uld also be secured. Unlike traditional mobile phone text messages which are protected by the network and therefore are forced to remain unmodified from sender to des- tination, SIP text messages can be modified in transit because they are not secured. SIP messages may contain information a user or server wishes to keep pri- vate. The headers can reveal information about the communication patterns and content of individuals, or other confidential information. The SIP mes- sage body may also contain user information (media type, codec, address and ports, etc) that should not be revealed. 22.3.1.1 Messages not Encrypted Traditionally SIP messages are not encrypted and are therefore open to inter- ception in the links or at any points in the network. The 'To' and 'Via' fields of the headers are visible SO that SIP messages can be routed normally. This makes it possible for an attacker to send spoofed INITIATE messages with deceitful IP addresses. Furthermore, it is possible to use a spoofed BYE mes- sage to end SIP sessions prematurely. While this might require capturing SIP messages and holding them for use, it is not a hard task. There are several methods that can therefore be used to protect SIP mes- sages. They include using security mechanisms such as IPSec, TLS/SSL and S/MIME. Another approach is to deploy firewalls at the perimeter of the network to protect and provide application layer security as well as authenti- cation. This also protects against transport layer and protocol attacks. Secur- ing SIP header and overall information can be implemented for the following reasons: 1. Maintaining private user and network information in order to guarantee some form of user privacy. 2. Avoiding SIP sessions being established or charged by someone faking the identity of another person. 22.3.2 Threats in SIP Communication Chain Threats exist at all levels of SIP operations, at the servers, proxies, the SIP addresses, messages and requests and the message headers: © 2009 by Taylor & Francis Group, LLC SIP Security and