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/*************************************************
* IDEA Source File *
* (C) 1999-2008 The Botan Project *
*************************************************/
#include <botan/idea.h>
#include <botan/loadstor.h>
namespace Botan {
namespace {
/*************************************************
* Multiplication modulo 65537 *
*************************************************/
inline u16bit mul(u16bit x, u16bit y)
{
if(x && y)
{
u32bit T = static_cast<u32bit>(x) * y;
x = static_cast<u16bit>(T >> 16);
y = static_cast<u16bit>(T & 0xFFFF);
return static_cast<u16bit>(y - x + ((y < x) ? 1 : 0));
}
else
return static_cast<u16bit>(1 - x - y);
}
/*************************************************
* Find multiplicative inverses modulo 65537 *
*************************************************/
u16bit mul_inv(u16bit x)
{
if(x <= 1)
return x;
u16bit t0 = static_cast<u16bit>(65537 / x), t1 = 1;
u16bit y = static_cast<u16bit>(65537 % x);
while(y != 1)
{
u16bit q = x / y;
x %= y;
t1 += q * t0;
if(x == 1)
return t1;
q = y / x;
y %= x;
t0 += q * t1;
}
return (1 - t0);
}
}
/*************************************************
* IDEA Encryption *
*************************************************/
void IDEA::enc(const byte in[], byte out[]) const
{
u16bit X1 = load_be<u16bit>(in, 0);
u16bit X2 = load_be<u16bit>(in, 1);
u16bit X3 = load_be<u16bit>(in, 2);
u16bit X4 = load_be<u16bit>(in, 3);
for(u32bit j = 0; j != 8; ++j)
{
X1 = mul(X1, EK[6*j+0]);
X2 += EK[6*j+1];
X3 += EK[6*j+2];
X4 = mul(X4, EK[6*j+3]);
u16bit T0 = X3;
X3 = mul(X3 ^ X1, EK[6*j+4]);
u16bit T1 = X2;
X2 = mul((X2 ^ X4) + X3, EK[6*j+5]);
X3 += X2;
X1 ^= X2;
X4 ^= X3;
X2 ^= T0;
X3 ^= T1;
}
X1 = mul(X1, EK[48]);
X2 += EK[50];
X3 += EK[49];
X4 = mul(X4, EK[51]);
store_be(out, X1, X3, X2, X4);
}
/*************************************************
* IDEA Decryption *
*************************************************/
void IDEA::dec(const byte in[], byte out[]) const
{
u16bit X1 = load_be<u16bit>(in, 0);
u16bit X2 = load_be<u16bit>(in, 1);
u16bit X3 = load_be<u16bit>(in, 2);
u16bit X4 = load_be<u16bit>(in, 3);
for(u32bit j = 0; j != 8; ++j)
{
X1 = mul(X1, DK[6*j+0]);
X2 += DK[6*j+1];
X3 += DK[6*j+2];
X4 = mul(X4, DK[6*j+3]);
u16bit T0 = X3;
X3 = mul(X3 ^ X1, DK[6*j+4]);
u16bit T1 = X2;
X2 = mul((X2 ^ X4) + X3, DK[6*j+5]);
X3 += X2;
X1 ^= X2;
X4 ^= X3;
X2 ^= T0;
X3 ^= T1;
}
X1 = mul(X1, DK[48]);
X2 += DK[50];
X3 += DK[49];
X4 = mul(X4, DK[51]);
store_be(out, X1, X3, X2, X4);
}
/*************************************************
* IDEA Key Schedule *
*************************************************/
void IDEA::key(const byte key[], u32bit)
{
for(u32bit j = 0; j != 8; ++j)
EK[j] = load_be<u16bit>(key, j);
for(u32bit j = 1, k = 8, offset = 0; k != 52; j %= 8, ++j, ++k)
{
EK[j+7+offset] = static_cast<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] = -EK[2];
DK[49] = -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--] = -EK[k+3];
DK[counter--] = -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] = -EK[50];
DK[1] = -EK[49];
DK[0] = mul_inv(EK[48]);
}
}
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