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