- NSData is automatically bridged to Data in Swift, but it does not mean extension for Data is available in NSData. that is the truth. I will try it and thank you for help.

OK. Thanks for your help. @OOPer In Swift code, there is AESEncrypt method extension for Data in Data+AES.swift class. extension Data {       func AES128Encrypt() throws - Data { ...... } In Objective-C code, I need to call the AESEncrypt method for resultData. But resultData cannot call the AES128Encrypt method. NSData *aesEncryptData = [resultData AES128Encrypt]; When I add @objc in swift extension method, It's showing "@objc can only be used with members of classes, @objc protocols, and concrete extensions of classes".