idea.cpp

// idea.cpp - originally 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