diff --git a/encrypt.cpp b/encrypt.cpp
index 57e2b5d..b2e0af7 100755
--- a/encrypt.cpp
+++ b/encrypt.cpp
@@ -11,8 +11,11 @@
 //static uint64_t seq=1;
 
 static int8_t zero_iv[]={0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,   0,0,0,0};//this prog use zero iv,you should make sure first block of data contains a random/nonce data
-
-
+/****
+ * important!
+ * why zero iv + nonce first data block is secure?
+ * https://crypto.stackexchange.com/questions/5421/using-cbc-with-a-fixed-iv-and-a-random-first-plaintext-block
+****/
 unordered_map<int, const char *> auth_mode_tostring = {{auth_none, "none"}, {auth_md5, "md5"}, {auth_crc32, "crc32"},{auth_simple,"simple"}};
 unordered_map<int, const char *> cipher_mode_tostring={{cipher_none,"none"},{cipher_aes128cbc,"aes128cbc"},{cipher_xor,"xor"}};