cast128.cpp

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/*
* CAST-128
* (C) 1999-2007 Jack Lloyd
*
* Distributed under the terms of the Botan license
*/
 
#include <botan/cast128.h>
#include <botan/loadstor.h>
#include <botan/rotate.h>
 
namespace Botan {
 
namespace {
 
/*
* CAST-128 Round Type 1
*/
inline void R1(u32bit& L, u32bit R, u32bit MK, u32bit RK)
   {
   u32bit T = rotate_left(MK + R, RK);
   L ^= (CAST_SBOX1[get_byte(0, T)] ^ CAST_SBOX2[get_byte(1, T)]) -
         CAST_SBOX3[get_byte(2, T)] + CAST_SBOX4[get_byte(3, T)];
   }
 
/*
* CAST-128 Round Type 2
*/
inline void R2(u32bit& L, u32bit R, u32bit MK, u32bit RK)
   {
   u32bit T = rotate_left(MK ^ R, RK);
   L ^= (CAST_SBOX1[get_byte(0, T)]  - CAST_SBOX2[get_byte(1, T)] +
         CAST_SBOX3[get_byte(2, T)]) ^ CAST_SBOX4[get_byte(3, T)];
   }
 
/*
* CAST-128 Round Type 3
*/
inline void R3(u32bit& L, u32bit R, u32bit MK, u32bit RK)
   {
   u32bit T = rotate_left(MK - R, RK);
   L ^= ((CAST_SBOX1[get_byte(0, T)]  + CAST_SBOX2[get_byte(1, T)]) ^
          CAST_SBOX3[get_byte(2, T)]) - CAST_SBOX4[get_byte(3, T)];
   }
 
}
 
/*
* CAST-128 Encryption
*/
void CAST_128::encrypt_n(const byte in[], byte out[], size_t blocks) const
   {
   for(size_t i = 0; i != blocks; ++i)
      {
      u32bit L = load_be<u32bit>(in, 0);
      u32bit R = load_be<u32bit>(in, 1);
 
      R1(L, R, MK[ 0], RK[ 0]);
      R2(R, L, MK[ 1], RK[ 1]);
      R3(L, R, MK[ 2], RK[ 2]);
      R1(R, L, MK[ 3], RK[ 3]);
      R2(L, R, MK[ 4], RK[ 4]);
      R3(R, L, MK[ 5], RK[ 5]);
      R1(L, R, MK[ 6], RK[ 6]);
      R2(R, L, MK[ 7], RK[ 7]);
      R3(L, R, MK[ 8], RK[ 8]);
      R1(R, L, MK[ 9], RK[ 9]);
      R2(L, R, MK[10], RK[10]);
      R3(R, L, MK[11], RK[11]);
      R1(L, R, MK[12], RK[12]);
      R2(R, L, MK[13], RK[13]);
      R3(L, R, MK[14], RK[14]);
      R1(R, L, MK[15], RK[15]);
 
      store_be(out, R, L);
 
      in += BLOCK_SIZE;
      out += BLOCK_SIZE;
      }
   }
 
/*
* CAST-128 Decryption
*/
void CAST_128::decrypt_n(const byte in[], byte out[], size_t blocks) const
   {
   for(size_t i = 0; i != blocks; ++i)
      {
      u32bit L = load_be<u32bit>(in, 0);
      u32bit R = load_be<u32bit>(in, 1);
 
      R1(L, R, MK[15], RK[15]);
      R3(R, L, MK[14], RK[14]);
      R2(L, R, MK[13], RK[13]);
      R1(R, L, MK[12], RK[12]);
      R3(L, R, MK[11], RK[11]);
      R2(R, L, MK[10], RK[10]);
      R1(L, R, MK[ 9], RK[ 9]);
      R3(R, L, MK[ 8], RK[ 8]);
      R2(L, R, MK[ 7], RK[ 7]);
      R1(R, L, MK[ 6], RK[ 6]);
      R3(L, R, MK[ 5], RK[ 5]);
      R2(R, L, MK[ 4], RK[ 4]);
      R1(L, R, MK[ 3], RK[ 3]);
      R3(R, L, MK[ 2], RK[ 2]);
      R2(L, R, MK[ 1], RK[ 1]);
      R1(R, L, MK[ 0], RK[ 0]);
 
      store_be(out, R, L);
 
      in += BLOCK_SIZE;
      out += BLOCK_SIZE;
      }
   }
 
/*
* CAST-128 Key Schedule
*/
void CAST_128::key_schedule(const byte key[], size_t length)
   {
   clear();
   SecureVector<u32bit> X(4);
   for(size_t j = 0; j != length; ++j)
      X[j/4] = (X[j/4] << 8) + key[j];
 
   cast_ks(MK, X);
   cast_ks(RK, X);
 
   for(size_t j = 0; j != 16; ++j)
      RK[j] %= 32;
   }
 
/*
* S-Box Based Key Expansion
*/
void CAST_128::cast_ks(MemoryRegion<u32bit>& K,
                       MemoryRegion<u32bit>& X)
   {
   class ByteReader
      {
      public:
         byte operator()(size_t i) { return (X[i/4] >> (8*(3 - (i%4)))); }
         ByteReader(const u32bit* x) : X(x) {}
      private:
         const u32bit* X;
      };
 
   SecureVector<u32bit> Z(4);
   ByteReader x(&X[0]), z(&Z[0]);
 
