/* cipher-aead.c - Enciphering filter for AEAD modes

 * Copyright (C) 2018 Werner koch

 *

 * This file is part of GnuPG.

 *

 * GnuPG is free software; you can redistribute it and/or modify

 * it under the terms of the GNU General Public License as published by

 * the Free Software Foundation; either version 3 of the License, or

 * (at your option) any later version.

 *

 * GnuPG 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 General Public License for more details.

 *

 * You should have received a copy of the GNU General Public License

 * along with this program; if not, see <https://www.gnu.org/licenses/>.

 * SPDX-License-Identifier: GPL-3.0+

 */

#include <config.h>

#include <stdio.h>

#include <stdlib.h>

#include <string.h>

#include <errno.h>

#include "gpg.h"

#include "../common/status.h"

#include "../common/iobuf.h"

#include "../common/util.h"

#include "filter.h"

#include "packet.h"

#include "options.h"

#include "main.h"

/* The size of the buffer we allocate to encrypt the data.  This must

 * be a multiple of the OCB blocksize (16 byte).  */

#define AEAD_ENC_BUFFER_SIZE (64*1024)

/* Wrapper around iobuf_write to make sure that a proper error code is

 * always returned.  */

static gpg_error_t

my_iobuf_write (iobuf_t a, const void *buffer, size_t buflen)

{

  if (iobuf_write (a, buffer, buflen))

    {

      gpg_error_t err = iobuf_error (a);

      if (!err || !gpg_err_code (err)) /* (The latter should never happen) */

        err = gpg_error (GPG_ERR_EIO);

      return err;

    }

  return 0;

}

/* Set the nonce and the additional data for the current chunk.  If

 * FINAL is set the final AEAD chunk is processed.  This also reset

 * the encryption machinery so that the handle can be used for a new

 * chunk.  */

static gpg_error_t

set_nonce_and_ad (cipher_filter_context_t *cfx, int final)

{

  gpg_error_t err;

  unsigned char nonce[16];

  unsigned char ad[21];

  int i;

  switch (cfx->dek->use_aead)

    {

    case AEAD_ALGO_OCB:

      memcpy (nonce, cfx->startiv, 15);

      i = 7;

      break;

    case AEAD_ALGO_EAX:

      memcpy (nonce, cfx->startiv, 16);

      i = 8;

      break;

    default:

      BUG ();

    }

  nonce[i++] ^= cfx->chunkindex >> 56;

  nonce[i++] ^= cfx->chunkindex >> 48;

  nonce[i++] ^= cfx->chunkindex >> 40;

  nonce[i++] ^= cfx->chunkindex >> 32;

  nonce[i++] ^= cfx->chunkindex >> 24;

  nonce[i++] ^= cfx->chunkindex >> 16;

  nonce[i++] ^= cfx->chunkindex >>  8;

  nonce[i++] ^= cfx->chunkindex;

  if (DBG_CRYPTO)

    log_printhex (nonce, 15, "nonce:");

  err = gcry_cipher_setiv (cfx->cipher_hd, nonce, i);

  if (err)

    return err;

  ad[0] = (0xc0 | PKT_ENCRYPTED_AEAD);

  ad[1] = 1;

  ad[2] = cfx->dek->algo;

  ad[3] = cfx->dek->use_aead;

  ad[4] = cfx->chunkbyte;

  ad[5] = cfx->chunkindex >> 56;

  ad[6] = cfx->chunkindex >> 48;

  ad[7] = cfx->chunkindex >> 40;

  ad[8] = cfx->chunkindex >> 32;

  ad[9] = cfx->chunkindex >> 24;

  ad[10]= cfx->chunkindex >> 16;

  ad[11]= cfx->chunkindex >>  8;

  ad[12]= cfx->chunkindex;

  if (final)

    {

      ad[13] = cfx->total >> 56;

      ad[14] = cfx->total >> 48;

      ad[15] = cfx->total >> 40;

      ad[16] = cfx->total >> 32;

      ad[17] = cfx->total >> 24;

      ad[18] = cfx->total >> 16;

      ad[19] = cfx->total >>  8;

      ad[20] = cfx->total;

