diff --git a/programs/aes/crypt_and_hash.c b/programs/aes/crypt_and_hash.c
index 9ff5351..74ea88c 100644
--- a/programs/aes/crypt_and_hash.c
+++ b/programs/aes/crypt_and_hash.c
@@ -365,7 +365,11 @@
             goto exit;
         }
 
-        mbedtls_md_hmac_starts( &md_ctx, digest, 32 );
+        if( mbedtls_md_hmac_starts( &md_ctx, digest, 32 ) != 0 )
+        {
+            mbedtls_fprintf( stderr, "mbedtls_md_hmac_starts() returned error\n" );
+            goto exit;
+        }
 
         /*
          * Encrypt and write the ciphertext.
@@ -387,7 +391,11 @@
                 goto exit;
             }
 
-            mbedtls_md_hmac_update( &md_ctx, output, olen );
+            if( mbedtls_md_hmac_update( &md_ctx, output, olen ) != 0 )
+            {
+                mbedtls_fprintf( stderr, "mbedtls_md_hmac_update() returned error\n" );
+                goto exit;
+            }
 
             if( fwrite( output, 1, olen, fout ) != olen )
             {
@@ -401,7 +409,11 @@
             mbedtls_fprintf( stderr, "mbedtls_cipher_finish() returned error\n" );
             goto exit;
         }
-        mbedtls_md_hmac_update( &md_ctx, output, olen );
+        if( mbedtls_md_hmac_update( &md_ctx, output, olen ) != 0 )
+        {
+            mbedtls_fprintf( stderr, "mbedtls_md_hmac_update() returned error\n" );
+            goto exit;
+        }
 
         if( fwrite( output, 1, olen, fout ) != olen )
         {
@@ -412,7 +424,11 @@
         /*
          * Finally write the HMAC.
          */
-        mbedtls_md_hmac_finish( &md_ctx, digest );
+        if( mbedtls_md_hmac_finish( &md_ctx, digest ) != 0 )
+        {
+            mbedtls_fprintf( stderr, "mbedtls_md_hmac_finish() returned error\n" );
+            goto exit;
+        }
 
         if( fwrite( digest, 1, mbedtls_md_get_size( md_info ), fout ) != mbedtls_md_get_size( md_info ) )
         {
@@ -481,10 +497,26 @@
 
         for( i = 0; i < 8192; i++ )
         {
-            mbedtls_md_starts( &md_ctx );
-            mbedtls_md_update( &md_ctx, digest, 32 );
-            mbedtls_md_update( &md_ctx, key, keylen );
-            mbedtls_md_finish( &md_ctx, digest );
+            if( mbedtls_md_starts( &md_ctx ) != 0 )
+            {
+                mbedtls_fprintf( stderr, "mbedtls_md_starts() returned error\n" );
+                goto exit;
+            }
+            if( mbedtls_md_update( &md_ctx, digest, 32 ) != 0 )
+            {
+                mbedtls_fprintf( stderr, "mbedtls_md_update() returned error\n" );
+                goto exit;
+            }
+            if( mbedtls_md_update( &md_ctx, key, keylen ) != 0 )
+            {
+                mbedtls_fprintf( stderr, "mbedtls_md_update() returned error\n" );
+                goto exit;
+            }
+            if( mbedtls_md_finish( &md_ctx, digest ) != 0 )
+            {
+                mbedtls_fprintf( stderr, "mbedtls_md_finish() returned error\n" );
+                goto exit;
+            }
         }
 
         if( mbedtls_cipher_setkey( &cipher_ctx,
@@ -508,7 +540,11 @@
             goto exit;
         }
 
-        mbedtls_md_hmac_starts( &md_ctx, digest, 32 );
+        if( mbedtls_md_hmac_starts( &md_ctx, digest, 32 ) != 0 )
+        {
+            mbedtls_fprintf( stderr, "mbedtls_md_hmac_starts() returned error\n" );
+            goto exit;
+        }
 
         /*
          * Decrypt and write the plaintext.
@@ -525,7 +561,11 @@
                 goto exit;
             }
 
-            mbedtls_md_hmac_update( &md_ctx, buffer, ilen );
+            if( mbedtls_md_hmac_update( &md_ctx, buffer, ilen ) != 0 )
+            {
+                mbedtls_fprintf( stderr, "mbedtls_md_hmac_update() returned error\n" );
+                goto exit;
+            }
             if( mbedtls_cipher_update( &cipher_ctx, buffer, ilen, output,
                                        &olen ) != 0 )
             {
@@ -543,7 +583,11 @@
         /*
          * Verify the message authentication code.
          */
-        mbedtls_md_hmac_finish( &md_ctx, digest );
+        if( mbedtls_md_hmac_finish( &md_ctx, digest ) != 0 )
+        {
+            mbedtls_fprintf( stderr, "mbedtls_md_hmac_finish() returned error\n" );
+            goto exit;
+        }
 
         if( fread( buffer, 1, mbedtls_md_get_size( md_info ), fin ) != mbedtls_md_get_size( md_info ) )
         {
@@ -566,7 +610,11 @@
         /*
          * Write the final block of data
          */
-        mbedtls_cipher_finish( &cipher_ctx, output, &olen );
+        if( mbedtls_cipher_finish( &cipher_ctx, output, &olen ) != 0 )
+        {
+            mbedtls_fprintf( stderr, "mbedtls_cipher_finish() returned error\n" );
+            goto exit;
+        }
 
         if( fwrite( output, 1, olen, fout ) != olen )
         {