From 6a74b2f687c53e9f2c43f044511f0d87281914a3 Mon Sep 17 00:00:00 2001
From: Hanno Becker <hanno.becker@arm.com>
Date: Fri, 12 Oct 2018 16:46:37 +0100
Subject: [PATCH] Zeroize sensitive data in aescrypt2 and crypt_and_hash
 examples

This commit replaces multiple `memset()` calls in the example
programs aes/aescrypt2.c and aes/crypt_and_hash.c by calls to
the reliable zeroization function `mbedtls_zeroize()`.

While not a security issue because the code is in the example
programs, it's bad practice and should be fixed.
---
 programs/aes/aescrypt2.c      | 18 ++++++++++++------
 programs/aes/crypt_and_hash.c | 18 ++++++++++++------
 2 files changed, 24 insertions(+), 12 deletions(-)

diff --git a/programs/aes/aescrypt2.c b/programs/aes/aescrypt2.c
index de9d422cd..939c927a9 100644
--- a/programs/aes/aescrypt2.c
+++ b/programs/aes/aescrypt2.c
@@ -69,6 +69,12 @@ int main( void )
     return( 0 );
 }
 #else
+
+/* Implementation that should never be optimized out by the compiler */
+static void mbedtls_zeroize( void *v, size_t n ) {
+    volatile unsigned char *p = v; while( n-- ) *p++ = 0;
+}
+
 int main( int argc, char *argv[] )
 {
     int ret = 1;
@@ -441,13 +447,13 @@ exit:
        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 < argc; i++ )
-        memset( argv[i], 0, strlen( argv[i] ) );
+        mbedtls_zeroize( argv[i], strlen( argv[i] ) );
 
-    memset( IV,     0, sizeof( IV ) );
-    memset( key,    0, sizeof( key ) );
-    memset( tmp,    0, sizeof( tmp ) );
-    memset( buffer, 0, sizeof( buffer ) );
-    memset( digest, 0, sizeof( digest ) );
+    mbedtls_zeroize( IV,     sizeof( IV ) );
+    mbedtls_zeroize( key,    sizeof( key ) );
+    mbedtls_zeroize( tmp,    sizeof( tmp ) );
+    mbedtls_zeroize( buffer, sizeof( buffer ) );
+    mbedtls_zeroize( digest, sizeof( digest ) );
 
     mbedtls_aes_free( &aes_ctx );
     mbedtls_md_free( &sha_ctx );
diff --git a/programs/aes/crypt_and_hash.c b/programs/aes/crypt_and_hash.c
index 5885bdb5a..caad604a8 100644
--- a/programs/aes/crypt_and_hash.c
+++ b/programs/aes/crypt_and_hash.c
@@ -71,6 +71,12 @@ int main( void )
     return( 0 );
 }
 #else
+
+/* Implementation that should never be optimized out by the compiler */
+static void mbedtls_zeroize( void *v, size_t n ) {
+    volatile unsigned char *p = v; while( n-- ) *p++ = 0;
+}
+
 int main( int argc, char *argv[] )
 {
     int ret = 1, i, n;
@@ -533,13 +539,13 @@ exit:
        the case when the user has missed or reordered some,
        in which case the key might not be in argv[6]. */
     for( i = 0; i < argc; i++ )
-        memset( argv[i], 0, strlen( argv[i] ) );
+        mbedtls_zeroize( argv[i], strlen( argv[i] ) );
 
-    memset( IV,     0, sizeof( IV ) );
-    memset( key,    0, sizeof( key ) );
-    memset( buffer, 0, sizeof( buffer ) );
-    memset( output, 0, sizeof( output ) );
-    memset( digest, 0, sizeof( digest ) );
+    mbedtls_zeroize( IV,     sizeof( IV ) );
+    mbedtls_zeroize( key,    sizeof( key ) );
+    mbedtls_zeroize( buffer, sizeof( buffer ) );
+    mbedtls_zeroize( output, sizeof( output ) );
+    mbedtls_zeroize( digest, sizeof( digest ) );
 
     mbedtls_cipher_free( &cipher_ctx );
     mbedtls_md_free( &md_ctx );