Fix for #441 - crypt and hash gcm (#546)
* Fix crypt_and_hash to support decrypting GCM encrypted files
* Fix documentation in crypt_and_hash for the generic case
* Remove unused lastn from crypt_and_hash
lastn is not used with the cipher layer as it already provides padding
and understanding of length of the original data.
diff --git a/programs/aes/crypt_and_hash.c b/programs/aes/crypt_and_hash.c
index 102144e..d889245 100644
--- a/programs/aes/crypt_and_hash.c
+++ b/programs/aes/crypt_and_hash.c
@@ -2,7 +2,7 @@
* \brief Generic file encryption program using generic wrappers for configured
* security.
*
- * Copyright (C) 2006-2015, ARM Limited, All Rights Reserved
+ * Copyright (C) 2006-2016, ARM Limited, All Rights Reserved
* SPDX-License-Identifier: Apache-2.0
*
* Licensed under the Apache License, Version 2.0 (the "License"); you may
@@ -74,7 +74,7 @@
int main( int argc, char *argv[] )
{
int ret = 1, i, n;
- int mode, lastn;
+ int mode;
size_t keylen, ilen, olen;
FILE *fkey, *fin = NULL, *fout = NULL;
@@ -259,7 +259,7 @@
{
/*
* Generate the initialization vector as:
- * IV = SHA-256( filesize || filename )[0..15]
+ * IV = MD( filesize || filename )[0..15]
*/
for( i = 0; i < 8; i++ )
buffer[i] = (unsigned char)( filesize >> ( i << 3 ) );
@@ -274,15 +274,6 @@
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 )
@@ -388,10 +379,10 @@
* The encrypted file must be structured as follows:
*
* 00 .. 15 Initialization Vector
- * 16 .. 31 AES Encrypted Block #1
+ * 16 .. 31 Encrypted Block #1
* ..
- * N*16 .. (N+1)*16 - 1 AES Encrypted Block #N
- * (N+1)*16 .. (N+1)*16 + 32 HMAC-SHA-256(ciphertext)
+ * N*16 .. (N+1)*16 - 1 Encrypted Block #N
+ * (N+1)*16 .. (N+1)*16 + n Hash(ciphertext)
*/
if( filesize < 16 + mbedtls_md_get_size( md_info ) )
{
@@ -399,7 +390,17 @@
goto exit;
}
- if( ( ( filesize - mbedtls_md_get_size( md_info ) ) %
+ if( mbedtls_cipher_get_block_size( &cipher_ctx ) == 0 )
+ {
+ mbedtls_fprintf( stderr, "Invalid cipher block size: 0. \n" );
+ goto exit;
+ }
+
+ /*
+ * Check the file size.
+ */
+ if( cipher_info->mode != MBEDTLS_MODE_GCM &&
+ ( ( filesize - mbedtls_md_get_size( md_info ) ) %
mbedtls_cipher_get_block_size( &cipher_ctx ) ) != 0 )
{
mbedtls_fprintf( stderr, "File content not a multiple of the block size (%d).\n",
@@ -422,7 +423,6 @@
}
memcpy( IV, buffer, 16 );
- lastn = IV[15] & 0x0F;
/*
* Hash the IV and the secret key together 8192 times
@@ -467,18 +467,19 @@
*/
for( offset = 0; offset < filesize; offset += mbedtls_cipher_get_block_size( &cipher_ctx ) )
{
- if( fread( buffer, 1, mbedtls_cipher_get_block_size( &cipher_ctx ), fin ) !=
- (size_t) mbedtls_cipher_get_block_size( &cipher_ctx ) )
+ ilen = ( (unsigned int) filesize - offset > mbedtls_cipher_get_block_size( &cipher_ctx ) ) ?
+ mbedtls_cipher_get_block_size( &cipher_ctx ) : (unsigned int) ( filesize - offset );
+
+ if( fread( buffer, 1, ilen, fin ) != ilen )
{
mbedtls_fprintf( stderr, "fread(%d bytes) failed\n",
mbedtls_cipher_get_block_size( &cipher_ctx ) );
goto exit;
}
- mbedtls_md_hmac_update( &md_ctx, buffer, mbedtls_cipher_get_block_size( &cipher_ctx ) );
- if( mbedtls_cipher_update( &cipher_ctx, buffer,
- mbedtls_cipher_get_block_size( &cipher_ctx ),
- output, &olen ) != 0 )
+ mbedtls_md_hmac_update( &md_ctx, buffer, ilen );
+ if( mbedtls_cipher_update( &cipher_ctx, buffer, ilen, output,
+ &olen ) != 0 )
{
mbedtls_fprintf( stderr, "mbedtls_cipher_update() returned error\n" );
goto exit;