Date of Award


Degree Type


Degree Name

Doctor of Philosophy (PhD)


Electrical Engineering and Computer Science


Steve Chapin

Second Advisor

Carlos Caicedo


active warden, covert channel, IPv6, security

Subject Categories

Electrical and Computer Engineering


Every day the world grows more and more dependent on digital communication. Technologies like e-mail or the World Wide Web that not so long ago were considered experimental, have first become accepted and then indispensable tools of everyday life. New communication technologies built on top of the existing ones continuously race to provide newer and better functionality. Even established communication media like books, radio, or television have become digital in an effort to avoid extinction. In this torrent of digital communication a constant struggle takes place. On one hand, people, organizations, companies and countries attempt to control the ongoing communications and subject them to their policies and laws. On the other hand, there oftentimes is a need to ensure and protect the anonymity and privacy of the very same communications. Neither side in this struggle is necessarily noble or malicious. We can easily imagine that in presence of oppressive censorship two parties might have a legitimate reason to communicate covertly. And at the same time, the use of digital communications for business, military, and also criminal purposes gives equally compelling reasons for monitoring them thoroughly. Covert channels are communication mechanisms that were never intended nor designed to carry information. As such, they are often able to act ``below'' the notice of mechanisms designed to enforce security policies. Therefore, using covert channels it might be possible to establish a covert communication that escapes notice of the enforcement mechanism in place. Any covert channel present in digital communications offers a possibility of achieving a secret, and therefore unmonitored, communication. There have been numerous studies investigating possibilities of hiding information in digital images, audio streams, videos, etc. We turn our attention to the covert channels that exist in the digital networks themselves, that is in the digital communication protocols. Currently, one of the most ubiquitous protocols in deployment is the Internet Protocol version 4 (IPv4). Its universal presence and range make it an ideal candidate for covert channel investigation. However, IPv4 is approaching the end of its dominance as its address space nears exhaustion. This imminent exhaustion of IPv4 address space will soon force a mass migration towards Internet Protocol version 6 (IPv6) expressly designed as its successor. While the protocol itself is already over a decade old, its adoption is still in its infancy. The low acceptance of IPv6 results in an insufficient understanding of its security properties. We investigated the protocols forming the foundation of the next generation Internet, Internet Protocol version 6 (IPv6) and Internet Control Message Protocol (ICMPv6) and found numerous covert channels. In order to properly assess their capabilities and performance, we built cctool, a comprehensive covert channel tool. Finally, we considered countermeasures capable of defeating discovered covert channels. For this purpose we extended the previously existing notions of active wardens to equip them with the knowledge of the surrounding network and allow them to more effectively fulfill their role.


Open Access