In this paper, we evaluate available steganographic techniques for SIP
(Session Initiation Protocol) that can be used for creating covert channels
during signaling phase of VoIP (Voice over IP) call. Apart from characterizing
existing steganographic methods we provide new insights by introducing new
techniques. We also estimate amount of data that can be transferred in
signalling messages for typical IP telephony call.Comment: 8 pages, 4 figure