Diogo Miguel Barrinha Barradas

Co-advisor: N. Santos

Unobservable Covert Streaming for Internet Censorship Circumvention

Tese submetida para provas de mestrado em Engenharia Informática e de Computadores Instituto Superior Técnico, Universidade de Lisboa.


Repressive regimes are known to deploy large-scale surveillance and censorship mechanisms in order to deter their citizens from accessing or publishing rightful information in the Internet. To evade the censors’ control over the access to information, recent systems enable the creation of covert channels by tunneling data through popular media streaming protocols. Unfortunately, the covert channel may induce patterns in the resulting packet stream that distinguish themselves from the packet patterns that characterize regular streams. If the differences are statistically significant, the censor may be able to un- veil, and subsequently block, the covert channel. Therefore, one of the main challenges in implementing this technique is to ensure that the covert channel remains unobservable from censors.

Considering this challenge, this thesis studies the encoding of arbitrary data on the video channel of widely used video-conferencing applications, such that the traffic characteristics of legitimate video- conferencing calls are preserved. Particularly, the thesis proposes and evaluates different alternatives to encode information within a video-stream, in order to maximize the available throughput while re- maining indistinguishable from legitimate video-conferencing traffic. A prototype of the system, named DeltaShaper, establishes a covert channel that offers a data-link interface and that can support any pro- tocol that runs over TCP/IP. The experimental evaluation's results show that it is possible to achieve a throughput of 0.4 KB/s while maintaining unobservability, which allows to run standard applications such as FTP, Telnet, or Wget.


Unobservable Covert Streaming for Internet Censorship Circumvention
Diogo Miguel Barrinha Barradas
MSc Thesis. Instituto Superior Técnico, Universidade de Lisboa.
September, 2016.
Available BibTeX, MSC Thesis, and extended abstract, and mid-term report.
Síntese de Vídeo para Evasão de Censura na Internet.
D. Barradas, L. Rodrigues e N. Santos
Actas do oitavo Simpósio de Informática (Inforum), Lisboa, Portugal, Sep. 2016.
DeltaShaper: Enabling Unobservable Censorship-resistant TCP Tunneling over Videoconferencing Streams.
D. Barradas, N. Santos, and L. Rodrigues.
In Proceedings of the 17th Privacy Enhancing Technologies Symposium, Minneapolis (MN), USA July 2017.

Luís Rodrigues