rc5.cpp

// rc5.cpp - originally written and placed in the public domain by Wei Dai
 
#include "pch.h"
#include "rc5.h"
#include "misc.h"
#include "secblock.h"
 
NAMESPACE_BEGIN(CryptoPP)
 
void RC5::Base::UncheckedSetKey(const byte *k, unsigned int keylen, const NameValuePairs &params)
{
    AssertValidKeyLength(keylen);
 
    r = GetRoundsAndThrowIfInvalid(params, this);
    sTable.New(2*(r+1));
 
    static const RC5_WORD MAGIC_P = 0xb7e15163L;    // magic constant P for wordsize
    static const RC5_WORD MAGIC_Q = 0x9e3779b9L;    // magic constant Q for wordsize
    static const int U=sizeof(RC5_WORD);
 
    const unsigned int c = STDMAX((keylen+U-1)/U, 1U);  // RC6 paper says c=1 if keylen==0
    SecBlock<RC5_WORD> l(c);
 
    GetUserKey(LITTLE_ENDIAN_ORDER, l.begin(), c, k, keylen);
 
    sTable[0] = MAGIC_P;
    for (unsigned j=1; j<sTable.size();j++)
        sTable[j] = sTable[j-1] + MAGIC_Q;
 
    RC5_WORD a=0, b=0;
    const unsigned n = 3*STDMAX((unsigned int)sTable.size(), c);
 
    for (unsigned h=0; h < n; h++)
    {
        a = sTable[h % sTable.size()] = rotlConstant<3>((sTable[h % sTable.size()] + a + b));
        b = l[h % c] = rotlMod((l[h % c] + a + b), (a+b));
    }
}
 
typedef BlockGetAndPut<RC5::RC5_WORD, LittleEndian> Block;
 
void RC5::Enc::ProcessAndXorBlock(const byte *inBlock, const byte *xorBlock, byte *outBlock) const
{
    const RC5_WORD *sptr = sTable;
    RC5_WORD a, b;
 
    Block::Get(inBlock)(a)(b);
    a += sptr[0];
    b += sptr[1];
    sptr += 2;
 
    for(unsigned i=0; i<r; i++)
    {
        a = rotlMod(a^b,b) + sptr[2*i+0];
        b = rotlMod(a^b,a) + sptr[2*i+1];
    }
 
    Block::Put(xorBlock, outBlock)(a)(b);
}
 
void RC5::Dec::ProcessAndXorBlock(const byte *inBlock, const byte *xorBlock, byte *outBlock) const
{
    const RC5_WORD *sptr = sTable.end();
    RC5_WORD a, b;
 
    Block::Get(inBlock)(a)(b);
 
    for (unsigned i=0; i<r; i++)
    {
        sptr-=2;
        b = rotrMod(b-sptr[1], a) ^ a;
        a = rotrMod(a-sptr[0], b) ^ b;
    }
    b -= sTable[1];
    a -= sTable[0];
 
    Block::Put(xorBlock, outBlock)(a)(b);
}
 
NAMESPACE_END