Security is more socially critical in multimedia communication than in traditional data communication. Intrusion or disclosure of human-human communication is more keenly felt than of ``mere'' data.
Unicast and multicast multimedia communication require some additional techniques for protection against these and a variety of other security attacks. For example, there is a temptation to believe that multicast is inherently less private than unicast communication since the traffic visits so many more places in the network. In fact, this is not the case except with broadcast and prune type multicast routing protocols dvmrp . However, IP multicast does make it simple for a host to anonymously join a multicast group and receive traffic destined to that group without the other senders and receivers knowledge. If the application requirement is to communicate between some set of users, then strict privacy can only be enforced in any case through adequate end-to-end encryption.
RTP specifies a standard way to encrypt RTP and RTCP packets using private key encryption schemes such as DES [#!des!#]. It also specifies a standard mechanism to manipulate plain text keys using MD5[#!md5!#] so that the resulting bit string can be used as a DES key. This allows simple out-of-band mechanisms such as privacy-enhanced mail to be used for encryption key exchange.