rc6.cpp

// rc6.cpp - written and placed in the public domain by Sean Woods
// based on Wei Dai's RC5 code.

#include "pch.h"
#include "rc6.h"
#include "misc.h"

NAMESPACE_BEGIN(CryptoPP)

void RC6::Base::UncheckedSetKey(const byte *k, unsigned int keylen, const NameValuePairs &params)
{
        AssertValidKeyLength(keylen);

        r = GetRoundsAndThrowIfInvalid(params, this);
        sTable.New(2*(r+2));

        static const RC6_WORD MAGIC_P = 0xb7e15163L;    // magic constant P for wordsize
        static const RC6_WORD MAGIC_Q = 0x9e3779b9L;    // magic constant Q for wordsize
        static const int U=sizeof(RC6_WORD);

        const unsigned int c = STDMAX((keylen+U-1)/U, 1U);      // RC6 paper says c=1 if keylen==0
        SecBlock<RC6_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;

        RC6_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<RC6::RC6_WORD, LittleEndian> Block;

void RC6::Enc::ProcessAndXorBlock(const byte *inBlock, const byte *xorBlock, byte *outBlock) const
{
        const RC6_WORD *sptr = sTable;
        RC6_WORD a, b, c, d, t, u;

        Block::Get(inBlock)(a)(b)(c)(d);
        b += sptr[0];
        d += sptr[1];
        sptr += 2;

        for(unsigned i=0; i<r; i++)
        {
                t = rotlFixed(b*(2*b+1), 5);
                u = rotlFixed(d*(2*d+1), 5);
                a = rotlMod(a^t,u) + sptr[0];
                c = rotlMod(c^u,t) + sptr[1];
                t = a; a = b; b = c; c = d; d = t;
                sptr += 2;
        }

        a += sptr[0];
        c += sptr[1];

        Block::Put(xorBlock, outBlock)(a)(b)(c)(d);
}

void RC6::Dec::ProcessAndXorBlock(const byte *inBlock, const byte *xorBlock, byte *outBlock) const
{
        const RC6_WORD *sptr = sTable.end();
        RC6_WORD a, b, c, d, t, u;

        Block::Get(inBlock)(a)(b)(c)(d);

        sptr -= 2;
        c -= sptr[1];
        a -= sptr[0];

        for (unsigned i=0; i < r; i++)
        {
                sptr -= 2;
                t = a; a = d; d = c; c = b; b = t;
                u = rotlFixed(d*(2*d+1), 5);
                t = rotlFixed(b*(2*b+1), 5);
                c = rotrMod(c-sptr[1], t) ^ u;
                a = rotrMod(a-sptr[0], u) ^ t;
        }

        sptr -= 2;
        d -= sTable[1];
        b -= sTable[0];

        Block::Put(xorBlock, outBlock)(a)(b)(c)(d);
}

NAMESPACE_END

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