path: root/cipher/cipher-aeswrap.c

/* cipher-aeswrap.c  - Generic AESWRAP mode implementation
 * Copyright (C) 2009, 2011 Free Software Foundation, Inc.
 *
 * This file is part of Libgcrypt.
 *
 * Libgcrypt 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.
 *
 * Libgcrypt 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 this program; if not, see <http://www.gnu.org/licenses/>.
 */

#include <config.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>

#include "g10lib.h"
#include "cipher.h"
#include "bufhelp.h"
#include "./cipher-internal.h"

/* Perform the wrap algorithm W as specified by NIST SP 800-38F.
   Cipher block size must be 128-bit.  */
static gcry_err_code_t
wrap (gcry_cipher_hd_t c, byte *outbuf, size_t inbuflen)
{
  int j, x;
  size_t n, i;
  unsigned char *r, *a, *b;
  unsigned char t[8];
  unsigned int burn, nburn;

#if MAX_BLOCKSIZE < 8
#error Invalid block size
#endif
  /* We require a cipher with a 128 bit block length.  */
  if (c->spec->blocksize != 16)
    return GPG_ERR_INV_LENGTH;

  /* Input data must be multiple of 64 bits.  */
  if (inbuflen % 8)
    return GPG_ERR_INV_ARG;

  n = inbuflen / 8;

  /* We need at least three 64 bit blocks.  */
  if (n < 3)
    return GPG_ERR_INV_ARG;

  burn = 0;

  r = outbuf;
  a = outbuf;  /* We store A directly in OUTBUF.  */
  b = c->u_ctr.ctr;  /* B is also used to concatenate stuff.  */

  memset (t, 0, sizeof t); /* t := 0.  */

  for (j = 0; j <= 5; j++)
    {
      for (i = 1; i < n; i++)
        {
          /* B := CIPH_k( A | R[i] ) */
          memcpy (b, a, 8);
          memcpy (b+8, r+i*8, 8);
          nburn = c->spec->encrypt (&c->context.c, b, b);
          burn = nburn > burn ? nburn : burn;
          /* t := t + 1  */
          for (x = 7; x >= 0; x--)
            if (++t[x])
              break;
          /* A := MSB_64(B) ^ t */
          cipher_block_xor (a, b, t, 8);
          /* R[i] := LSB_64(B) */
          memcpy (r+i*8, b+8, 8);
        }
   }

  if (burn > 0)
    _gcry_burn_stack (burn + 4 * sizeof(void *));

  return 0;
}


/* Perform the Key Wrap algorithm as specified by RFC3394.  We
   implement this as a mode usable with any cipher algorithm of
   blocksize 128.  */
gcry_err_code_t
_gcry_cipher_keywrap_encrypt (gcry_cipher_hd_t c,
                              byte *outbuf, size_t outbuflen,
                              const byte *inbuf, size_t inbuflen)
{
  gcry_err_code_t err;
  unsigned char *r = outbuf;

  /* We require a cipher with a 128 bit block length.  */
  if (c->spec->blocksize != 16)
    return GPG_ERR_INV_LENGTH;

  /* The output buffer must be able to hold the input data plus one
     additional block.  */
  if (outbuflen < inbuflen + 8)
    return GPG_ERR_BUFFER_TOO_SHORT;
  /* Input data must be multiple of 64 bits.  */
  if (inbuflen % 8)
    return GPG_ERR_INV_ARG;

  /* We need at least two 64 bit blocks.  */
  if ((inbuflen / 8) < 2)
    return GPG_ERR_INV_ARG;

  /* Copy the inbuf to the outbuf. */
  memmove (r+8, inbuf, inbuflen);

  /* If an IV has been set we use that IV as the Alternative Initial
     Value; if it has not been set we use the standard value.  */
  if (c->marks.iv)
    memcpy (r, c->u_iv.iv, 8);
  else
    memset (r, 0xa6, 8);

  err = wrap (c, r, inbuflen + 8);

  return err;
}


static const unsigned char icv2[] = { 0xA6, 0x59, 0x59, 0xA6 };

