idea.cpp

Go to the documentation of this file.

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

#include "pch.h"
#include "idea.h"
#include "misc.h"
#include "secblock.h"

NAMESPACE_BEGIN(CryptoPP)

static const int IDEA_KEYLEN=(6*IDEA::ROUNDS+4);  // key schedule length in # of word16s

#define low16(x) ((x)&0xffff)   // compiler should be able to optimize this away if word is 16 bits
#define high16(x) ((x)>>16)

CRYPTOPP_COMPILE_ASSERT(sizeof(IDEA::Word) >= 2);

// should use an inline function but macros are still faster in MSVC 4.0
#define DirectMUL(a,b)                                  \
{                                                                               \
        word32 p=(word32)low16(a)*b;            \
                                                                                \
        if (p)                                                          \
        {                                                                       \
                p = low16(p) - high16(p);               \
                a = (IDEA::Word)p - (IDEA::Word)high16(p);      \
        }                                                                       \
        else                                                            \
                a = 1-a-b;                                              \
}

#ifdef IDEA_LARGECACHE
volatile bool IDEA::Base::tablesBuilt = false;
word16 IDEA::Base::log[0x10000];
word16 IDEA::Base::antilog[0x10000];

void IDEA::Base::BuildLogTables()
{
        if (tablesBuilt)
                return;
        else
        {
                tablesBuilt = true;

                IDEA::Word x=1;
                word32 i;

                for (i=0; i<0x10000; i++)
                {
                        antilog[i] = (word16)x;
                        DirectMUL(x, 3);
                }

                for (i=0; i<0x10000; i++)
                        log[antilog[i]] = (word16)i;
        }
}

void IDEA::Base::LookupKeyLogs()
{
        IDEA::Word* Z=key;
        int r=ROUNDS;
        do
        {
                Z[0] = log[Z[0]];
                Z[3] = log[Z[3]];
                Z[4] = log[Z[4]];
                Z[5] = log[Z[5]];
                Z+=6;
        } while (--r);
        Z[0] = log[Z[0]];
        Z[3] = log[Z[3]];
}

inline void IDEA::Base::LookupMUL(IDEA::Word &a, IDEA::Word b)
{
        a = antilog[low16(log[low16(a)]+b)];
}
#endif // IDEA_LARGECACHE

void IDEA::Base::UncheckedSetKey(const byte *userKey, unsigned int length, const NameValuePairs &)
{
        AssertValidKeyLength(length);

#ifdef IDEA_LARGECACHE
        BuildLogTables();
#endif

        EnKey(userKey);

        if (!IsForwardTransformation())
                DeKey();

#ifdef IDEA_LARGECACHE
        LookupKeyLogs();
#endif
}

void IDEA::Base::EnKey (const byte *userKey)
{
        unsigned int i;

        for (i=0; i<8; i++)
                m_key[i] = ((IDEA::Word)userKey[2*i]<<8) | userKey[2*i+1];

        for (; i<IDEA_KEYLEN; i++)
        {
                unsigned int j = RoundDownToMultipleOf(i,8U)-8;
                m_key[i] = low16((m_key[j+(i+1)%8] << 9) | (m_key[j+(i+2)%8] >> 7));
        }
}

static IDEA::Word MulInv(IDEA::Word x)
{
        IDEA::Word y=x;
        for (unsigned i=0; i<15; i++)
        {
                DirectMUL(y,low16(y));
                DirectMUL(y,x);
        }
        return low16(y);
}

static inline IDEA::Word AddInv(IDEA::Word x)
{
        return low16(0-x);
}

void IDEA::Base::DeKey()
{
        FixedSizeSecBlock<IDEA::Word, 6*ROUNDS+4> tempkey;
        size_t i;

        for (i=0; i<ROUNDS; i++)
        {
                tempkey[i*6+0] = MulInv(m_key[(ROUNDS-i)*6+0]);
                tempkey[i*6+1] = AddInv(m_key[(ROUNDS-i)*6+1+(i>0)]);
                tempkey[i*6+2] = AddInv(m_key[(ROUNDS-i)*6+2-(i>0)]);
                tempkey[i*6+3] = MulInv(m_key[(ROUNDS-i)*6+3]);
                tempkey[i*6+4] =        m_key[(ROUNDS-1-i)*6+4];
                tempkey[i*6+5] =        m_key[(ROUNDS-1-i)*6+5];
        }

        tempkey[i*6+0] = MulInv(m_key[(ROUNDS-i)*6+0]);
        tempkey[i*6+1] = AddInv(m_key[(ROUNDS-i)*6+1]);
        tempkey[i*6+2] = AddInv(m_key[(ROUNDS-i)*6+2]);
        tempkey[i*6+3] = MulInv(m_key[(ROUNDS-i)*6+3]);

        m_key = tempkey;
}

#ifdef IDEA_LARGECACHE
#define MUL(a,b) LookupMUL(a,b)
#else
#define MUL(a,b) DirectMUL(a,b)
#endif

void IDEA::Base::ProcessAndXorBlock(const byte *inBlock, const byte *xorBlock, byte *outBlock) const
{
        typedef BlockGetAndPut<word16, BigEndian> Block;

        const IDEA::Word *key = m_key;
        IDEA::Word x0,x1,x2,x3,t0,t1;
        Block::Get(inBlock)(x0)(x1)(x2)(x3);

        for (unsigned int i=0; i<ROUNDS; i++)
        {
                MUL(x0, key[i*6+0]);
                x1 += key[i*6+1];
                x2 += key[i*6+2];
                MUL(x3, key[i*6+3]);
                t0 = x0^x2;
                MUL(t0, key[i*6+4]);
                t1 = t0 + (x1^x3);
                MUL(t1, key[i*6+5]);
                t0 += t1;
                x0 ^= t1;
                x3 ^= t0;
                t0 ^= x1;
                x1 = x2^t1;
                x2 = t0;
        }

        MUL(x0, key[ROUNDS*6+0]);
        x2 += key[ROUNDS*6+1];
        x1 += key[ROUNDS*6+2];
        MUL(x3, key[ROUNDS*6+3]);

        Block::Put(xorBlock, outBlock)(x0)(x2)(x1)(x3);
}

NAMESPACE_END