cast.c

/*
 * $Id$
 *
 *	CAST-128 in C
 *	Written by Steve Reid <sreid@sea-to-sky.net>
 *	100% Public Domain - no warranty
 *	Released 1997.10.11
 *
 *	CAST-128 is documented in
 *	C. Adams, "The CAST-128 Encryption Algorithm", RFC 2144.
 *
 */

/* Adapted to the pike cryptographic toolkit by Niels Mller */

/* Selftest added by J.H.M. Dassen (Ray) <jdassen@wi.LeidenUniv.nl>.
 * Released into the public domain. */

#include <assert.h>

#include <cast.h>

#define u8 UINT8
#define u32 UINT32

#include "cast_sboxes.h"

/* Macros to access 8-bit bytes out of a 32-bit word */
#define U8a(x) ( (u8) (x>>24) )
#define U8b(x) ( (u8) ((x>>16)&255) )
#define U8c(x) ( (u8) ((x>>8)&255) )
#define U8d(x) ( (u8) ((x)&255) )

/* Circular left shift */
#define ROL(x, n) ( ((x)<<(n)) | ((x)>>(32-(n))) )

/* CAST-128 uses three different round functions */
#define F1(l, r, i) \
	t = ROL(key->xkey[i] + r, key->xkey[i+16]); \
	l ^= ((cast_sbox1[U8a(t)] ^ cast_sbox2[U8b(t)]) \
	 - cast_sbox3[U8c(t)]) + cast_sbox4[U8d(t)];
#define F2(l, r, i) \
	t = ROL(key->xkey[i] ^ r, key->xkey[i+16]); \
	l ^= ((cast_sbox1[U8a(t)] - cast_sbox2[U8b(t)]) \
	 + cast_sbox3[U8c(t)]) ^ cast_sbox4[U8d(t)];
#define F3(l, r, i) \
	t = ROL(key->xkey[i] - r, key->xkey[i+16]); \
	l ^= ((cast_sbox1[U8a(t)] + cast_sbox2[U8b(t)]) \
	 ^ cast_sbox3[U8c(t)]) - cast_sbox4[U8d(t)];


/***** Encryption Function *****/

void cast_encrypt(struct cast_key *key, const u8 * const inblock, u8 *outblock)
{
  u32 t, l, r;

  /* Get inblock into l,r */
  l = ((u32)inblock[0] << 24) | ((u32)inblock[1] << 16)
    | ((u32)inblock[2] << 8) | (u32)inblock[3];
  r = ((u32)inblock[4] << 24) | ((u32)inblock[5] << 16)
    | ((u32)inblock[6] << 8) | (u32)inblock[7];
  /* Do the work */
  F1(l, r,  0);
  F2(r, l,  1);
  F3(l, r,  2);
  F1(r, l,  3);
  F2(l, r,  4);
  F3(r, l,  5);
  F1(l, r,  6);
  F2(r, l,  7);
  F3(l, r,  8);
  F1(r, l,  9);
  F2(l, r, 10);
  F3(r, l, 11);
  /* Only do full 16 rounds if key length > 80 bits */
  if (key->rounds > 12) {
    F1(l, r, 12);
    F2(r, l, 13);
    F3(l, r, 14);
    F1(r, l, 15);
  }
  /* Put l,r into outblock */
  outblock[0] = U8a(r);
  outblock[1] = U8b(r);
  outblock[2] = U8c(r);
  outblock[3] = U8d(r);
  outblock[4] = U8a(l);
  outblock[5] = U8b(l);
  outblock[6] = U8c(l);
  outblock[7] = U8d(l);
  /* Wipe clean */
  t = l = r = 0;
}


/***** Decryption Function *****/

void cast_decrypt(struct cast_key *key, const u8 * const inblock, u8 *outblock)
{
  u32 t, l, r;

  /* Get inblock into l,r */
  r = ((u32)inblock[0] << 24) | ((u32)inblock[1] << 16)
    | ((u32)inblock[2] << 8) | (u32)inblock[3];
  l = ((u32)inblock[4] << 24) | ((u32)inblock[5] << 16)
    | ((u32)inblock[6] << 8) | (u32)inblock[7];
  /* Do the work */
  /* Only do full 16 rounds if key length > 80 bits */
  if (key->rounds > 12) {
    F1(r, l, 15);
    F3(l, r, 14);
    F2(r, l, 13);
    F1(l, r, 12);
  }
  F3(r, l, 11);
  F2(l, r, 10);
  F1(r, l,  9);
  F3(l, r,  8);
  F2(r, l,  7);
  F1(l, r,  6);
  F3(r, l,  5);
  F2(l, r,  4);
  F1(r, l,  3);
  F3(l, r,  2);
  F2(r, l,  1);
  F1(l, r,  0);
  /* Put l,r into outblock */
  outblock[0] = U8a(l);
  outblock[1] = U8b(l);
  outblock[2] = U8c(l);
  outblock[3] = U8d(l);
  outblock[4] = U8a(r);
  outblock[5] = U8b(r);
  outblock[6] = U8c(r);
  outblock[7] = U8d(r);
  /* Wipe clean */
  t = l = r = 0;
}


