Encrypt/ Secure Communication Android App <-> Rest Webservice

I want to create a backend for my android app with Tapestry5 and this http://code.google.com/p/t5-restful-webservices/ plugin. The app will communicate with the server by calling

Solution 1:

I can think of 2 approaches:

Use SSL to secure the connection. SSL can do a handshake checking the credentials. To authenticate the user you can use a certificate or a PSK.

Or you can simply create a Hash (SHA or MD5) of your data and include a key. This is called hmac. A reverse engineer may get the Key cause you have to hardcode it in your code.

Solution 2:

checking for the users UA could help...