Decompiling Java code

I have a .jar file, which is a N okia application. This application is sending/receiving data via a web service. The problem is that they encrypt data before sending data and after receiving it. The .jar file can be decompiled but the code is obfuscated, class names is a,b,c,d,e, etc.. I don't need full source code, but just the code that decrypts sent and received data so that I can use the same web service. I will provide interested bidders with the .jar file, plus the web service URL which can be found in the decompiled code. Thanks