programs/aes/aescrypt2.c - mirror/mbed-tls.git - TrustedFirmware Git Browser

 /*
  *  AES-256 file encryption program
  *
  *  Copyright (C) 2006-2015, ARM Limited, All Rights Reserved
  *  SPDX-License-Identifier: Apache-2.0
  *
  *  Licensed under the Apache License, Version 2.0 (the "License"); you may
  *  not use this file except in compliance with the License.
  *  You may obtain a copy of the License at
  *
  *  http://www.apache.org/licenses/LICENSE-2.0
  *
  *  Unless required by applicable law or agreed to in writing, software
  *  distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
  *  WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  *  See the License for the specific language governing permissions and
  *  limitations under the License.
  *
  *  This file is part of mbed TLS (https://tls.mbed.org)
  */

 /* Enable definition of fileno() even when compiling with -std=c99. Must be
  * set before config.h, which pulls in glibc's features.h indirectly.
  * Harmless on other platforms. */
 #define _POSIX_C_SOURCE 1

 #if !defined(MBEDTLS_CONFIG_FILE)
 #include "mbedtls/config.h"
 #else
 #include MBEDTLS_CONFIG_FILE
 #endif

 #if defined(MBEDTLS_PLATFORM_C)
 #include "mbedtls/platform.h"
 #else
 #include <stdio.h>
 #include <stdlib.h>
 #define mbedtls_fprintf         fprintf
 #define mbedtls_printf          printf
 #define mbedtls_exit            exit
 #define MBEDTLS_EXIT_SUCCESS    EXIT_SUCCESS
 #define MBEDTLS_EXIT_FAILURE    EXIT_FAILURE
 #endif /* MBEDTLS_PLATFORM_C */

 #include "mbedtls/aes.h"
 #include "mbedtls/md.h"
 #include "mbedtls/platform_util.h"

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

 #if defined(_WIN32)
 #include <windows.h>
 #if !defined(_WIN32_WCE)
 #include <io.h>
 #endif
 #else
 #include <sys/types.h>
 #include <unistd.h>
 #endif

 #define MODE_ENCRYPT    0
 #define MODE_DECRYPT    1

 #define USAGE   \
     "\n  aescrypt2 <mode> <input filename> <output filename> <key>\n" \
     "\n   <mode>: 0 = encrypt, 1 = decrypt\n" \
     "\n  example: aescrypt2 0 file file.aes hex:E76B2413958B00E193\n" \
     "\n"

 #if !defined(MBEDTLS_AES_C) || !defined(MBEDTLS_SHA256_C) || \
     !defined(MBEDTLS_FS_IO) || !defined(MBEDTLS_MD_C)
 int main( void )
 {
     mbedtls_printf("MBEDTLS_AES_C and/or MBEDTLS_SHA256_C "
                     "and/or MBEDTLS_FS_IO and/or MBEDTLS_MD_C "
                     "not defined.\n");
     return( 0 );
 }
 #else


 int main( int argc, char *argv[] )
 {
     int ret = 0;
     int exit_code = MBEDTLS_EXIT_FAILURE;

     unsigned int i, n;
     int mode, lastn;
     size_t keylen;
     FILE *fkey, *fin = NULL, *fout = NULL;

     char *p;

     unsigned char IV[16];
     unsigned char tmp[16];
     unsigned char key[512];
     unsigned char digest[64];
     unsigned char buffer[1024];
     unsigned char diff;

     mbedtls_aes_context aes_ctx;
     mbedtls_md_context_t sha_ctx;

 #if defined(_WIN32_WCE)
     long filesize, offset;
 #elif defined(_WIN32)
        LARGE_INTEGER li_size;
     __int64 filesize, offset;
 #else
       off_t filesize, offset;
 #endif

     mbedtls_aes_init( &aes_ctx );
     mbedtls_md_init( &sha_ctx );

     ret = mbedtls_md_setup( &sha_ctx, mbedtls_md_info_from_type( MBEDTLS_MD_SHA256 ), 1 );
     if( ret != 0 )
     {
         mbedtls_printf( "  ! mbedtls_md_setup() returned -0x%04x\n", -ret );
         goto exit;
     }

     /*
      * Parse the command-line arguments.
      */
     if( argc != 5 )
     {
         mbedtls_printf( USAGE );

