/* $OpenBSD: ctr128.c,v 1.7 2017/08/13 17:46:24 bcook Exp $ */

/* ====================================================================

 * 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

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 *    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/)"

 *

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 *    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

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 *

 * 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

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#include <openssl/crypto.h>

#include "modes_lcl.h"

#include <string.h>

#ifndef MODES_DEBUG

# ifndef NDEBUG

#  define NDEBUG

# endif

#endif

#include <assert.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(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)

{

#if BYTE_ORDER == LITTLE_ENDIAN

  ctr128_inc(counter);

#else

  size_t *data, c, n;

  data = (size_t *)counter;

  n = 16 / sizeof(size_t);

  do {

    --n;

    c = data[n];

    ++c;

    data[n] = c;

    if (c)

      return;

  } while (n);

#endif

}

#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(*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;

    }

#ifdef __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;

}

/* increment upper 96 bits of 128-bit counter by 1 */

static void ctr96_inc(unsigned char *counter) {

  u32 n=12;

  u8  c;

  do {

    --n;

    c = counter[n];

    ++c;

    counter[n] = c;

    if (c) return;

  } while (n);

}

void CRYPTO_ctr128_encrypt_ctr32(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, ctr128_f func)

{

  unsigned int n,ctr32;

  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 += (u32)blocks;

    if (ctr32 < blocks) {

      blocks -= ctr32;

      ctr32   = 0;

    }

    (*func)(in,out,blocks,key,ivec);

    /* (*ctr) 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;

}