Encrypted VoIP communication using the integrated Android 2.3 SIP stack

I'm currently working on a project where I have to implement a secure VoIP communication between Android 2.3 (or higher) phones. The connection is established through a Kamailio server.

The requirement is that the SIP API provided by Android (since version 2.3) is used (if possible).

I think the biggest problem is that the connection is made from classes in the android.net.rtp p开发者_StackOverflow中文版ackage. But all these classes don't belong to the public API, therefore I cannot extend these classes and make my own changes to them.

Now my question: Is it still somehow possible to establish an encrypted connection by using SRTP (or ZRTP for that matter)? And if so, how should I approach that?

If it is not possible to do with the SIP API from Android, what would be a good alternative to do so?

Thank you in advance!

android.net.rtp is public as of Android 3.1. If you are developing for 3.1 or later then you can extend from these, otherwise you'll need to implement your own.

Aha! Android 3.1 just released. These classes are now marked as available since API level 12