diff --git a/cmake_targets/tools/build_hss b/cmake_targets/tools/build_hss
index a7ec8b20fad8a394bd65b8305006a7c67e351b25..06b26a20fd0d627bec2a02d1ebcf38ddb4a6e7c3 100755
--- a/cmake_targets/tools/build_hss
+++ b/cmake_targets/tools/build_hss
@@ -60,6 +60,8 @@ function help()
   echo_error "                                            If not specified, default is 11111111111111111111111111111111 if operator ckey is not specified also."
   echo_error "  -K, --operator-ckey            ciph. key  Operator ciphered key of the HSS (Could be 8E27B6AF0E692E750F32667A3B14605D=OPC(11111111111111111111111111111111))."
   echo_error "                                            ( OPC()=RijndaelEncrypt(operator-key) Xor operator-key, LTE-K (prov database) scheduled in Rijndael algo before RijndaelEncrypt)."
+  echo_error "                                            Note that you can have the RijndaelEncrypt() at http://extranet.cryptomathic.com/aescalc or"
+  echo_error "                                                                                         at http://www.hanewin.net/encrypt/aes/aes-test.htm."
   echo_error "  -m, --connect-to-mme           fqdn       MME act as a S6A server, HSS as a client (reversed situation but allows MME and HSS be on the same host) ."
   echo_error "  -r, --realm                    realm      Realm of the HSS (optional parameter)."
   echo_error "  -s, --transport-sctp-only                 Diameter use SCTP (TCP disabled)."