    }

  if (DBG_CRYPTO)

    log_printhex (ad, final? 21 : 13, "authdata:");

  return gcry_cipher_authenticate (cfx->cipher_hd, ad, final? 21 : 13);

}

static gpg_error_t

write_header (cipher_filter_context_t *cfx, iobuf_t a)

{

  gpg_error_t err;

  PACKET pkt;

  PKT_encrypted ed;

  unsigned int blocksize;

  unsigned int startivlen;

  enum gcry_cipher_modes ciphermode;

  log_assert (cfx->dek->use_aead);

  blocksize = openpgp_cipher_get_algo_blklen (cfx->dek->algo);

  if (blocksize != 16 )

    log_fatal ("unsupported blocksize %u for AEAD\n", blocksize);

  err = openpgp_aead_algo_info (cfx->dek->use_aead, &ciphermode, &startivlen);

  if (err)

    goto leave;

  log_assert (opt.chunk_size >= 6 && opt.chunk_size <= 62);

  cfx->chunkbyte = opt.chunk_size - 6;

  cfx->chunksize = (uint64_t)1 << (cfx->chunkbyte + 6);

  cfx->chunklen = 0;

  cfx->bufsize = AEAD_ENC_BUFFER_SIZE;

  cfx->buflen = 0;

  cfx->buffer = xtrymalloc (cfx->bufsize);

  if (!cfx->buffer)

    return gpg_error_from_syserror ();

  memset (&ed, 0, sizeof ed);

  ed.new_ctb = 1;  /* (Is anyway required for the packet type).  */

  ed.len = 0; /* fixme: cfx->datalen */

  ed.extralen    = startivlen + 16; /* (16 is the taglen) */

  ed.cipher_algo = cfx->dek->algo;

  ed.aead_algo   = cfx->dek->use_aead;

  ed.chunkbyte   = cfx->chunkbyte;

  init_packet (&pkt);

  pkt.pkttype = PKT_ENCRYPTED_AEAD;

  pkt.pkt.encrypted = &ed;

  if (DBG_FILTER)

    log_debug ("aead packet: len=%lu extralen=%d\n",

               (unsigned long)ed.len, ed.extralen);

  write_status_printf (STATUS_BEGIN_ENCRYPTION, "0 %d %d",

                       cfx->dek->algo, ed.aead_algo);

  print_cipher_algo_note (cfx->dek->algo);

  if (build_packet( a, &pkt))

    log_bug ("build_packet(ENCRYPTED_AEAD) failed\n");

  log_assert (sizeof cfx->startiv >= startivlen);

  gcry_randomize (cfx->startiv, startivlen, GCRY_STRONG_RANDOM);

  err = my_iobuf_write (a, cfx->startiv, startivlen);

  if (err)

    goto leave;

  err = openpgp_cipher_open (&cfx->cipher_hd,

                             cfx->dek->algo,

                             ciphermode,

                             GCRY_CIPHER_SECURE);

  if (err)

    goto leave;

  if (DBG_CRYPTO)

    log_printhex (cfx->dek->key, cfx->dek->keylen, "thekey:");

  err = gcry_cipher_setkey (cfx->cipher_hd, cfx->dek->key, cfx->dek->keylen);

  if (err)

    return err;

  cfx->wrote_header = 1;

 leave:

  return err;

}

/* Get and write the auth tag to stream A.  */

static gpg_error_t

write_auth_tag (cipher_filter_context_t *cfx, iobuf_t a)

{

  gpg_error_t err;

  char tag[16];

  err = gcry_cipher_gettag (cfx->cipher_hd, tag, 16);

  if (err)

    goto leave;

  err = my_iobuf_write (a, tag, 16);

  if (err)

    goto leave;

 leave:

  if (err)

    log_error ("write_auth_tag failed: %s\n", gpg_strerror (err));

  return err;

}

/* Write the final chunk to stream A.  */

static gpg_error_t

write_final_chunk (cipher_filter_context_t *cfx, iobuf_t a)

