libtomcrypt/demos/gcm-file/gcm_filehandle.c

/* LibTomCrypt, modular cryptographic library -- Tom St Denis */
/* SPDX-License-Identifier: Unlicense */

#include "tomcrypt.h"

/**
  @file gcm_filehandle.c
  GCM process a filehandle, Steffen Jaeckel
*/

#ifdef LTC_GCM_MODE
#ifndef LTC_NO_FILE

#if defined(_MSC_VER)
#define ftruncate _chsize
#else
#include <unistd.h>
#endif

/**
  Process a filehandle.

  This uses the widely established scheme where the tag is appended
  to the ciphertext.

  encrypted_file = aesgcm(plain_file) | aesgcm_tag(plain_file)

  Depending on 'direction' this function does:

    Encrypt file 'in' to 'out' and append the tag of length 'taglen'
    to 'out'.

      or

    Decrypt file 'in' to 'out' and check the tag of length 'taglen'
    and strip the tag from 'in'.

  In error-cases 'out' will be zeroed out first and then truncated to
  a length of 0.

  @param cipher            Index of cipher to use
  @param key               The secret key
  @param keylen            The length of the secret key
  @param IV                The initial vector
  @param IVlen             The length of the initial vector
  @param adata             The additional authentication data (header)
  @param adatalen          The length of the adata
  @param in                The input file
  @param out               The output file
  @param taglen            The MAC tag length
  @param direction         Encrypt or Decrypt mode (GCM_ENCRYPT or GCM_DECRYPT)
  @param res               [out] Result of the operation, 1==valid, 0==invalid
  @return CRYPT_OK on success
 */
int gcm_filehandle(      int           cipher,
                   const unsigned char *key,    unsigned long keylen,
                   const unsigned char *IV,     unsigned long IVlen,
                   const unsigned char *adata,  unsigned long adatalen,
                                  FILE *in,
                                  FILE *out,
                         unsigned long taglen,
                                   int direction,
                                   int *res)
{
    void      *orig;
    gcm_state *gcm;
    int        err;
    unsigned char *buf, tag[16];
    size_t x, tot_data;
    unsigned long tag_len;

    LTC_ARGCHK(in  != NULL);
    LTC_ARGCHK(out != NULL);
    LTC_ARGCHK(res != NULL);

    *res = 0;

    if ((err = cipher_is_valid(cipher)) != CRYPT_OK) {
       return err;
    }

#ifndef LTC_GCM_TABLES_SSE2
    orig = gcm = XMALLOC(sizeof(*gcm));
#else
    orig = gcm = XMALLOC(sizeof(*gcm) + 16);
#endif
    if (gcm == NULL) {
        return CRYPT_MEM;
    }

    if ((buf = XMALLOC(LTC_FILE_READ_BUFSIZE)) == NULL) {
        XFREE(gcm);
        return CRYPT_MEM;
    }

   /* Force GCM to be on a multiple of 16 so we can use 128-bit aligned operations
    * note that we only modify gcm and keep orig intact.  This code is not portable
    * but again it's only for SSE2 anyways, so who cares?
    */
#ifdef LTC_GCM_TABLES_SSE2
   if ((unsigned long)gcm & 15) {
      gcm = (gcm_state *)((unsigned long)gcm + (16 - ((unsigned long)gcm & 15)));
   }
#endif

    if ((err = gcm_init(gcm, cipher, key, keylen)) != CRYPT_OK) {
       goto LBL_ERR;
    }
    if ((err = gcm_add_iv(gcm, IV, IVlen)) != CRYPT_OK) {
       goto LBL_ERR;
    }
    if ((err = gcm_add_aad(gcm, adata, adatalen)) != CRYPT_OK) {
       goto LBL_ERR;
    }

    fseek(in, 0, SEEK_END);
    tot_data = ftell(in);
    if (direction == GCM_DECRYPT) {
       tot_data -= taglen;
    }
    rewind(in);
    do {
       x = MIN(tot_data, LTC_FILE_READ_BUFSIZE);
       x = fread(buf, 1, x, in);
       tot_data -= x;
       if ((err = gcm_process(gcm, buf, (unsigned long)x, buf, direction)) != CRYPT_OK) {
          goto LBL_CLEANBUF;
       }
       if(fwrite(buf, 1, x, out) != x) {
          err = CRYPT_ERROR;
          goto LBL_CLEANBUF;
       }
    } while (x == LTC_FILE_READ_BUFSIZE);

    tag_len = taglen;
    if ((err = gcm_done(gcm, tag, &tag_len)) != CRYPT_OK) {
       goto LBL_CLEANBUF;
    }
    if (tag_len != taglen) {
       err = CRYPT_ERROR;
       goto LBL_CLEANBUF;
    }

    if (direction == GCM_DECRYPT) {
       x = fread(buf, 1, taglen, in);
       if (x != taglen) {
          err = CRYPT_ERROR;
          goto LBL_CLEANBUF;
       }

       if (XMEM_NEQ(buf, tag, taglen) == 0) {
          *res = 1;
       }
    } else {
       if(fwrite(tag, 1, taglen, out) != taglen) {
          err = CRYPT_ERROR;
          goto LBL_CLEANBUF;
       }
       *res = 1;
    }

LBL_CLEANBUF:
    zeromem(buf, LTC_FILE_READ_BUFSIZE);
    zeromem(tag, sizeof(tag));
LBL_ERR:
#ifdef LTC_CLEAN_STACK
#ifndef LTC_GCM_TABLES_SSE2
    zeromem(orig, sizeof(*gcm));
#else
    zeromem(orig, sizeof(*gcm) + 16);
#endif
#endif
    if(*res == 0) {
       x = ftell(out);
       rewind(out);
       while((size_t)ftell(out) < x) {
          fwrite(buf, 1, LTC_FILE_READ_BUFSIZE, out);
       }
       if(ftruncate(fileno(out), 0)) {
          /* well, what shall we do here... */
       }
    }
    fflush(out);

    XFREE(buf);
    XFREE(orig);

    return err;
}
#endif
#endif