twofish.cpp

// twofish.cpp - modified by Wei Dai from Matthew Skala's twofish.c
// The original code and all modifications are in the public domain.

#include "pch.h"
#include "twofish.h"
#include "misc.h"

NAMESPACE_BEGIN(CryptoPP)

// compute (c * x^4) mod (x^4 + (a + 1/a) * x^3 + a * x^2 + (a + 1/a) * x + 1)
// over GF(256)
static inline unsigned int Mod(unsigned int c)
{
        static const unsigned int modulus = 0x14d;
        unsigned int c2 = (c<<1) ^ ((c & 0x80) ? modulus : 0);
        unsigned int c1 = c2 ^ (c>>1) ^ ((c & 1) ? (modulus>>1) : 0);
        return c | (c1 << 8) | (c2 << 16) | (c1 << 24);
}

// compute RS(12,8) code with the above polynomial as generator
// this is equivalent to multiplying by the RS matrix
static word32 ReedSolomon(word32 high, word32 low)
{
        for (unsigned int i=0; i<8; i++)
        {
                high = Mod(high>>24) ^ (high<<8) ^ (low>>24);
                low <<= 8;
        }
        return high;
}

inline word32 Twofish::Base::h0(word32 x, const word32 *key, unsigned int kLen)
{
        x = x | (x<<8) | (x<<16) | (x<<24);
        switch(kLen)
        {
#define Q(a, b, c, d, t) q[a][GETBYTE(t,0)] ^ (q[b][GETBYTE(t,1)] << 8) ^ (q[c][GETBYTE(t,2)] << 16) ^ (q[d][GETBYTE(t,3)] << 24)
        case 4: x = Q(1, 0, 0, 1, x) ^ key[6];
        case 3: x = Q(1, 1, 0, 0, x) ^ key[4];
        case 2: x = Q(0, 1, 0, 1, x) ^ key[2];
                        x = Q(0, 0, 1, 1, x) ^ key[0];
        }
        return x;
}

inline word32 Twofish::Base::h(word32 x, const word32 *key, unsigned int kLen)
{
        x = h0(x, key, kLen);
        return mds[0][GETBYTE(x,0)] ^ mds[1][GETBYTE(x,1)] ^ mds[2][GETBYTE(x,2)] ^ mds[3][GETBYTE(x,3)];
}

void Twofish::Base::UncheckedSetKey(CipherDir dir, const byte *userKey, unsigned int keylength)
{
        AssertValidKeyLength(keylength);

        unsigned int len = (keylength <= 16 ? 2 : (keylength <= 24 ? 3 : 4));
        SecBlock<word32> key(len*2);
        GetUserKey(LITTLE_ENDIAN_ORDER, key.begin(), len*2, userKey, keylength);

        unsigned int i;
        for (i=0; i<40; i+=2)
        {
                word32 a = h(i, key, len);
                word32 b = rotlFixed(h(i+1, key+1, len), 8);
                m_k[i] = a+b;
                m_k[i+1] = rotlFixed(a+2*b, 9);
        }

        SecBlock<word32> svec(2*len);
        for (i=0; i<len; i++)
                svec[2*(len-i-1)] = ReedSolomon(key[2*i+1], key[2*i]);
        for (i=0; i<256; i++)
        {
                word32 t = h0(i, svec, len);
                m_s[0][i] = mds[0][GETBYTE(t, 0)];
                m_s[1][i] = mds[1][GETBYTE(t, 1)];
                m_s[2][i] = mds[2][GETBYTE(t, 2)];
                m_s[3][i] = mds[3][GETBYTE(t, 3)];
        }
}

#define G1(x) (m_s[0][GETBYTE(x,0)] ^ m_s[1][GETBYTE(x,1)] ^ m_s[2][GETBYTE(x,2)] ^ m_s[3][GETBYTE(x,3)])
#define G2(x) (m_s[0][GETBYTE(x,3)] ^ m_s[1][GETBYTE(x,0)] ^ m_s[2][GETBYTE(x,1)] ^ m_s[3][GETBYTE(x,2)])

#define ENCROUND(n, a, b, c, d) \
        x = G1 (a); y = G2 (b); \
        x += y; y += x + k[2 * (n) + 1]; \
        (c) ^= x + k[2 * (n)]; \
        (c) = rotrFixed(c, 1); \
        (d) = rotlFixed(d, 1) ^ y

#define ENCCYCLE(n) \
        ENCROUND (2 * (n), a, b, c, d); \
        ENCROUND (2 * (n) + 1, c, d, a, b)

#define DECROUND(n, a, b, c, d) \
        x = G1 (a); y = G2 (b); \
        x += y; y += x; \
        (d) ^= y + k[2 * (n) + 1]; \
        (d) = rotrFixed(d, 1); \
        (c) = rotlFixed(c, 1); \
        (c) ^= (x + k[2 * (n)])

#define DECCYCLE(n) \
        DECROUND (2 * (n) + 1, c, d, a, b); \
        DECROUND (2 * (n), a, b, c, d)

typedef BlockGetAndPut<word32, LittleEndian> Block;

void Twofish::Enc::ProcessAndXorBlock(const byte *inBlock, const byte *xorBlock, byte *outBlock) const
{
        word32 x, y, a, b, c, d;

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

        a ^= m_k[0];
        b ^= m_k[1];
        c ^= m_k[2];
        d ^= m_k[3];

        const word32 *k = m_k+8;
        ENCCYCLE (0);
        ENCCYCLE (1);
        ENCCYCLE (2);
        ENCCYCLE (3);
        ENCCYCLE (4);
        ENCCYCLE (5);
        ENCCYCLE (6);
        ENCCYCLE (7);

        c ^= m_k[4];
        d ^= m_k[5];
        a ^= m_k[6];
        b ^= m_k[7]; 

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

void Twofish::Dec::ProcessAndXorBlock(const byte *inBlock, const byte *xorBlock, byte *outBlock) const
{
        word32 x, y, a, b, c, d;

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

        c ^= m_k[4];
        d ^= m_k[5];
        a ^= m_k[6];
        b ^= m_k[7];

        const word32 *k = m_k+8;
        DECCYCLE (7);
        DECCYCLE (6);
        DECCYCLE (5);
        DECCYCLE (4);
        DECCYCLE (3);
        DECCYCLE (2);
        DECCYCLE (1);
        DECCYCLE (0);

        a ^= m_k[0];
        b ^= m_k[1];
        c ^= m_k[2];
        d ^= m_k[3];

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

NAMESPACE_END

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