arc4.cpp

// arc4.cpp - originally written and placed in the public domain by Wei Dai
 
// The ARC4 algorithm was first revealed in an anonymous email to the
// cypherpunks mailing list. This file originally contained some
// code copied from this email. The code has since been rewritten in order
// to clarify the copyright status of this file. It should now be
// completely in the public domain.
 
#include "pch.h"
#define CRYPTOPP_ENABLE_NAMESPACE_WEAK 1
#include "arc4.h"
 
NAMESPACE_BEGIN(CryptoPP)
namespace Weak1 {
 
#if defined(CRYPTOPP_DEBUG) && !defined(CRYPTOPP_DOXYGEN_PROCESSING)
void ARC4_TestInstantiations()
{
    ARC4 x;
}
#endif
 
ARC4_Base::~ARC4_Base()
{
    m_x = m_y = 0;
}
 
void ARC4_Base::UncheckedSetKey(const byte *key, unsigned int length, const NameValuePairs &params)
{
    AssertValidKeyLength(length);
 
    m_x = 1;
    m_y = 0;
 
    unsigned int i;
    for (i=0; i<256; i++)
        m_state[i] = byte(i);
 
    unsigned int keyIndex = 0, stateIndex = 0;
    for (i=0; i<256; i++)
    {
        unsigned int a = m_state[i];
        stateIndex += key[keyIndex] + a;
        stateIndex &= 0xff;
        m_state[i] = m_state[stateIndex];
        m_state[stateIndex] = byte(a);
        if (++keyIndex >= length)
            keyIndex = 0;
    }
 
    int discardBytes = params.GetIntValueWithDefault("DiscardBytes", GetDefaultDiscardBytes());
    DiscardBytes(discardBytes);
}
 
template <class T>
static inline unsigned int MakeByte(T &x, T &y, byte *s)
{
    unsigned int a = s[x];
    y = byte((y+a) & 0xff);
    unsigned int b = s[y];
    s[x] = byte(b);
    s[y] = byte(a);
    x = byte((x+1) & 0xff);
    return s[(a+b) & 0xff];
}
 
void ARC4_Base::GenerateBlock(byte *output, size_t size)
{
    while (size--)
        *output++ = static_cast<byte>(MakeByte(m_x, m_y, m_state));
}
 
void ARC4_Base::ProcessData(byte *outString, const byte *inString, size_t length)
{
    if (length == 0)
        return;
 
    byte *const s = m_state;
    unsigned int x = m_x;
    unsigned int y = m_y;
 
    if (inString == outString)
    {
        do
        {
            *outString++ ^= MakeByte(x, y, s);
        } while (--length);
    }
    else
    {
        do
        {
            *outString++ = *inString++ ^ byte(MakeByte(x, y, s));
        }
        while(--length);
    }
 
    m_x = byte(x);
    m_y = byte(y);
}
 
void ARC4_Base::DiscardBytes(size_t n)
{
    if (n == 0)
        return;
 
    byte *const s = m_state;
    unsigned int x = m_x;
    unsigned int y = m_y;
 
    do
    {
        MakeByte(x, y, s);
    }
    while(--n);
 
    m_x = byte(x);
    m_y = byte(y);
}
 
}
NAMESPACE_END