 #if defined(_WIN32)
         mbedtls_printf( "\n  Press Enter to exit this program.\n" );
         fflush( stdout ); getchar();
 #endif

         goto exit;
     }

     mode = atoi( argv[1] );
     memset( IV,     0, sizeof( IV ) );
     memset( key,    0, sizeof( key ) );
     memset( digest, 0, sizeof( digest ) );
     memset( buffer, 0, sizeof( buffer ) );

     if( mode != MODE_ENCRYPT && mode != MODE_DECRYPT )
     {
         mbedtls_fprintf( stderr, "invalide operation mode\n" );
         goto exit;
     }

     if( strcmp( argv[2], argv[3] ) == 0 )
     {
         mbedtls_fprintf( stderr, "input and output filenames must differ\n" );
         goto exit;
     }

     if( ( fin = fopen( argv[2], "rb" ) ) == NULL )
     {
         mbedtls_fprintf( stderr, "fopen(%s,rb) failed\n", argv[2] );
         goto exit;
     }

     if( ( fout = fopen( argv[3], "wb+" ) ) == NULL )
     {
         mbedtls_fprintf( stderr, "fopen(%s,wb+) failed\n", argv[3] );
         goto exit;
     }

     /*
      * Read the secret key from file or command line
      */
     if( ( fkey = fopen( argv[4], "rb" ) ) != NULL )
     {
         keylen = fread( key, 1, sizeof( key ), fkey );
         fclose( fkey );
     }
     else
     {
         if( memcmp( argv[4], "hex:", 4 ) == 0 )
         {
             p = &argv[4][4];
             keylen = 0;

             while( sscanf( p, "%02X", &n ) > 0 &&
                    keylen < (int) sizeof( key ) )
             {
                 key[keylen++] = (unsigned char) n;
                 p += 2;
             }
         }
         else
         {
             keylen = strlen( argv[4] );

             if( keylen > (int) sizeof( key ) )
                 keylen = (int) sizeof( key );

             memcpy( key, argv[4], keylen );
         }
     }

 #if defined(_WIN32_WCE)
     filesize = fseek( fin, 0L, SEEK_END );
 #else
 #if defined(_WIN32)
     /*
      * Support large files (> 2Gb) on Win32
      */
     li_size.QuadPart = 0;
     li_size.LowPart  =
         SetFilePointer( (HANDLE) _get_osfhandle( _fileno( fin ) ),
                         li_size.LowPart, &li_size.HighPart, FILE_END );

     if( li_size.LowPart == 0xFFFFFFFF && GetLastError() != NO_ERROR )
     {
         mbedtls_fprintf( stderr, "SetFilePointer(0,FILE_END) failed\n" );
         goto exit;
     }

     filesize = li_size.QuadPart;
 #else
     if( ( filesize = lseek( fileno( fin ), 0, SEEK_END ) ) < 0 )
     {
         perror( "lseek" );
         goto exit;
     }
 #endif
 #endif

     if( fseek( fin, 0, SEEK_SET ) < 0 )
     {
         mbedtls_fprintf( stderr, "fseek(0,SEEK_SET) failed\n" );
         goto exit;
     }

     if( mode == MODE_ENCRYPT )
     {
         /*
          * Generate the initialization vector as:
          * IV = SHA-256( filesize || filename )[0..15]
          */
         for( i = 0; i < 8; i++ )
             buffer[i] = (unsigned char)( filesize >> ( i << 3 ) );

         p = argv[2];

         mbedtls_md_starts( &sha_ctx );
         mbedtls_md_update( &sha_ctx, buffer, 8 );
         mbedtls_md_update( &sha_ctx, (unsigned char *) p, strlen( p ) );
         mbedtls_md_finish( &sha_ctx, digest );

         memcpy( IV, digest, 16 );

         /*
          * The last four bits in the IV are actually used
          * to store the file size modulo the AES block size.
          */
         lastn = (int)( filesize & 0x0F );

         IV[15] = (unsigned char)
             ( ( IV[15] & 0xF0 ) | lastn );

         /*
          * Append the IV at the beginning of the output.
          */
         if( fwrite( IV, 1, 16, fout ) != 16 )
         {
             mbedtls_fprintf( stderr, "fwrite(%d bytes) failed\n", 16 );
             goto exit;
         }