/* Perform the Key Wrap algorithm as specified by RFC5649.  */
gcry_err_code_t
_gcry_cipher_keywrap_encrypt_padding (gcry_cipher_hd_t c,
                                      byte *outbuf, size_t outbuflen,
                                      const byte *inbuf, size_t inbuflen)
{
  gcry_err_code_t err;
  unsigned char *r = outbuf;
  unsigned int padlen;

  /* We require a cipher with a 128 bit block length.  */
  if (c->spec->blocksize != 16)
    return GPG_ERR_INV_LENGTH;

  /* The output buffer must be able to hold the input data plus one
     additional block and padding.  */
  if (outbuflen < ((inbuflen + 7)/8)*8 + 8)
    return GPG_ERR_BUFFER_TOO_SHORT;

  if (inbuflen % 8)
    padlen = 8 - (inbuflen % 8);
  else
    padlen = 0;

  memcpy (r, icv2, 4);
  r[4] = ((inbuflen >> 24) & 0xff);
  r[5] = ((inbuflen >> 16) & 0xff);
  r[6] = ((inbuflen >> 8) & 0xff);
  r[7] = (inbuflen & 0xff);
  memcpy (r+8, inbuf, inbuflen);
  if (padlen)
    memset (r+8+inbuflen, 0, padlen);

  if (inbuflen <= 8)
    {
      unsigned int burn;

      burn = c->spec->encrypt (&c->context.c, r, r);
      if (burn > 0)
        _gcry_burn_stack (burn + 4 * sizeof(void *));
      err = 0;
    }
  else
    err = wrap (c, r, ((inbuflen + 7)/8)*8 + 8);

  return err;
}


/* Perform the unwrap algorithm W^-1 as specified by NIST SP 800-38F.
   Cipher block size must be 128-bit.  */
static gcry_err_code_t
unwrap (gcry_cipher_hd_t c, byte *outbuf, const byte *inbuf, size_t inbuflen)
{
  int j, x;
  size_t n, i;
  unsigned char *r, *a, *b;
  unsigned char t[8];
  unsigned int burn, nburn;

#if MAX_BLOCKSIZE < 8
#error Invalid block size
#endif
  /* We require a cipher with a 128 bit block length.  */
  if (c->spec->blocksize != 16)
    return GPG_ERR_INV_LENGTH;

  /* Input data must be multiple of 64 bits.  */
  if (inbuflen % 8)
    return GPG_ERR_INV_ARG;

  n = inbuflen / 8;

  /* We need at least three 64 bit blocks.  */
  if (n < 3)
    return GPG_ERR_INV_ARG;

  burn = 0;

  r = outbuf;
  a = c->lastiv;  /* We use c->LASTIV as buffer for A.  */
  b = c->u_ctr.ctr;     /* B is also used to concatenate stuff.  */

  /* Copy the inbuf to the outbuf and save A. */
  memcpy (a, inbuf, 8);
  memmove (r, inbuf+8, inbuflen-8);
  n--; /* Reduce to actual number of data blocks.  */

  /* t := 6 * n  */
  i = n * 6;  /* The range is valid because: n = inbuflen / 8 - 1.  */
  for (x=0; x < 8 && x < sizeof (i); x++)
    t[7-x] = i >> (8*x);
  for (; x < 8; x++)
    t[7-x] = 0;

  for (j = 5; j >= 0; j--)
    {
      for (i = n; i >= 1; i--)
        {
          /* B := CIPH_k^-1( (A ^ t)| R[i] ) */
          cipher_block_xor (b, a, t, 8);
          memcpy (b+8, r+(i-1)*8, 8);
          nburn = c->spec->decrypt (&c->context.c, b, b);
          burn = nburn > burn ? nburn : burn;
          /* t := t - 1  */
          for (x = 7; x >= 0; x--)
            if (--t[x] != 0xff)
              break;
          /* A := MSB_64(B) */
          memcpy (a, b, 8);
          /* R[i] := LSB_64(B) */
          memcpy (r+(i-1)*8, b+8, 8);
        }
   }
  wipememory (b, 16);  /* Clear scratch area.  */

  if (burn > 0)
    _gcry_burn_stack (burn + 4 * sizeof(void *));

  return 0;
}


/* Perform the Key Unwrap algorithm as specified by RFC3394 and
   RFC5649.  */
gcry_err_code_t
_gcry_cipher_keywrap_decrypt_auto (gcry_cipher_hd_t c,
                                   byte *outbuf, size_t outbuflen,
                                   const byte *inbuf, size_t inbuflen)
{
  gcry_err_code_t err;

