/*************************************************
* 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]);
   }

}