = dwKeyLen;
    this->SBOX = new BYTE[256];
    this->initSBOX();
}

void RC4::initSBOX()
{
    int i = 0, j = 0;

    for(i = 0; i < 256; i++)
        this->SBOX[i] = i;

    for(i = 0; i < 256; i++)
    {
        j = (j + this->SBOX[i] + this->bpKey[i % this->dwKeyLen]) % 256;
        this->exchb(&this->SBOX[i], &this->SBOX[j]);
    }
}

void RC4::encrypt(BYTE *msg, DWORD mlen)
{
    int i = 0, j = 0;

    for(DWORD itr = 0; itr < mlen; itr++)
    {
        i = (i + 1) % 256;
        j = (j + this->SBOX[i]) % 256;
        this->exchb(&this->SBOX[i], &this->SBOX[j]);
        msg[itr]  = msg[itr] ^ this->SBOX[(this->SBOX[i] + this->SBOX[j]) % 256];
    }
    this->initSBOX();
}