diff --git a/library/des.c b/library/des.c
index 65f5681..c56d4d4 100644
--- a/library/des.c
+++ b/library/des.c
@@ -635,7 +635,6 @@
                     const unsigned char *input,
                     unsigned char *output )
 {
-    int i;
     int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
     unsigned char temp[8];
 
@@ -646,8 +645,7 @@
     {
         while( length > 0 )
         {
-            for( i = 0; i < 8; i++ )
-                output[i] = (unsigned char)( input[i] ^ iv[i] );
+            mbedtls_xor( output, input, iv, 8 );
 
             ret = mbedtls_des_crypt_ecb( ctx, output, output );
             if( ret != 0 )
@@ -668,8 +666,7 @@
             if( ret != 0 )
                 goto exit;
 
-            for( i = 0; i < 8; i++ )
-                output[i] = (unsigned char)( output[i] ^ iv[i] );
+            mbedtls_xor( output, output, iv, 8 );
 
             memcpy( iv, temp, 8 );
 
@@ -741,7 +738,6 @@
                      const unsigned char *input,
                      unsigned char *output )
 {
-    int i;
     int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
     unsigned char temp[8];
 
@@ -752,8 +748,7 @@
     {
         while( length > 0 )
         {
-            for( i = 0; i < 8; i++ )
-                output[i] = (unsigned char)( input[i] ^ iv[i] );
+            mbedtls_xor( output, input, iv, 8 );
 
             ret = mbedtls_des3_crypt_ecb( ctx, output, output );
             if( ret != 0 )
@@ -774,8 +769,7 @@
             if( ret != 0 )
                 goto exit;
 
-            for( i = 0; i < 8; i++ )
-                output[i] = (unsigned char)( output[i] ^ iv[i] );
+            mbedtls_xor( output, output, iv, 8 );
 
             memcpy( iv, temp, 8 );