{

  gpg_error_t err;

  char dummy[1];

  err = set_nonce_and_ad (cfx, 1);

  if (err)

    goto leave;

  gcry_cipher_final (cfx->cipher_hd);

  /* Encrypt an empty string.  */

  err = gcry_cipher_encrypt (cfx->cipher_hd, dummy, 0, NULL, 0);

  if (err)

    goto leave;

  err = write_auth_tag (cfx, a);

 leave:

  return err;

}

/* The core of the flush sub-function of cipher_filter_aead.   */

static gpg_error_t

do_flush (cipher_filter_context_t *cfx, iobuf_t a, byte *buf, size_t size)

{

  gpg_error_t err = 0;

  int finalize = 0;

  size_t n;

  /* Put the data into a buffer, flush and encrypt as needed.  */

  if (DBG_FILTER)

    log_debug ("flushing %zu bytes (cur buflen=%zu)\n", size, cfx->buflen);

  do

    {

      const unsigned fast_threshold = 512;

      const byte *src_buf = NULL;

      int enc_now = 0;

      if (cfx->buflen + size < cfx->bufsize)

        n = size;

      else

        n = cfx->bufsize - cfx->buflen;

      if (cfx->buflen % fast_threshold != 0)

  {

    /* Attempt to align cfx->buflen to fast threshold size first. */

    size_t nalign = fast_threshold - (cfx->buflen % fast_threshold);

    if (nalign < n)

      {

        n = nalign;

      }

  }

      else if (cfx->buflen == 0 && n >= fast_threshold)

  {

    /* Handle large input buffers as multiple of cipher blocksize. */

    n = (n / 16) * 16;

  }

      if (cfx->chunklen + cfx->buflen + n >= cfx->chunksize)

        {

          size_t n1 = cfx->chunksize - (cfx->chunklen + cfx->buflen);

          finalize = 1;

          if (DBG_FILTER)

            log_debug ("chunksize %"PRIu64" reached;"

                       " cur buflen=%zu using %zu of %zu\n",

                       cfx->chunksize, cfx->buflen,

                       n1, n);

          n = n1;

        }

      if (!finalize && cfx->buflen % 16 == 0 && cfx->buflen > 0

    && size >= fast_threshold)

  {

    /* If cfx->buffer is aligned and remaining input buffer length

     * is long, encrypt cfx->buffer inplace now to allow fast path

     * handling on next loop iteration. */

    src_buf = cfx->buffer;

    enc_now = 1;

    n = 0;

  }

      else if (cfx->buflen == 0 && n >= fast_threshold)

  {

    /* Fast path for large input buffer. This avoids memcpy and

     * instead encrypts directly from input to cfx->buffer. */

    log_assert (n % 16 == 0 || finalize);

    src_buf = buf;

    cfx->buflen = n;

    buf += n;

    size -= n;

    enc_now = 1;

  }

      else if (n > 0)

  {

    memcpy (cfx->buffer + cfx->buflen, buf, n);

    src_buf = cfx->buffer;

    cfx->buflen += n;

    buf  += n;

    size -= n;

  }

      if (cfx->buflen == cfx->bufsize || enc_now || finalize)

        {

          if (DBG_FILTER)

            log_debug ("encrypting: size=%zu buflen=%zu %s%s n=%zu\n",

                       size, cfx->buflen, finalize?"(finalize)":"",

           enc_now?"(now)":"", n);

          if (!cfx->chunklen)

            {

              if (DBG_FILTER)

                log_debug ("start encrypting a new chunk\n");

              err = set_nonce_and_ad (cfx, 0);

              if (err)

                goto leave;

            }

          if (finalize)

            gcry_cipher_final (cfx->cipher_hd);

          if (DBG_FILTER)

            {

              if (finalize)

                log_printhex (src_buf, cfx->buflen, "plain(1):");

              else if (cfx->buflen > 32)

                log_printhex (src_buf + cfx->buflen - 32, 32,

                              "plain(last32):");

