There are several encryption libraries in this forum, it's quite confusing, I was using SS_AESEncryption, B4XEncryption, now I'm going for Base64 and Encryption Library, https://www.b4x.com/android/forum/threads/base64-and-encryption-library.6839/
But it's from a 2010 post, rather old. It was easier on B4i , just use the integrated library.