/* Sanity check using the test vectors from
 * B.1. Single Plaintext-Key-Ciphertext Sets, RFC 2144
 */
int cast_selftest(void)
{
  u8 testkey128[16] = {
    0x01, 0x23, 0x45, 0x67, 0x12, 0x34, 0x56, 0x78,
    0x23, 0x45, 0x67, 0x89, 0x34, 0x56, 0x78, 0x9A
  };
  u8 plaintext128[8] = {
    0x01, 0x23, 0x45, 0x67, 0x89, 0xAB, 0xCD, 0xEF
  };
  u8 ciphertext128[8] = {
    0x23, 0x8B, 0x4F, 0xE5, 0x84, 0x7E, 0x44, 0xB2
  };

  u8 testkey80[10] = {
    0x01, 0x23, 0x45, 0x67, 0x12, 0x34, 0x56, 0x78,
    0x23, 0x45
  };
  u8 plaintext80[8] = {
    0x01, 0x23, 0x45, 0x67, 0x89, 0xAB, 0xCD, 0xEF
  };
  u8 ciphertext80[8] = {
    0xEB, 0x6A, 0x71, 0x1A, 0x2C, 0x02, 0x27, 0x1B
  };

  u8 testkey40[5] = {
    0x01, 0x23, 0x45, 0x67, 0x12
  };
  u8 plaintext40[8] = {
    0x01, 0x23, 0x45, 0x67, 0x89, 0xAB, 0xCD, 0xEF
  };
  u8 ciphertext40[8] = {
    0x7A, 0xC8, 0x16, 0xD1, 0x6E, 0x9B, 0x30, 0x2E
  };

  struct cast_key context;
  u8 ciphertext[8];

  cast_setkey(&context, testkey128, 16);
  cast_encrypt(&context, plaintext128, ciphertext);
  if (memcmp(ciphertext, ciphertext128, 8)) {
        return 0;
  }
  cast_setkey(&context, testkey80, 10);
  cast_encrypt(&context, plaintext80, ciphertext);
  if (memcmp(ciphertext, ciphertext80, 8)) {
        return 0;
  }
  cast_setkey(&context, testkey40, 5);
  cast_encrypt(&context, plaintext40, ciphertext);
  if (memcmp(ciphertext, ciphertext40, 8)) {
        return 0;
  }
  return 1;
}


/***** Key Schedule *****/

void cast_setkey(struct cast_key *key, const u8 * const rawkey, unsigned keybytes)
{
  u32 t[4], z[4], x[4];
  unsigned i;

#ifndef NDEBUG
  static int initialized = 0;

  if (!initialized)
    {
      initialized = 1;
      assert(cast_selftest());
    }
#endif

  /* Set number of rounds to 12 or 16, depending on key length */
  key->rounds = (keybytes <= CAST_SMALL_KEY)
    ? CAST_SMALL_ROUNDS : CAST_FULL_ROUNDS;