         /*
          * Hash the IV and the secret key together 8192 times
          * using the result to setup the AES context and HMAC.
          */
         memset( digest, 0,  32 );
         memcpy( digest, IV, 16 );

         for( i = 0; i < 8192; i++ )
         {
             mbedtls_md_starts( &sha_ctx );
             mbedtls_md_update( &sha_ctx, digest, 32 );
             mbedtls_md_update( &sha_ctx, key, keylen );
             mbedtls_md_finish( &sha_ctx, digest );
         }

         mbedtls_aes_setkey_enc( &aes_ctx, digest, 256 );
         mbedtls_md_hmac_starts( &sha_ctx, digest, 32 );

         /*
          * Encrypt and write the ciphertext.
          */
         for( offset = 0; offset < filesize; offset += 16 )
         {
             n = ( filesize - offset > 16 ) ? 16 : (int)
                 ( filesize - offset );

             if( fread( buffer, 1, n, fin ) != (size_t) n )
             {
                 mbedtls_fprintf( stderr, "fread(%d bytes) failed\n", n );
                 goto exit;
             }

             for( i = 0; i < 16; i++ )
                 buffer[i] = (unsigned char)( buffer[i] ^ IV[i] );

             mbedtls_aes_crypt_ecb( &aes_ctx, MBEDTLS_AES_ENCRYPT, buffer, buffer );
             mbedtls_md_hmac_update( &sha_ctx, buffer, 16 );

             if( fwrite( buffer, 1, 16, fout ) != 16 )
             {
                 mbedtls_fprintf( stderr, "fwrite(%d bytes) failed\n", 16 );
                 goto exit;
             }

             memcpy( IV, buffer, 16 );
         }

         /*
          * Finally write the HMAC.
          */
         mbedtls_md_hmac_finish( &sha_ctx, digest );

         if( fwrite( digest, 1, 32, fout ) != 32 )
         {
             mbedtls_fprintf( stderr, "fwrite(%d bytes) failed\n", 16 );
             goto exit;
         }
     }

     if( mode == MODE_DECRYPT )
     {
         /*
          *  The encrypted file must be structured as follows:
          *
          *        00 .. 15              Initialization Vector
          *        16 .. 31              AES Encrypted Block #1
          *           ..
          *      N*16 .. (N+1)*16 - 1    AES Encrypted Block #N
          *  (N+1)*16 .. (N+1)*16 + 32   HMAC-SHA-256(ciphertext)
          */
         if( filesize < 48 )
         {
             mbedtls_fprintf( stderr, "File too short to be encrypted.\n" );
             goto exit;
         }

         if( ( filesize & 0x0F ) != 0 )
         {
             mbedtls_fprintf( stderr, "File size not a multiple of 16.\n" );
             goto exit;
         }

         /*
          * Subtract the IV + HMAC length.
          */
         filesize -= ( 16 + 32 );

         /*
          * Read the IV and original filesize modulo 16.
          */
         if( fread( buffer, 1, 16, fin ) != 16 )
         {
             mbedtls_fprintf( stderr, "fread(%d bytes) failed\n", 16 );
             goto exit;
         }

         memcpy( IV, buffer, 16 );
         lastn = IV[15] & 0x0F;

         /*
          * Hash the IV and the secret key together 8192 times
          * using the result to setup the AES context and HMAC.
          */
         memset( digest, 0,  32 );
         memcpy( digest, IV, 16 );

         for( i = 0; i < 8192; i++ )
         {
             mbedtls_md_starts( &sha_ctx );
             mbedtls_md_update( &sha_ctx, digest, 32 );
             mbedtls_md_update( &sha_ctx, key, keylen );
             mbedtls_md_finish( &sha_ctx, digest );
         }

         mbedtls_aes_setkey_dec( &aes_ctx, digest, 256 );
         mbedtls_md_hmac_starts( &sha_ctx, digest, 32 );

