amazon style, read http://www.thebuzzmedia.com/designing-a-secure-rest-api-without-oauth-authentication/
for client side , see Google I/O 2010 http://www.google.com/events/io/2010/sessions/developing-RESTful-android-apps.html

What I have done so far, consume RESTful web service from server side, without any authentication.
So, my next step is to implement authentication like AMAZON.

I use OpenSSL to create the key pair, it is in pem format (text).
Then, I am stuck, I need to store the private key in my android app or file system (SD), then retrieve it, encrypt my request with it and send it out.

My questions are, how do I store it? use KeyStore? I search for it and people load it from JKS/DER file, Android use BKS, so, do I need to generate a BKS using openSSL? or is there a way to store pem format string into KeyStore?
after that, how to use my KeyStore to encrypt String/Text? like KeyStore.GetEncryptStream()?

Please shed some light on this, thank you.