  /* We require a cipher with a 128 bit block length.  */
  if (c->spec->blocksize != 16)
    return GPG_ERR_INV_LENGTH;

  /* The output buffer must be able to hold the input data minus one
     additional block.  Fixme: The caller has more restrictive checks
     - we may want to fix them for this mode.  */
  if (outbuflen + 8 < inbuflen)
    return GPG_ERR_BUFFER_TOO_SHORT;
  /* Input data must be multiple of 64 bits.  */
  if (inbuflen % 8)
    return GPG_ERR_INV_ARG;

  if (inbuflen == 16)
    {
      unsigned int burn;
      unsigned char t[16];

      if (!(c->flags & GCRY_CIPHER_EXTENDED))
        return GPG_ERR_BUFFER_TOO_SHORT;

      burn = c->spec->decrypt (&c->context.c, t, inbuf);
      if (burn > 0)
        _gcry_burn_stack (burn + 4 * sizeof(void *));

      if (memcmp (t, icv2, 4))
        err = GPG_ERR_CHECKSUM;
      else
        {
          unsigned int plen = (t[4]<<24) | (t[5]<<16) | (t[6]<<8) | t[7];

          err = 0;
          if (plen > 8)
            err = GPG_ERR_CHECKSUM;
          else if (plen)
            {
              int i;

              for (i = 0; i < 16 - (8+plen); i++)
                if (t[8+plen+i])
                  {
                    err = GPG_ERR_CHECKSUM;
                    break;
                  }
              if (!err)
                {
                  memcpy (outbuf, t+8, 8);
                  memcpy (c->u_mode.wrap.plen, t+4, 4);
                }
            }
        }
    }
  else
    {
      /* We need at least three 64 bit blocks.  */
      if ((inbuflen / 8) < 3)
        return GPG_ERR_INV_ARG;

      err = unwrap (c, outbuf, inbuf, inbuflen);
      if (!err)
        {
          unsigned char *a;

          a = c->lastiv;  /* We use c->LASTIV as buffer for A.  */

          /* If an IV has been set we compare against this Alternative Initial
             Value; if it has not been set we compare against the standard IV.  */
          if (c->marks.iv && !memcmp (a, c->u_iv.iv, 8))
            memset (c->u_mode.wrap.plen, 0, 4);
          else if (!memcmp (a, icv2, 4)) /* It's a packet wrapped by KWP.  */
            {
              unsigned int plen = (a[4]<<24) | (a[5]<<16) | (a[6]<<8) | a[7];
              int padlen = inbuflen - 8 - plen;

              if (!(c->flags & GCRY_CIPHER_EXTENDED))
                err = GPG_ERR_CHECKSUM;
              else if (padlen < 0 || padlen > 7)
                err = GPG_ERR_CHECKSUM;
              else if (padlen)
                {
                  int i;

                  for (i = 0; i < padlen; i++)
                    if (outbuf[plen+i])
                      {
                        err = GPG_ERR_CHECKSUM;
                        break;
                      }
                }
              if (!err)
                memcpy (c->u_mode.wrap.plen, a+4, 4);
            }
          else                  /* It's a packet wrapped by KW.  */
            {
              int i;

              for (i = 0; i < 8; i++)
                if (a[i] != 0xa6)
                  {
                    err = GPG_ERR_CHECKSUM;
                    break;
                  }
              if (!err)
                memset (c->u_mode.wrap.plen, 0, 4);
            }
        }
    }

  return err;
}