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aes_ctr.c

/* crypto/aes/aes_ctr.c -*- mode:C; c-file-style: "eay" -*- */
/* ====================================================================
 * Copyright (c) 1998-2002 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. 
 *
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 *    distribution.
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 * 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/)"
 *
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 *    openssl-core@openssl.org.
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 * 6. Redistributions of any form whatsoever must retain the following
 *    acknowledgment:
 *    "This product includes software developed by the OpenSSL Project
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 * 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
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 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
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#ifndef AES_DEBUG
# ifndef NDEBUG
#  define NDEBUG
# endif
#endif
#include <assert.h>

#include <openssl/aes.h>
#include "aes_locl.h"

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

/* increment counter (128-bit int) by 1 */
static void AES_ctr128_inc(unsigned char *counter) {
      unsigned long c;

      /* Grab bottom dword of counter and increment */
      c = GETU32(counter + 12);
      c++;  c &= 0xFFFFFFFF;
      PUTU32(counter + 12, c);

      /* if no overflow, we're done */
      if (c)
            return;

      /* Grab 1st dword of counter and increment */
      c = GETU32(counter +  8);
      c++;  c &= 0xFFFFFFFF;
      PUTU32(counter +  8, c);

      /* if no overflow, we're done */
      if (c)
            return;

      /* Grab 2nd dword of counter and increment */
      c = GETU32(counter +  4);
      c++;  c &= 0xFFFFFFFF;
      PUTU32(counter +  4, c);

      /* if no overflow, we're done */
      if (c)
            return;

      /* Grab top dword of counter and increment */
      c = GETU32(counter +  0);
      c++;  c &= 0xFFFFFFFF;
      PUTU32(counter +  0, c);
}

/* 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 AES_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 AES_ctr128_encrypt(const unsigned char *in, unsigned char *out,
      const unsigned long length, const AES_KEY *key,
      unsigned char ivec[AES_BLOCK_SIZE],
      unsigned char ecount_buf[AES_BLOCK_SIZE],
      unsigned int *num) {

      unsigned int n;
      unsigned long l=length;

      assert(in && out && key && counter && num);
      assert(*num < AES_BLOCK_SIZE);

      n = *num;

      while (l--) {
            if (n == 0) {
                  AES_encrypt(ivec, ecount_buf, key);
                  AES_ctr128_inc(ivec);
            }
            *(out++) = *(in++) ^ ecount_buf[n];
            n = (n+1) % AES_BLOCK_SIZE;
      }

      *num=n;
}

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