Chapter 14. Securing Multimedia Communications

Information transfers over the open Internet are subject to all kinds of security threats; multimedia communications are no exception. Securing multimedia communications includes two aspects: securing the signaling plane (i.e., SIP), and securing the media plane (e.g., RTP, MSRP, TCP, and so on). Security in SIP signaling is decoupled from security in the media plane; for example, any media associated to a session can be encrypted end to end independently of any SIP signaling. In this chapter, we will review the fundamental approaches for securing each of the planes.

Security in SIP is a topic that deserves particular attention. There are several aspects in SIP that make it a difficult protocol to secure—for instance, its use of intermediaries or its expected usage between elements with no trust at all. For that reason, there is not a single mechanism that solves all the issues. Rather, SIP uses a combination of different security mechanisms depending on the scenario. Furthermore, most of these mechanisms already exist in other remits of the Internet, and are just reused or adapted to secure SIP.