arctwo.c

/* arctwo.c
 *
 * The cipher described in rfc2268; aka Ron's Cipher 2.
 */
   
/* nettle, low-level cryptographics library
 *
 * Copyright (C) 2004 Simon Josefsson
 * Copyright (C) 2003 Nikos Mavroyanopoulos
 * Copyright (C) 2004 Free Software Foundation, Inc.
 * Copyright (C) 2004 Niels Mller
 *
 * The nettle library is free software; you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as published by
 * the Free Software Foundation; either version 2.1 of the License, or (at your
 * option) any later version.
 *
 * The nettle library is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
 * or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
 * License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with the nettle library; see the file COPYING.LIB.  If not, write to
 * the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
 * MA 02111-1307, USA.
 */

/* This implementation was written by Nikos Mavroyanopoulos for GNUTLS
 * as a Libgcrypt module (gnutls/lib/x509/rc2.c) and later adapted for
 * direct use by Libgcrypt by Werner Koch and later adapted for direct
 * use by Nettle by Simon Josefsson and Niels Mller.
 *
 * The implementation here is based on Peter Gutmann's RRC.2 paper and
 * RFC 2268.
 */

#if HAVE_CONFIG_H
# include "config.h"
#endif

#include <assert.h>

#include "arctwo.h"

#include "macros.h"

static const uint8_t arctwo_sbox[] = {
  0xd9, 0x78, 0xf9, 0xc4, 0x19, 0xdd, 0xb5, 0xed,
  0x28, 0xe9, 0xfd, 0x79, 0x4a, 0xa0, 0xd8, 0x9d,
  0xc6, 0x7e, 0x37, 0x83, 0x2b, 0x76, 0x53, 0x8e,
  0x62, 0x4c, 0x64, 0x88, 0x44, 0x8b, 0xfb, 0xa2,
  0x17, 0x9a, 0x59, 0xf5, 0x87, 0xb3, 0x4f, 0x13,
  0x61, 0x45, 0x6d, 0x8d, 0x09, 0x81, 0x7d, 0x32,
  0xbd, 0x8f, 0x40, 0xeb, 0x86, 0xb7, 0x7b, 0x0b,
  0xf0, 0x95, 0x21, 0x22, 0x5c, 0x6b, 0x4e, 0x82,
  0x54, 0xd6, 0x65, 0x93, 0xce, 0x60, 0xb2, 0x1c,
  0x73, 0x56, 0xc0, 0x14, 0xa7, 0x8c, 0xf1, 0xdc,
  0x12, 0x75, 0xca, 0x1f, 0x3b, 0xbe, 0xe4, 0xd1,
  0x42, 0x3d, 0xd4, 0x30, 0xa3, 0x3c, 0xb6, 0x26,
  0x6f, 0xbf, 0x0e, 0xda, 0x46, 0x69, 0x07, 0x57,
  0x27, 0xf2, 0x1d, 0x9b, 0xbc, 0x94, 0x43, 0x03,
  0xf8, 0x11, 0xc7, 0xf6, 0x90, 0xef, 0x3e, 0xe7,
  0x06, 0xc3, 0xd5, 0x2f, 0xc8, 0x66, 0x1e, 0xd7,
  0x08, 0xe8, 0xea, 0xde, 0x80, 0x52, 0xee, 0xf7,
  0x84, 0xaa, 0x72, 0xac, 0x35, 0x4d, 0x6a, 0x2a,
  0x96, 0x1a, 0xd2, 0x71, 0x5a, 0x15, 0x49, 0x74,
  0x4b, 0x9f, 0xd0, 0x5e, 0x04, 0x18, 0xa4, 0xec,
  0xc2, 0xe0, 0x41, 0x6e, 0x0f, 0x51, 0xcb, 0xcc,
  0x24, 0x91, 0xaf, 0x50, 0xa1, 0xf4, 0x70, 0x39,
  0x99, 0x7c, 0x3a, 0x85, 0x23, 0xb8, 0xb4, 0x7a,
  0xfc, 0x02, 0x36, 0x5b, 0x25, 0x55, 0x97, 0x31,
  0x2d, 0x5d, 0xfa, 0x98, 0xe3, 0x8a, 0x92, 0xae,
  0x05, 0xdf, 0x29, 0x10, 0x67, 0x6c, 0xba, 0xc9,
  0xd3, 0x00, 0xe6, 0xcf, 0xe1, 0x9e, 0xa8, 0x2c,
  0x63, 0x16, 0x01, 0x3f, 0x58, 0xe2, 0x89, 0xa9,
  0x0d, 0x38, 0x34, 0x1b, 0xab, 0x33, 0xff, 0xb0,
  0xbb, 0x48, 0x0c, 0x5f, 0xb9, 0xb1, 0xcd, 0x2e,
  0xc5, 0xf3, 0xdb, 0x47, 0xe5, 0xa5, 0x9c, 0x77,
  0x0a, 0xa6, 0x20, 0x68, 0xfe, 0x7f, 0xc1, 0xad
};