         /*
          * Decrypt and write the plaintext.
          */
         for( offset = 0; offset < filesize; offset += 16 )
         {
             if( fread( buffer, 1, 16, fin ) != 16 )
             {
                 mbedtls_fprintf( stderr, "fread(%d bytes) failed\n", 16 );
                 goto exit;
             }

             memcpy( tmp, buffer, 16 );

             mbedtls_md_hmac_update( &sha_ctx, buffer, 16 );
             mbedtls_aes_crypt_ecb( &aes_ctx, MBEDTLS_AES_DECRYPT, buffer, buffer );

             for( i = 0; i < 16; i++ )
                 buffer[i] = (unsigned char)( buffer[i] ^ IV[i] );

             memcpy( IV, tmp, 16 );

             n = ( lastn > 0 && offset == filesize - 16 )
                 ? lastn : 16;

             if( fwrite( buffer, 1, n, fout ) != (size_t) n )
             {
                 mbedtls_fprintf( stderr, "fwrite(%d bytes) failed\n", n );
                 goto exit;
             }
         }

         /*
          * Verify the message authentication code.
          */
         mbedtls_md_hmac_finish( &sha_ctx, digest );

         if( fread( buffer, 1, 32, fin ) != 32 )
         {
             mbedtls_fprintf( stderr, "fread(%d bytes) failed\n", 32 );
             goto exit;
         }

         /* Use constant-time buffer comparison */
         diff = 0;
         for( i = 0; i < 32; i++ )
             diff |= digest[i] ^ buffer[i];

         if( diff != 0 )
         {
             mbedtls_fprintf( stderr, "HMAC check failed: wrong key, "
                              "or file corrupted.\n" );
             goto exit;
         }
     }

     exit_code = MBEDTLS_EXIT_SUCCESS;

 exit:
     if( fin )
         fclose( fin );
     if( fout )
         fclose( fout );

     /* Zeroize all command line arguments to also cover
        the case when the user has missed or reordered some,
        in which case the key might not be in argv[4]. */
     for( i = 0; i < (unsigned int) argc; i++ )
         mbedtls_platform_zeroize( argv[i], strlen( argv[i] ) );

     mbedtls_platform_zeroize( IV,     sizeof( IV ) );
     mbedtls_platform_zeroize( key,    sizeof( key ) );
     mbedtls_platform_zeroize( tmp,    sizeof( tmp ) );
     mbedtls_platform_zeroize( buffer, sizeof( buffer ) );
     mbedtls_platform_zeroize( digest, sizeof( digest ) );

     mbedtls_aes_free( &aes_ctx );
     mbedtls_md_free( &sha_ctx );

     return( exit_code );
 }
 #endif /* MBEDTLS_AES_C && MBEDTLS_SHA256_C && MBEDTLS_FS_IO */
	/*
	* AES-256 file encryption program
	*
	* Copyright (C) 2006-2015, ARM Limited, All Rights Reserved
	* SPDX-License-Identifier: Apache-2.0
	*
	* Licensed under the Apache License, Version 2.0 (the "License"); you may
	* not use this file except in compliance with the License.
	* You may obtain a copy of the License at
	*
	* http://www.apache.org/licenses/LICENSE-2.0
	*
	* Unless required by applicable law or agreed to in writing, software
	* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
	* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	* See the License for the specific language governing permissions and
	* limitations under the License.
	*
	* This file is part of mbed TLS (https://tls.mbed.org)
	*/

	/* Enable definition of fileno() even when compiling with -std=c99. Must be
	* set before config.h, which pulls in glibc's features.h indirectly.
	* Harmless on other platforms. */
	#define _POSIX_C_SOURCE 1

	#if !defined(MBEDTLS_CONFIG_FILE)
	#include "mbedtls/config.h"
	#else
	#include MBEDTLS_CONFIG_FILE
	#endif

	#if defined(MBEDTLS_PLATFORM_C)
	#include "mbedtls/platform.h"
	#else
	#include <stdio.h>
	#include <stdlib.h>
	#define mbedtls_fprintf fprintf
	#define mbedtls_printf printf
	#define mbedtls_exit exit
	#define MBEDTLS_EXIT_SUCCESS EXIT_SUCCESS
	#define MBEDTLS_EXIT_FAILURE EXIT_FAILURE
	#endif /* MBEDTLS_PLATFORM_C */

	#include "mbedtls/aes.h"
	#include "mbedtls/md.h"
	#include "mbedtls/platform_util.h"

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

	#if defined(_WIN32)
	#include <windows.h>
	#if !defined(_WIN32_WCE)
	#include <io.h>
	#endif
	#else
	#include <sys/types.h>
	#include <unistd.h>
	#endif

