RTP: Audio and Video for the Internet

Various privacy issues are inherent in the use of RTCP ”in particular, source description packets. Although these packets are optional, their use can expose significant personal details, so applications should not send SDES information without first informing the user that the information is being made available.

The use of SDES CNAME packets is an exception because these packets are mandatory. The inclusion of an IP address within CNAME packets is a potential issue. However, the same information is available from the IP header of the packet. If the RTP packets pass through Network Address Translation (NAT), the translation of the address in the IP header that is performed should also be performed on the address in the CNAME. In practice, many NAT implementations are unaware of RTP, so there is a potential for leakage of the internal IP address.

The exposure of user names may be a greater concern ”in which case applications may omit or rewrite the user name , provided that this is done consistently among the set of applications using CNAME for association.

Some receivers may not want their presence to be visible. It is acceptable if those receivers do not send RTCP at all, although doing so prevents senders from using the reception quality information to adapt their transmission to match the receivers.

To achieve confidentiality of the media stream, RTCP packets may be encrypted. When encrypted, each compound packet contains an additional 32-bit random prefix, as illustrated in Figure 5.12, to help avoid plain-text attacks.

Security and privacy are discussed in more detail in Chapter 13, Security Considerations.