#define rotl16(x,n) (((x) << ((uint16_t)(n))) | ((x) >> (16 - (uint16_t)(n))))
#define rotr16(x,n) (((x) >> ((uint16_t)(n))) | ((x) << (16 - (uint16_t)(n))))

void
arctwo_encrypt (struct arctwo_ctx *ctx,
		unsigned length, uint8_t *dst, const uint8_t *src)
{
  FOR_BLOCKS (length, dst, src, ARCTWO_BLOCK_SIZE)
  {
    register unsigned i;
    uint16_t w0, w1, w2, w3;

    w0 = LE_READ_UINT16 (&src[0]);
    w1 = LE_READ_UINT16 (&src[2]);
    w2 = LE_READ_UINT16 (&src[4]);
    w3 = LE_READ_UINT16 (&src[6]);

    for (i = 0; i < 16; i++)
      {
	register unsigned j = i * 4;
	/* For some reason I cannot combine those steps. */
	w0 += (w1 & ~w3) + (w2 & w3) + ctx->S[j];
	w0 = rotl16 (w0, 1);

	w1 += (w2 & ~w0) + (w3 & w0) + ctx->S[j + 1];
	w1 = rotl16 (w1, 2);

	w2 += (w3 & ~w1) + (w0 & w1) + ctx->S[j + 2];
	w2 = rotl16 (w2, 3);

	w3 += (w0 & ~w2) + (w1 & w2) + ctx->S[j + 3];
	w3 = rotl16 (w3, 5);

	if (i == 4 || i == 10)
	  {
	    w0 += ctx->S[w3 & 63];
	    w1 += ctx->S[w0 & 63];
	    w2 += ctx->S[w1 & 63];
	    w3 += ctx->S[w2 & 63];
	  }
      }
    LE_WRITE_UINT16 (&dst[0], w0);
    LE_WRITE_UINT16 (&dst[2], w1);
    LE_WRITE_UINT16 (&dst[4], w2);
    LE_WRITE_UINT16 (&dst[6], w3);
  }
}

void
arctwo_decrypt (struct arctwo_ctx *ctx,
		unsigned length, uint8_t *dst, const uint8_t *src)
{
  FOR_BLOCKS (length, dst, src, ARCTWO_BLOCK_SIZE)
  {
    register unsigned i;
    uint16_t w0, w1, w2, w3;

    w0 = LE_READ_UINT16 (&src[0]);
    w1 = LE_READ_UINT16 (&src[2]);
    w2 = LE_READ_UINT16 (&src[4]);
    w3 = LE_READ_UINT16 (&src[6]);

    for (i = 16; i-- > 0; )
      {
	register unsigned j = i * 4;

	w3 = rotr16 (w3, 5);
	w3 -= (w0 & ~w2) + (w1 & w2) + ctx->S[j + 3];

	w2 = rotr16 (w2, 3);
	w2 -= (w3 & ~w1) + (w0 & w1) + ctx->S[j + 2];

	w1 = rotr16 (w1, 2);
	w1 -= (w2 & ~w0) + (w3 & w0) + ctx->S[j + 1];

	w0 = rotr16 (w0, 1);
	w0 -= (w1 & ~w3) + (w2 & w3) + ctx->S[j];

	if (i == 5 || i == 11)
	  {
	    w3 = w3 - ctx->S[w2 & 63];
	    w2 = w2 - ctx->S[w1 & 63];
	    w1 = w1 - ctx->S[w0 & 63];
	    w0 = w0 - ctx->S[w3 & 63];
	  }

      }
    LE_WRITE_UINT16 (&dst[0], w0);
    LE_WRITE_UINT16 (&dst[2], w1);
    LE_WRITE_UINT16 (&dst[4], w2);
    LE_WRITE_UINT16 (&dst[6], w3);
  }
}

void
arctwo_set_key_ekb (struct arctwo_ctx *ctx,
		    unsigned length, const uint8_t *key, unsigned ekb)
{
  unsigned i;
  /* Expanded key, treated as octets */
  uint8_t S[128];
  uint8_t x;

  assert (length >= ARCTWO_MIN_KEY_SIZE);
  assert (length <= ARCTWO_MAX_KEY_SIZE);
  assert (ekb <= 1024);

  for (i = 0; i < length; i++)
    S[i] = key[i];

  /* Phase 1: Expand input key to 128 bytes */
  for (i = length; i < ARCTWO_MAX_KEY_SIZE; i++)
    S[i] = arctwo_sbox[(S[i - length] + S[i - 1]) & 255];

  S[0] = arctwo_sbox[S[0]];

  /* Reduce effective key size to ekb bits, if requested by caller. */
  if (ekb > 0 && ekb < 1024)
    {
      int len = (ekb + 7) >> 3;
      i = 128 - len;
      x = arctwo_sbox[S[i] & (255 >> (7 & -ekb))];
      S[i] = x;

      while (i--)
	{
	  x = arctwo_sbox[x ^ S[i + len]];
	  S[i] = x;
	}
    }

  /* Make the expanded key endian independent. */
  for (i = 0; i < 64; i++)
    ctx->S[i] = LE_READ_UINT16(S + i * 2);
}

void
arctwo_set_key (struct arctwo_ctx *ctx, unsigned length, const uint8_t *key)
{
  arctwo_set_key_ekb (ctx, length, key, 8 * length);
}

void
arctwo_set_key_gutmann (struct arctwo_ctx *ctx,
			unsigned length, const uint8_t *key)
{
  arctwo_set_key_ekb (ctx, length, key, 0);
}