            }

          /* Take care: even with a buflen of zero an encrypt needs to

           * be called after gcry_cipher_final and before

           * gcry_cipher_gettag - at least with libgcrypt 1.8 and OCB

           * mode.  */

    err = gcry_cipher_encrypt (cfx->cipher_hd, cfx->buffer,

             cfx->buflen, src_buf, cfx->buflen);

          if (err)

            goto leave;

          if (finalize && DBG_FILTER)

            log_printhex (cfx->buffer, cfx->buflen, "ciphr(1):");

          err = my_iobuf_write (a, cfx->buffer, cfx->buflen);

          if (err)

            goto leave;

          cfx->chunklen += cfx->buflen;

          cfx->total += cfx->buflen;

          cfx->buflen = 0;

          if (finalize)

            {

              if (DBG_FILTER)

                log_debug ("writing tag: chunklen=%ju total=%ju\n",

                           (uintmax_t)cfx->chunklen, (uintmax_t)cfx->total);

              err = write_auth_tag (cfx, a);

              if (err)

                goto leave;

              cfx->chunkindex++;

              cfx->chunklen = 0;

              finalize = 0;

            }

        }

    }

  while (size);

 leave:

  return err;

}

/* The core of the free sub-function of cipher_filter_aead.   */

static gpg_error_t

do_free (cipher_filter_context_t *cfx, iobuf_t a)

{

  gpg_error_t err = 0;

  if (DBG_FILTER)

    log_debug ("do_free: buflen=%zu\n", cfx->buflen);

  if (cfx->chunklen || cfx->buflen)

    {

      if (DBG_FILTER)

        log_debug ("encrypting last %zu bytes of the last chunk\n",cfx->buflen);

      if (!cfx->chunklen)

        {

          if (DBG_FILTER)

            log_debug ("start encrypting a new chunk\n");

          err = set_nonce_and_ad (cfx, 0);

          if (err)

            goto leave;

        }

      gcry_cipher_final (cfx->cipher_hd);

      err = gcry_cipher_encrypt (cfx->cipher_hd, cfx->buffer, cfx->buflen,

                                 NULL, 0);

      if (err)

        goto leave;

      err = my_iobuf_write (a, cfx->buffer, cfx->buflen);

      if (err)

        goto leave;

      /* log_printhex (cfx->buffer, cfx->buflen, "wrote:"); */

      cfx->chunklen += cfx->buflen;

      cfx->total += cfx->buflen;

      /* Get and write the authentication tag.  */

      if (DBG_FILTER)

        log_debug ("writing tag: chunklen=%ju total=%ju\n",

                   (uintmax_t)cfx->chunklen, (uintmax_t)cfx->total);

      err = write_auth_tag (cfx, a);

      if (err)

        goto leave;

      cfx->chunkindex++;

      cfx->chunklen = 0;

    }

  /* Write the final chunk.  */

  if (DBG_FILTER)

    log_debug ("creating final chunk\n");

  err = write_final_chunk (cfx, a);

 leave:

  xfree (cfx->buffer);

  cfx->buffer = NULL;

  gcry_cipher_close (cfx->cipher_hd);

  cfx->cipher_hd = NULL;

  return err;

}

/*

 * This filter is used to encrypt data with an AEAD algorithm

 */

int

cipher_filter_aead (void *opaque, int control,

                    iobuf_t a, byte *buf, size_t *ret_len)

{

  cipher_filter_context_t *cfx = opaque;

  size_t size = *ret_len;

  int rc = 0;

  if (control == IOBUFCTRL_UNDERFLOW) /* decrypt */

    {

      rc = -1; /* not used */

    }

  else if (control == IOBUFCTRL_FLUSH) /* encrypt */

    {

      if (!cfx->wrote_header && (rc=write_header (cfx, a)))

        ;

      else

        rc = do_flush (cfx, a, buf, size);

    }

  else if (control == IOBUFCTRL_FREE)

    {

      rc = do_free (cfx, a);

    }

  else if (control == IOBUFCTRL_DESC)

    {

      mem2str (buf, "cipher_filter_aead", *ret_len);

    }

  return rc;

}