An Exploration of covert channels within voice over IP

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Title: An Exploration of covert channels within voice over IP
Author: Lloyd, Patrick
Abstract: In the following thesis, an overview of covert channels within Voice over IP is given and then expanded upon by presenting an experiment which proves the ability to hide messages within the Session Initiation Protocol (SIP) and Session Description Protocol (SDP) of a Voice over IP packet. The plain text nature of the SIP and SDP packets allow for an easily embedded message to be encoded into the expected data, while also being "hidden in plain sight" due to the packet only being sent once per VoIP session. While previous papers [15] have proposed the ability to hide covert messages within the plain text SIP and SDP packets of a VoIP call stream, this thesis is the first to carefully analyze and test the ability to embed data in these packets and send a covert message, based on an agreement between the sending and receiving parties. Results include the success for covert messages to be hidden within the Max-Forwards field, a field used for the total number of hops between sender and receiver, the V field, a field used for the version of SIP being used, the T field, usually used for the time a session becomes active on the sending and receiving ends, and finally the O field which designates the owner the call was originally sent from. This success was met with equal failure of previously proposed abilities to hide messages [15] in the Branch statement, tag field, and Call-ID field. A method for systems administrators or network administrators to detect covert channels coming in over a VoIP enabled network using a simple, modified java based packet capture tool is then presented with the ability to check the Max-Forwards, V, T and O fields, due to their low entropy and easy detectability. Using this method, a discussion is given regarding the detectability of covert channels as compared to previous research papers.
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Date: 2010

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