[1] IEEE Paper: A SIP Security Testing Framework: Hemanth Srinivasan and Kamil Sarac.
[2] Applied Cryptography-Second Edition-Protocols, algorithms and Source code in C: Bruce Scheneier.
[3] SIP Tutorial: Daniel-Constantin Mierla.
[4] IEEE Paper: SIP Security Issues: The SIP Authentication Procedure and its Processing Load: Stefano Salsano, Luca Veltri, Donald Papalilo.
[5] IEEE Paper: Security Challenges for Peer-to-Peer SIP: Jan Seedorf.