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!

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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.

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