rc5.cpp

// rc5.cpp - written and placed in the public domain by Wei Dai

#include "pch.h"
#include "rc5.h"
#include "misc.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()] = rotlFixed((sTable[h % sTable.size()] + a + b), 3);
                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

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