   Z[0]  = X[0] ^ S5[x(13)] ^ S6[x(15)] ^ S7[x(12)] ^ S8[x(14)] ^ S7[x( 8)];
   Z[1]  = X[2] ^ S5[z( 0)] ^ S6[z( 2)] ^ S7[z( 1)] ^ S8[z( 3)] ^ S8[x(10)];
   Z[2]  = X[3] ^ S5[z( 7)] ^ S6[z( 6)] ^ S7[z( 5)] ^ S8[z( 4)] ^ S5[x( 9)];
   Z[3]  = X[1] ^ S5[z(10)] ^ S6[z( 9)] ^ S7[z(11)] ^ S8[z( 8)] ^ S6[x(11)];
   K[ 0] = S5[z( 8)] ^ S6[z( 9)] ^ S7[z( 7)] ^ S8[z( 6)] ^ S5[z( 2)];
   K[ 1] = S5[z(10)] ^ S6[z(11)] ^ S7[z( 5)] ^ S8[z( 4)] ^ S6[z( 6)];
   K[ 2] = S5[z(12)] ^ S6[z(13)] ^ S7[z( 3)] ^ S8[z( 2)] ^ S7[z( 9)];
   K[ 3] = S5[z(14)] ^ S6[z(15)] ^ S7[z( 1)] ^ S8[z( 0)] ^ S8[z(12)];
   X[0]  = Z[2] ^ S5[z( 5)] ^ S6[z( 7)] ^ S7[z( 4)] ^ S8[z( 6)] ^ S7[z( 0)];
   X[1]  = Z[0] ^ S5[x( 0)] ^ S6[x( 2)] ^ S7[x( 1)] ^ S8[x( 3)] ^ S8[z( 2)];
   X[2]  = Z[1] ^ S5[x( 7)] ^ S6[x( 6)] ^ S7[x( 5)] ^ S8[x( 4)] ^ S5[z( 1)];
   X[3]  = Z[3] ^ S5[x(10)] ^ S6[x( 9)] ^ S7[x(11)] ^ S8[x( 8)] ^ S6[z( 3)];
   K[ 4] = S5[x( 3)] ^ S6[x( 2)] ^ S7[x(12)] ^ S8[x(13)] ^ S5[x( 8)];
   K[ 5] = S5[x( 1)] ^ S6[x( 0)] ^ S7[x(14)] ^ S8[x(15)] ^ S6[x(13)];
   K[ 6] = S5[x( 7)] ^ S6[x( 6)] ^ S7[x( 8)] ^ S8[x( 9)] ^ S7[x( 3)];
   K[ 7] = S5[x( 5)] ^ S6[x( 4)] ^ S7[x(10)] ^ S8[x(11)] ^ S8[x( 7)];
   Z[0]  = X[0] ^ S5[x(13)] ^ S6[x(15)] ^ S7[x(12)] ^ S8[x(14)] ^ S7[x( 8)];
   Z[1]  = X[2] ^ S5[z( 0)] ^ S6[z( 2)] ^ S7[z( 1)] ^ S8[z( 3)] ^ S8[x(10)];
   Z[2]  = X[3] ^ S5[z( 7)] ^ S6[z( 6)] ^ S7[z( 5)] ^ S8[z( 4)] ^ S5[x( 9)];
   Z[3]  = X[1] ^ S5[z(10)] ^ S6[z( 9)] ^ S7[z(11)] ^ S8[z( 8)] ^ S6[x(11)];
   K[ 8] = S5[z( 3)] ^ S6[z( 2)] ^ S7[z(12)] ^ S8[z(13)] ^ S5[z( 9)];
   K[ 9] = S5[z( 1)] ^ S6[z( 0)] ^ S7[z(14)] ^ S8[z(15)] ^ S6[z(12)];
   K[10] = S5[z( 7)] ^ S6[z( 6)] ^ S7[z( 8)] ^ S8[z( 9)] ^ S7[z( 2)];
   K[11] = S5[z( 5)] ^ S6[z( 4)] ^ S7[z(10)] ^ S8[z(11)] ^ S8[z( 6)];
   X[0]  = Z[2] ^ S5[z( 5)] ^ S6[z( 7)] ^ S7[z( 4)] ^ S8[z( 6)] ^ S7[z( 0)];
   X[1]  = Z[0] ^ S5[x( 0)] ^ S6[x( 2)] ^ S7[x( 1)] ^ S8[x( 3)] ^ S8[z( 2)];
   X[2]  = Z[1] ^ S5[x( 7)] ^ S6[x( 6)] ^ S7[x( 5)] ^ S8[x( 4)] ^ S5[z( 1)];
   X[3]  = Z[3] ^ S5[x(10)] ^ S6[x( 9)] ^ S7[x(11)] ^ S8[x( 8)] ^ S6[z( 3)];
   K[12] = S5[x( 8)] ^ S6[x( 9)] ^ S7[x( 7)] ^ S8[x( 6)] ^ S5[x( 3)];
   K[13] = S5[x(10)] ^ S6[x(11)] ^ S7[x( 5)] ^ S8[x( 4)] ^ S6[x( 7)];
   K[14] = S5[x(12)] ^ S6[x(13)] ^ S7[x( 3)] ^ S8[x( 2)] ^ S7[x( 8)];
   K[15] = S5[x(14)] ^ S6[x(15)] ^ S7[x( 1)] ^ S8[x( 0)] ^ S8[x(13)];
   }
 
}