5. SIP security

The security situation in a SIP system is similar to that encountered in H.323 architectures. The requirements are the same, covering aspects such as user and system authentication, message confidentiality (both for signaling and multimedia flows) and message integrity.

The various SIP messages can be encrypted to prevent them from being read by a malicious user, and to prevent the latter from perceiving the communication "pattern" (who is calling whom and how). Three types of encryption are available:

• end-to-end encryption of the message body and certain headers (only the sender and recipient know the content);

• close-to-close encryption (server-to-server), at network or transport level, using either IPSEC (IP Security) or TLS (Transport Layer Security), like H.235 to prevent eavesdropping...