	#define MODE_ENCRYPT 0
	#define MODE_DECRYPT 1

	#define USAGE \
	"\n aescrypt2 <mode> <input filename> <output filename> <key>\n" \
	"\n <mode>: 0 = encrypt, 1 = decrypt\n" \
	"\n example: aescrypt2 0 file file.aes hex:E76B2413958B00E193\n" \
	"\n"

	#if !defined(MBEDTLS_AES_C) \|\| !defined(MBEDTLS_SHA256_C) \|\| \
	!defined(MBEDTLS_FS_IO) \|\| !defined(MBEDTLS_MD_C)
	int main( void )
	{
	mbedtls_printf("MBEDTLS_AES_C and/or MBEDTLS_SHA256_C "
	"and/or MBEDTLS_FS_IO and/or MBEDTLS_MD_C "
	"not defined.\n");
	return( 0 );
	}
	#else


	int main( int argc, char *argv[] )
	{
	int ret = 0;
	int exit_code = MBEDTLS_EXIT_FAILURE;

	unsigned int i, n;
	int mode, lastn;
	size_t keylen;
	FILE fkey, fin = NULL, *fout = NULL;

	char *p;

	unsigned char IV[16];
	unsigned char tmp[16];
	unsigned char key[512];
	unsigned char digest[64];
	unsigned char buffer[1024];
	unsigned char diff;

	mbedtls_aes_context aes_ctx;
	mbedtls_md_context_t sha_ctx;

	#if defined(_WIN32_WCE)
	long filesize, offset;
	#elif defined(_WIN32)
	LARGE_INTEGER li_size;
	__int64 filesize, offset;
	#else
	off_t filesize, offset;
	#endif

	mbedtls_aes_init( &aes_ctx );
	mbedtls_md_init( &sha_ctx );

	ret = mbedtls_md_setup( &sha_ctx, mbedtls_md_info_from_type( MBEDTLS_MD_SHA256 ), 1 );
	if( ret != 0 )
	{
	mbedtls_printf( " ! mbedtls_md_setup() returned -0x%04x\n", -ret );
	goto exit;
	}

	/*
	* Parse the command-line arguments.
	*/
	if( argc != 5 )
	{
	mbedtls_printf( USAGE );

	#if defined(_WIN32)
	mbedtls_printf( "\n Press Enter to exit this program.\n" );
	fflush( stdout ); getchar();
	#endif

	goto exit;
	}

	mode = atoi( argv[1] );
	memset( IV, 0, sizeof( IV ) );
	memset( key, 0, sizeof( key ) );
	memset( digest, 0, sizeof( digest ) );
	memset( buffer, 0, sizeof( buffer ) );

	if( mode != MODE_ENCRYPT && mode != MODE_DECRYPT )
	{
	mbedtls_fprintf( stderr, "invalide operation mode\n" );
	goto exit;
	}

	if( strcmp( argv[2], argv[3] ) == 0 )
	{
	mbedtls_fprintf( stderr, "input and output filenames must differ\n" );
	goto exit;
	}

	if( ( fin = fopen( argv[2], "rb" ) ) == NULL )
	{
	mbedtls_fprintf( stderr, "fopen(%s,rb) failed\n", argv[2] );
	goto exit;
	}

	if( ( fout = fopen( argv[3], "wb+" ) ) == NULL )
	{
	mbedtls_fprintf( stderr, "fopen(%s,wb+) failed\n", argv[3] );
	goto exit;
	}

	/*
	* Read the secret key from file or command line
	*/
	if( ( fkey = fopen( argv[4], "rb" ) ) != NULL )
	{
	keylen = fread( key, 1, sizeof( key ), fkey );
	fclose( fkey );
	}
	else
	{
	if( memcmp( argv[4], "hex:", 4 ) == 0 )
	{
	p = &argv[4][4];
	keylen = 0;

	while( sscanf( p, "%02X", &n ) > 0 &&
	keylen < (int) sizeof( key ) )
	{
	key[keylen++] = (unsigned char) n;
	p += 2;
	}
	}
	else
	{
	keylen = strlen( argv[4] );

	if( keylen > (int) sizeof( key ) )
	keylen = (int) sizeof( key );

	memcpy( key, argv[4], keylen );
	}
	}

	#if defined(_WIN32_WCE)
	filesize = fseek( fin, 0L, SEEK_END );
	#else
	#if defined(_WIN32)
	/*
	* Support large files (> 2Gb) on Win32
	*/
	li_size.QuadPart = 0;
	li_size.LowPart =
	SetFilePointer( (HANDLE) _get_osfhandle( _fileno( fin ) ),
	li_size.LowPart, &li_size.HighPart, FILE_END );

