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/*************************************************
* IDEA Source File *
* (C) 1999-2006 The Botan Project *
*************************************************/
#include <botan/idea.h>
#include <botan/bit_ops.h>
namespace Botan {
namespace {
/*************************************************
* Multiplication modulo 65537 *
*************************************************/
inline void mul(u16bit& a, u16bit b)
{
if(a && b)
{
u32bit temp = (u32bit)a * b;
a = (u16bit)(temp >> 16);
b = (u16bit)(temp & 0xFFFF);
a = (u16bit)(b - a + ((b < a) ? 1 : 0));
}
else
a = (u16bit)(1 - a - b);
}
}
/*************************************************
* IDEA Encryption *
*************************************************/
void IDEA::enc(const byte in[], byte out[]) const
{
u16bit X1 = make_u16bit(in[0], in[1]), X2 = make_u16bit(in[2], in[3]),
X3 = make_u16bit(in[4], in[5]), X4 = make_u16bit(in[6], in[7]);
for(u32bit j = 0; j != 8; ++j)
{
mul(X1, EK[6*j+0]);
X2 += EK[6*j+1];
X3 += EK[6*j+2];
mul(X4, EK[6*j+3]);
u16bit T0 = X3;
X3 ^= X1;
mul(X3, EK[6*j+4]);
u16bit T1 = X2;
X2 = (u16bit)((X2 ^ X4) + X3);
mul(X2, EK[6*j+5]);
X3 += X2;
X1 ^= X2;
X4 ^= X3;
X2 ^= T0;
X3 ^= T1;
}
mul(X1, EK[48]); X2 += EK[50]; X3 += EK[49]; mul(X4, EK[51]);
out[0] = get_byte(0, X1); out[1] = get_byte(1, X1);
out[2] = get_byte(0, X3); out[3] = get_byte(1, X3);
out[4] = get_byte(0, X2); out[5] = get_byte(1, X2);
out[6] = get_byte(0, X4); out[7] = get_byte(1, X4);
}
/*************************************************
* IDEA Decryption *
*************************************************/
void IDEA::dec(const byte in[], byte out[]) const
{
u16bit X1 = make_u16bit(in[0], in[1]), X2 = make_u16bit(in[2], in[3]),
X3 = make_u16bit(in[4], in[5]), X4 = make_u16bit(in[6], in[7]);
for(u32bit j = 0; j != 8; ++j)
{
mul(X1, DK[6*j+0]);
X2 += DK[6*j+1];
X3 += DK[6*j+2];
mul(X4, DK[6*j+3]);
u16bit T0 = X3;
X3 ^= X1;
mul(X3, DK[6*j+4]);
u16bit T1 = X2;
X2 = (u16bit)((X2 ^ X4) + X3);
mul(X2, DK[6*j+5]);
X3 += X2;
X1 ^= X2;
X4 ^= X3;
X2 ^= T0;
X3 ^= T1;
}
mul(X1, DK[48]); X2 += DK[50]; X3 += DK[49]; mul(X4, DK[51]);
out[0] = get_byte(0, X1); out[1] = get_byte(1, X1);
out[2] = get_byte(0, X3); out[3] = get_byte(1, X3);
out[4] = get_byte(0, X2); out[5] = get_byte(1, X2);
out[6] = get_byte(0, X4); out[7] = get_byte(1, X4);
}
/*************************************************
* Find multiplicative inverses modulo 65537 *
*************************************************/
u16bit IDEA::mul_inv(u16bit x)
{
if(x <= 1)
return x;
u16bit t0 = (u16bit)(65537 / x), t1 = 1, y = (u16bit)(65537 % x);
while(y != 1)
{
u16bit q = (u16bit)(x / y);
x %= y;
t1 += (u16bit)(q * t0);
if(x == 1)
return t1;
q = (u16bit)(y / x);
y %= x;
t0 += (u16bit)(q * t1);
}
return (u16bit)(1 - t0);
}
/*************************************************
* IDEA Key Schedule *
*************************************************/
void IDEA::key(const byte key[], u32bit)
{
for(u32bit j = 0; j != 8; ++j)
EK[j] = make_u16bit(key[2*j], key[2*j+1]);
for(u32bit j = 1, k = 8, offset = 0; k != 52; j %= 8, ++j, ++k)
{
EK[j+7+offset] = (u16bit)((EK[(j % 8) + offset] << 9) |
(EK[((j+1) % 8) + offset] >> 7));
offset += (j == 8) ? 8 : 0;
}
DK[51] = mul_inv(EK[3]);
DK[50] = (u16bit)-EK[2];
DK[49] = (u16bit)-EK[1];
DK[48] = mul_inv(EK[0]);
for(u32bit j = 1, k = 4, counter = 47; j != 8; ++j, k += 6)
{
DK[counter--] = EK[k+1];
DK[counter--] = EK[k];
DK[counter--] = mul_inv(EK[k+5]);
DK[counter--] = (u16bit)-EK[k+3];
DK[counter--] = (u16bit)-EK[k+4];
DK[counter--] = mul_inv(EK[k+2]);
}
DK[5] = EK[47];
DK[4] = EK[46];
DK[3] = mul_inv(EK[51]);
DK[2] = (u16bit)-EK[50];
DK[1] = (u16bit)-EK[49];
DK[0] = mul_inv(EK[48]);
}
}
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