crypto/modes/ctr.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 <openssl/modes.h>

#include <assert.h>
#include <string.h>

#include "internal.h"


/* 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(uint8_t *counter) {
  uint32_t n = 16;
  uint8_t c;

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

/* 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 responsibility for checking that
 * the counter doesn't overflow into the rest of the IV when incremented. */
void CRYPTO_ctr128_encrypt(const uint8_t *in, uint8_t *out, size_t len,
                           const void *key, uint8_t ivec[16],
                           uint8_t ecount_buf[16], unsigned int *num,
                           block128_f block) {
  unsigned int n;

  assert(key && ecount_buf && num);
  assert(len == 0 || (in && out));
  assert(*num < 16);
  assert((16 % sizeof(size_t)) == 0);

  n = *num;

  while (n && len) {
    *(out++) = *(in++) ^ ecount_buf[n];
    --len;
    n = (n + 1) % 16;
  }

#if STRICT_ALIGNMENT
  if (((size_t)in | (size_t)out | (size_t)ivec) % sizeof(size_t) != 0) {
    size_t l = 0;
    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;
    return;
  }
#endif

  while (len >= 16) {
    (*block)(ivec, ecount_buf, key);
    ctr128_inc(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(ivec);
    while (len--) {
      out[n] = in[n] ^ ecount_buf[n];
      ++n;
    }
  }
  *num = n;
}

/* increment upper 96 bits of 128-bit counter by 1 */
static void ctr96_inc(uint8_t *counter) {
  uint32_t n = 12;
  uint8_t c;

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

void CRYPTO_ctr128_encrypt_ctr32(const uint8_t *in, uint8_t *out,
                                 size_t len, const void *key,
                                 uint8_t ivec[16],
                                 uint8_t ecount_buf[16],
                                 unsigned int *num, ctr128_f func) {
  unsigned int n, ctr32;

  assert(key && ecount_buf && num);
  assert(len == 0 || (in && out));
  assert(*num < 16);

  n = *num;

  while (n && len) {
    *(out++) = *(in++) ^ ecount_buf[n];
    --len;
    n = (n + 1) % 16;
  }

  ctr32 = GETU32(ivec + 12);
  while (len >= 16) {
    size_t blocks = len / 16;
    /* 1<<28 is just a not-so-small yet not-so-large number...
     * Below condition is practically never met, but it has to
     * be checked for code correctness. */
    if (sizeof(size_t) > sizeof(unsigned int) && blocks > (1U << 28)) {
      blocks = (1U << 28);
    }
    /* As (*func) operates on 32-bit counter, caller
     * has to handle overflow. 'if' below detects the
     * overflow, which is then handled by limiting the
     * amount of blocks to the exact overflow point... */
    ctr32 += (uint32_t)blocks;
    if (ctr32 < blocks) {
      blocks -= ctr32;
      ctr32 = 0;
    }
    (*func)(in, out, blocks, key, ivec);
    /* (*func) does not update ivec, caller does: */
    PUTU32(ivec + 12, ctr32);
    /* ... overflow was detected, propogate carry. */
    if (ctr32 == 0) {
      ctr96_inc(ivec);
    }
    blocks *= 16;
    len -= blocks;
    out += blocks;
    in += blocks;
  }
  if (len) {
    memset(ecount_buf, 0, 16);
    (*func)(ecount_buf, ecount_buf, 1, key, ivec);
    ++ctr32;
    PUTU32(ivec + 12, ctr32);
    if (ctr32 == 0) {
      ctr96_inc(ivec);
    }
    while (len--) {
      out[n] = in[n] ^ ecount_buf[n];
      ++n;
    }
  }

  *num = n;
}