	if( li_size.LowPart == 0xFFFFFFFF && GetLastError() != NO_ERROR )
	{
	mbedtls_fprintf( stderr, "SetFilePointer(0,FILE_END) failed\n" );
	goto exit;
	}

	filesize = li_size.QuadPart;
	#else
	if( ( filesize = lseek( fileno( fin ), 0, SEEK_END ) ) < 0 )
	{
	perror( "lseek" );
	goto exit;
	}
	#endif
	#endif

	if( fseek( fin, 0, SEEK_SET ) < 0 )
	{
	mbedtls_fprintf( stderr, "fseek(0,SEEK_SET) failed\n" );
	goto exit;
	}

	if( mode == MODE_ENCRYPT )
	{
	/*
	* Generate the initialization vector as:
	* IV = SHA-256( filesize \|\| filename )[0..15]
	*/
	for( i = 0; i < 8; i++ )
	buffer[i] = (unsigned char)( filesize >> ( i << 3 ) );

	p = argv[2];

	mbedtls_md_starts( &sha_ctx );
	mbedtls_md_update( &sha_ctx, buffer, 8 );
	mbedtls_md_update( &sha_ctx, (unsigned char *) p, strlen( p ) );
	mbedtls_md_finish( &sha_ctx, digest );

	memcpy( IV, digest, 16 );

	/*
	* The last four bits in the IV are actually used
	* to store the file size modulo the AES block size.
	*/
	lastn = (int)( filesize & 0x0F );

	IV[15] = (unsigned char)
	( ( IV[15] & 0xF0 ) \| lastn );

	/*
	* Append the IV at the beginning of the output.
	*/
	if( fwrite( IV, 1, 16, fout ) != 16 )
	{
	mbedtls_fprintf( stderr, "fwrite(%d bytes) failed\n", 16 );
	goto exit;
	}

	/*
	* Hash the IV and the secret key together 8192 times
	* using the result to setup the AES context and HMAC.
	*/
	memset( digest, 0, 32 );
	memcpy( digest, IV, 16 );

	for( i = 0; i < 8192; i++ )
	{
	mbedtls_md_starts( &sha_ctx );
	mbedtls_md_update( &sha_ctx, digest, 32 );
	mbedtls_md_update( &sha_ctx, key, keylen );
	mbedtls_md_finish( &sha_ctx, digest );
	}

	mbedtls_aes_setkey_enc( &aes_ctx, digest, 256 );
	mbedtls_md_hmac_starts( &sha_ctx, digest, 32 );

	/*
	* Encrypt and write the ciphertext.
	*/
	for( offset = 0; offset < filesize; offset += 16 )
	{
	n = ( filesize - offset > 16 ) ? 16 : (int)
	( filesize - offset );

	if( fread( buffer, 1, n, fin ) != (size_t) n )
	{
	mbedtls_fprintf( stderr, "fread(%d bytes) failed\n", n );
	goto exit;
	}

	for( i = 0; i < 16; i++ )
	buffer[i] = (unsigned char)( buffer[i] ^ IV[i] );

	mbedtls_aes_crypt_ecb( &aes_ctx, MBEDTLS_AES_ENCRYPT, buffer, buffer );
	mbedtls_md_hmac_update( &sha_ctx, buffer, 16 );

	if( fwrite( buffer, 1, 16, fout ) != 16 )
	{
	mbedtls_fprintf( stderr, "fwrite(%d bytes) failed\n", 16 );
	goto exit;
	}

	memcpy( IV, buffer, 16 );
	}

	/*
	* Finally write the HMAC.
	*/
	mbedtls_md_hmac_finish( &sha_ctx, digest );

	if( fwrite( digest, 1, 32, fout ) != 32 )
	{
	mbedtls_fprintf( stderr, "fwrite(%d bytes) failed\n", 16 );
	goto exit;
	}
	}

	if( mode == MODE_DECRYPT )
	{
	/*
	* The encrypted file must be structured as follows:
	*
	* 00 .. 15 Initialization Vector
	* 16 .. 31 AES Encrypted Block #1
	* ..
	* N16 .. (N+1)16 - 1 AES Encrypted Block #N
	* (N+1)16 .. (N+1)16 + 32 HMAC-SHA-256(ciphertext)
	*/
	if( filesize < 48 )
	{
	mbedtls_fprintf( stderr, "File too short to be encrypted.\n" );
	goto exit;
	}

	if( ( filesize & 0x0F ) != 0 )
	{
	mbedtls_fprintf( stderr, "File size not a multiple of 16.\n" );
	goto exit;
	}

