diff --git a/library/cipher_wrap.c b/library/cipher_wrap.c
index 490f981..59d77df 100644
--- a/library/cipher_wrap.c
+++ b/library/cipher_wrap.c
@@ -70,7 +70,7 @@
 #include "mbedtls/platform.h"
 #else
 #include <stdlib.h>
-#define mbedtls_malloc     malloc
+#define mbedtls_calloc    calloc
 #define mbedtls_free       free
 #endif
 
@@ -78,7 +78,7 @@
 /* shared by all GCM ciphers */
 static void *gcm_ctx_alloc( void )
 {
-    return mbedtls_malloc( sizeof( mbedtls_gcm_context ) );
+    return mbedtls_calloc( 1, sizeof( mbedtls_gcm_context ) );
 }
 
 static void gcm_ctx_free( void *ctx )
@@ -92,7 +92,7 @@
 /* shared by all CCM ciphers */
 static void *ccm_ctx_alloc( void )
 {
-    return mbedtls_malloc( sizeof( mbedtls_ccm_context ) );
+    return mbedtls_calloc( 1, sizeof( mbedtls_ccm_context ) );
 }
 
 static void ccm_ctx_free( void *ctx )
@@ -153,7 +153,7 @@
 
 static void * aes_ctx_alloc( void )
 {
-    mbedtls_aes_context *aes = mbedtls_malloc( sizeof( mbedtls_aes_context ) );
+    mbedtls_aes_context *aes = mbedtls_calloc( 1, sizeof( mbedtls_aes_context ) );
 
     if( aes == NULL )
         return( NULL );
@@ -510,7 +510,7 @@
 static void * camellia_ctx_alloc( void )
 {
     mbedtls_camellia_context *ctx;
-    ctx = mbedtls_malloc( sizeof( mbedtls_camellia_context ) );
+    ctx = mbedtls_calloc( 1, sizeof( mbedtls_camellia_context ) );
 
     if( ctx == NULL )
         return( NULL );
@@ -897,7 +897,7 @@
 
 static void * des_ctx_alloc( void )
 {
-    mbedtls_des_context *des = mbedtls_malloc( sizeof( mbedtls_des_context ) );
+    mbedtls_des_context *des = mbedtls_calloc( 1, sizeof( mbedtls_des_context ) );
 
     if( des == NULL )
         return( NULL );
@@ -916,7 +916,7 @@
 static void * des3_ctx_alloc( void )
 {
     mbedtls_des3_context *des3;
-    des3 = mbedtls_malloc( sizeof( mbedtls_des3_context ) );
+    des3 = mbedtls_calloc( 1, sizeof( mbedtls_des3_context ) );
 
     if( des3 == NULL )
         return( NULL );
@@ -1115,7 +1115,7 @@
 static void * blowfish_ctx_alloc( void )
 {
     mbedtls_blowfish_context *ctx;
-    ctx = mbedtls_malloc( sizeof( mbedtls_blowfish_context ) );
+    ctx = mbedtls_calloc( 1, sizeof( mbedtls_blowfish_context ) );
 
     if( ctx == NULL )
         return( NULL );
@@ -1225,7 +1225,7 @@
 static void * arc4_ctx_alloc( void )
 {
     mbedtls_arc4_context *ctx;
-    ctx = mbedtls_malloc( sizeof( mbedtls_arc4_context ) );
+    ctx = mbedtls_calloc( 1, sizeof( mbedtls_arc4_context ) );
 
     if( ctx == NULL )
         return( NULL );