  /* Copy key to workspace x */
  for (i = 0; i < 4; i++) {
    x[i] = 0;
    if ((i*4+0) < keybytes) x[i] = (u32)rawkey[i*4+0] << 24;
    if ((i*4+1) < keybytes) x[i] |= (u32)rawkey[i*4+1] << 16;
    if ((i*4+2) < keybytes) x[i] |= (u32)rawkey[i*4+2] << 8;
    if ((i*4+3) < keybytes) x[i] |= (u32)rawkey[i*4+3];
  }
  /* Generate 32 subkeys, four at a time */
  for (i = 0; i < 32; i+=4) {
    switch (i & 4) {
    case 0:
      t[0] = z[0] = x[0] ^ cast_sbox5[U8b(x[3])]
	^ cast_sbox6[U8d(x[3])] ^ cast_sbox7[U8a(x[3])]
	^ cast_sbox8[U8c(x[3])] ^ cast_sbox7[U8a(x[2])];
      t[1] = z[1] = x[2] ^ cast_sbox5[U8a(z[0])]
	^ cast_sbox6[U8c(z[0])] ^ cast_sbox7[U8b(z[0])]
	^ cast_sbox8[U8d(z[0])] ^ cast_sbox8[U8c(x[2])];
      t[2] = z[2] = x[3] ^ cast_sbox5[U8d(z[1])]
	^ cast_sbox6[U8c(z[1])] ^ cast_sbox7[U8b(z[1])]
	^ cast_sbox8[U8a(z[1])] ^ cast_sbox5[U8b(x[2])];
      t[3] = z[3] = x[1] ^ cast_sbox5[U8c(z[2])] ^
	cast_sbox6[U8b(z[2])] ^ cast_sbox7[U8d(z[2])]
	^ cast_sbox8[U8a(z[2])] ^ cast_sbox6[U8d(x[2])];
      break;
    case 4:
      t[0] = x[0] = z[2] ^ cast_sbox5[U8b(z[1])]
	^ cast_sbox6[U8d(z[1])] ^ cast_sbox7[U8a(z[1])]
	^ cast_sbox8[U8c(z[1])] ^ cast_sbox7[U8a(z[0])];
      t[1] = x[1] = z[0] ^ cast_sbox5[U8a(x[0])]
	^ cast_sbox6[U8c(x[0])] ^ cast_sbox7[U8b(x[0])]
	^ cast_sbox8[U8d(x[0])] ^ cast_sbox8[U8c(z[0])];
      t[2] = x[2] = z[1] ^ cast_sbox5[U8d(x[1])]
	^ cast_sbox6[U8c(x[1])] ^ cast_sbox7[U8b(x[1])]
	^ cast_sbox8[U8a(x[1])] ^ cast_sbox5[U8b(z[0])];
      t[3] = x[3] = z[3] ^ cast_sbox5[U8c(x[2])]
	^ cast_sbox6[U8b(x[2])] ^ cast_sbox7[U8d(x[2])]
	^ cast_sbox8[U8a(x[2])] ^ cast_sbox6[U8d(z[0])];
      break;
    }
    switch (i & 12) {
    case 0:
    case 12:
      key->xkey[i+0] = cast_sbox5[U8a(t[2])] ^ cast_sbox6[U8b(t[2])]
	^ cast_sbox7[U8d(t[1])] ^ cast_sbox8[U8c(t[1])];
      key->xkey[i+1] = cast_sbox5[U8c(t[2])] ^ cast_sbox6[U8d(t[2])]
	^ cast_sbox7[U8b(t[1])] ^ cast_sbox8[U8a(t[1])];
      key->xkey[i+2] = cast_sbox5[U8a(t[3])] ^ cast_sbox6[U8b(t[3])]
	^ cast_sbox7[U8d(t[0])] ^ cast_sbox8[U8c(t[0])];
      key->xkey[i+3] = cast_sbox5[U8c(t[3])] ^ cast_sbox6[U8d(t[3])]
	^ cast_sbox7[U8b(t[0])] ^ cast_sbox8[U8a(t[0])];
      break;
    case 4:
    case 8:
      key->xkey[i+0] = cast_sbox5[U8d(t[0])] ^ cast_sbox6[U8c(t[0])]
	^ cast_sbox7[U8a(t[3])] ^ cast_sbox8[U8b(t[3])];
      key->xkey[i+1] = cast_sbox5[U8b(t[0])] ^ cast_sbox6[U8a(t[0])]
	^ cast_sbox7[U8c(t[3])] ^ cast_sbox8[U8d(t[3])];
      key->xkey[i+2] = cast_sbox5[U8d(t[1])] ^ cast_sbox6[U8c(t[1])]
	^ cast_sbox7[U8a(t[2])] ^ cast_sbox8[U8b(t[2])];
      key->xkey[i+3] = cast_sbox5[U8b(t[1])] ^ cast_sbox6[U8a(t[1])]
	^ cast_sbox7[U8c(t[2])] ^ cast_sbox8[U8d(t[2])];
      break;
    }
    switch (i & 12) {
    case 0:
      key->xkey[i+0] ^= cast_sbox5[U8c(z[0])];
      key->xkey[i+1] ^= cast_sbox6[U8c(z[1])];
      key->xkey[i+2] ^= cast_sbox7[U8b(z[2])];
      key->xkey[i+3] ^= cast_sbox8[U8a(z[3])];
      break;
    case 4:
      key->xkey[i+0] ^= cast_sbox5[U8a(x[2])];
      key->xkey[i+1] ^= cast_sbox6[U8b(x[3])];
      key->xkey[i+2] ^= cast_sbox7[U8d(x[0])];
      key->xkey[i+3] ^= cast_sbox8[U8d(x[1])];
      break;
    case 8:
      key->xkey[i+0] ^= cast_sbox5[U8b(z[2])];
      key->xkey[i+1] ^= cast_sbox6[U8a(z[3])];
      key->xkey[i+2] ^= cast_sbox7[U8c(z[0])];
      key->xkey[i+3] ^= cast_sbox8[U8c(z[1])];
      break;
    case 12:
      key->xkey[i+0] ^= cast_sbox5[U8d(x[0])];
      key->xkey[i+1] ^= cast_sbox6[U8d(x[1])];
      key->xkey[i+2] ^= cast_sbox7[U8a(x[2])];
      key->xkey[i+3] ^= cast_sbox8[U8b(x[3])];
      break;
    }
    if (i >= 16) {
      key->xkey[i+0] &= 31;
      key->xkey[i+1] &= 31;
      key->xkey[i+2] &= 31;
      key->xkey[i+3] &= 31;
    }
  }
  /* Wipe clean */
  for (i = 0; i < 4; i++) {
    t[i] = x[i] = z[i] = 0;
  }
}

/* Made in Canada */