	/*
	* Subtract the IV + HMAC length.
	*/
	filesize -= ( 16 + 32 );

	/*
	* Read the IV and original filesize modulo 16.
	*/
	if( fread( buffer, 1, 16, fin ) != 16 )
	{
	mbedtls_fprintf( stderr, "fread(%d bytes) failed\n", 16 );
	goto exit;
	}

	memcpy( IV, buffer, 16 );
	lastn = IV[15] & 0x0F;

	/*
	* Hash the IV and the secret key together 8192 times
	* using the result to setup the AES context and HMAC.
	*/
	memset( digest, 0, 32 );
	memcpy( digest, IV, 16 );

	for( i = 0; i < 8192; i++ )
	{
	mbedtls_md_starts( &sha_ctx );
	mbedtls_md_update( &sha_ctx, digest, 32 );
	mbedtls_md_update( &sha_ctx, key, keylen );
	mbedtls_md_finish( &sha_ctx, digest );
	}

	mbedtls_aes_setkey_dec( &aes_ctx, digest, 256 );
	mbedtls_md_hmac_starts( &sha_ctx, digest, 32 );

	/*
	* Decrypt and write the plaintext.
	*/
	for( offset = 0; offset < filesize; offset += 16 )
	{
	if( fread( buffer, 1, 16, fin ) != 16 )
	{
	mbedtls_fprintf( stderr, "fread(%d bytes) failed\n", 16 );
	goto exit;
	}

	memcpy( tmp, buffer, 16 );

	mbedtls_md_hmac_update( &sha_ctx, buffer, 16 );
	mbedtls_aes_crypt_ecb( &aes_ctx, MBEDTLS_AES_DECRYPT, buffer, buffer );

	for( i = 0; i < 16; i++ )
	buffer[i] = (unsigned char)( buffer[i] ^ IV[i] );

	memcpy( IV, tmp, 16 );

	n = ( lastn > 0 && offset == filesize - 16 )
	? lastn : 16;

	if( fwrite( buffer, 1, n, fout ) != (size_t) n )
	{
	mbedtls_fprintf( stderr, "fwrite(%d bytes) failed\n", n );
	goto exit;
	}
	}

	/*
	* Verify the message authentication code.
	*/
	mbedtls_md_hmac_finish( &sha_ctx, digest );

	if( fread( buffer, 1, 32, fin ) != 32 )
	{
	mbedtls_fprintf( stderr, "fread(%d bytes) failed\n", 32 );
	goto exit;
	}

	/* Use constant-time buffer comparison */
	diff = 0;
	for( i = 0; i < 32; i++ )
	diff \|= digest[i] ^ buffer[i];

	if( diff != 0 )
	{
	mbedtls_fprintf( stderr, "HMAC check failed: wrong key, "
	"or file corrupted.\n" );
	goto exit;
	}
	}

	exit_code = MBEDTLS_EXIT_SUCCESS;

	exit:
	if( fin )
	fclose( fin );
	if( fout )
	fclose( fout );

	/* Zeroize all command line arguments to also cover
	the case when the user has missed or reordered some,
	in which case the key might not be in argv[4]. */
	for( i = 0; i < (unsigned int) argc; i++ )
	mbedtls_platform_zeroize( argv[i], strlen( argv[i] ) );

	mbedtls_platform_zeroize( IV, sizeof( IV ) );
	mbedtls_platform_zeroize( key, sizeof( key ) );
	mbedtls_platform_zeroize( tmp, sizeof( tmp ) );
	mbedtls_platform_zeroize( buffer, sizeof( buffer ) );
	mbedtls_platform_zeroize( digest, sizeof( digest ) );

	mbedtls_aes_free( &aes_ctx );
	mbedtls_md_free( &sha_ctx );

	return( exit_code );
	}
	#endif /* MBEDTLS_AES_C && MBEDTLS_SHA256_C && MBEDTLS_FS_IO */