diff --git a/src/crypto/crypto.c b/src/crypto/crypto.c
index 50419d0..476e1c9 100644
--- a/src/crypto/crypto.c
+++ b/src/crypto/crypto.c
@@ -1,3 +1,6 @@
+// based on:
+// https://github.com/vedantk/gcrypt-example/blob/master/gcry.cc
+
 #include "crypto.h"
 
 #include <stdio.h>