GSM Security

Hello Friends,
I need to do an assignment on GSM Security. I need from you people. Which security techniques are used in GSM security, the cryptography, algorithm, keys, about all this.
Please if you people have any papers, document, or web link so share it with me.

Thanks

See this PDF .
And look here " http://www.gsm-security.net/gsm-security-papers.shtml "