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ctr128.c

/* ====================================================================
 * Copyright (c) 2008 The OpenSSL Project.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer. 
 *
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 *
 * 3. All advertising materials mentioning features or use of this
 *    software must display the following acknowledgment:
 *    "This product includes software developed by the OpenSSL Project
 *    for use in the OpenSSL Toolkit. (http://www.openssl.org/)"
 *
 * 4. The names "OpenSSL Toolkit" and "OpenSSL Project" must not be used to
 *    endorse or promote products derived from this software without
 *    prior written permission. For written permission, please contact
 *    openssl-core@openssl.org.
 *
 * 5. Products derived from this software may not be called "OpenSSL"
 *    nor may "OpenSSL" appear in their names without prior written
 *    permission of the OpenSSL Project.
 *
 * 6. Redistributions of any form whatsoever must retain the following
 *    acknowledgment:
 *    "This product includes software developed by the OpenSSL Project
 *    for use in the OpenSSL Toolkit (http://www.openssl.org/)"
 *
 * THIS SOFTWARE IS PROVIDED BY THE OpenSSL PROJECT ``AS IS'' AND ANY
 * EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE OpenSSL PROJECT OR
 * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
 * OF THE POSSIBILITY OF SUCH DAMAGE.
 * ====================================================================
 *
 */

#include "modes.h"
#include <string.h>

#ifndef MODES_DEBUG
# ifndef NDEBUG
#  define NDEBUG
# endif
#endif
#include <assert.h>

typedef unsigned int u32;
typedef unsigned char u8;

#define STRICT_ALIGNMENT
#if defined(__i386)     || defined(__i386__)    || \
    defined(__x86_64)   || defined(__x86_64__)  || \
    defined(_M_IX86)    || defined(_M_AMD64)    || defined(_M_X64) || \
    defined(__s390__)   || defined(__s390x__)
#  undef STRICT_ALIGNMENT
#endif

/* NOTE: the IV/counter CTR mode is big-endian.  The code itself
 * is endian-neutral. */

/* increment counter (128-bit int) by 1 */
static void ctr128_inc(unsigned char *counter) {
      u32 n=16;
      u8  c;

      do {
            --n;
            c = counter[n];
            ++c;
            counter[n] = c;
            if (c) return;
      } while (n);
}

#if !defined(OPENSSL_SMALL_FOOTPRINT)
static void ctr128_inc_aligned(unsigned char *counter) {
      size_t *data,c,n;
      const union { long one; char little; } is_endian = {1};

      if (is_endian.little) {
            ctr128_inc(counter);
            return;
      }

      data = (size_t *)counter;
      n = 16/sizeof(size_t);
      do {
            --n;
            c = data[n];
            ++c;
            data[n] = c;
            if (c) return;
      } while (n);
}
#endif

/* The input encrypted as though 128bit counter mode is being
 * used.  The extra state information to record how much of the
 * 128bit block we have used is contained in *num, and the
 * encrypted counter is kept in ecount_buf.  Both *num and
 * ecount_buf must be initialised with zeros before the first
 * call to CRYPTO_ctr128_encrypt().
 *
 * This algorithm assumes that the counter is in the x lower bits
 * of the IV (ivec), and that the application has full control over
 * overflow and the rest of the IV.  This implementation takes NO
 * responsability for checking that the counter doesn't overflow
 * into the rest of the IV when incremented.
 */
void CRYPTO_ctr128_encrypt(const unsigned char *in, unsigned char *out,
                  size_t len, const void *key,
                  unsigned char ivec[16], unsigned char ecount_buf[16],
                  unsigned int *num, block128_f block)
{
      unsigned int n;
      size_t l=0;

      assert(in && out && key && ecount_buf && num);
      assert(*num < 16);

      n = *num;

#if !defined(OPENSSL_SMALL_FOOTPRINT)
      if (16%sizeof(size_t) == 0) do { /* always true actually */
            while (n && len) {
                  *(out++) = *(in++) ^ ecount_buf[n];
                  --len;
                  n = (n+1) % 16;
            }

#if defined(STRICT_ALIGNMENT)
            if (((size_t)in|(size_t)out|(size_t)ivec)%sizeof(size_t) != 0)
                  break;
#endif
            while (len>=16) {
                  (*block)(ivec, ecount_buf, key);
                  ctr128_inc_aligned(ivec);
                  for (; n<16; n+=sizeof(size_t))
                        *(size_t *)(out+n) =
                        *(size_t *)(in+n) ^ *(size_t *)(ecount_buf+n);
                  len -= 16;
                  out += 16;
                  in  += 16;
                  n = 0;
            }
            if (len) {
                  (*block)(ivec, ecount_buf, key);
                  ctr128_inc_aligned(ivec);
                  while (len--) {
                        out[n] = in[n] ^ ecount_buf[n];
                        ++n;
                  }
            }
            *num = n;
            return;
      } while(0);
      /* the rest would be commonly eliminated by x86* compiler */
#endif
      while (l<len) {
            if (n==0) {
                  (*block)(ivec, ecount_buf, key);
                  ctr128_inc(ivec);
            }
            out[l] = in[l] ^ ecount_buf[n];
            ++l;
            n = (n+1) % 16;
      }

      *num=n;
}

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