YouSkyde: Information Hiding for Skype Video Traffic

📝 Abstract

In this paper a new information hiding method for Skype videoconference calls - YouSkyde - is introduced. A Skype traffic analysis revealed that introducing intentional losses into the Skype video traffic stream to provide the means for clandestine communication is the most favourable solution. A YouSkyde proof-of-concept implementation was carried out and its experimental evaluation is presented. The results obtained prove that the proposed method is feasible and offer a steganographic bandwidth as high as 0.93 kbps, while introducing negligible distortions into transmission quality and providing high undetectability.

💡 Analysis

In this paper a new information hiding method for Skype videoconference calls - YouSkyde - is introduced. A Skype traffic analysis revealed that introducing intentional losses into the Skype video traffic stream to provide the means for clandestine communication is the most favourable solution. A YouSkyde proof-of-concept implementation was carried out and its experimental evaluation is presented. The results obtained prove that the proposed method is feasible and offer a steganographic bandwidth as high as 0.93 kbps, while introducing negligible distortions into transmission quality and providing high undetectability.

📄 Content

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YouSkyde: Information Hiding for Skype Video Traffic

Wojciech Mazurczyk, Maciej Karaś, Krzysztof Szczypiorski, Artur Janicki Warsaw University of Technology, Institute of Telecommunications
Warsaw, Poland, 00-665, Nowowiejska 15/19

Abstract. In this paper a new information hiding method for Skype videoconference calls – YouSkyde – is introduced. A Skype traffic analysis revealed that introducing intentional losses into the Skype video traffic stream to provide the means for clandestine communication is the most favourable solution. A YouSkyde proof-of-concept implementation was carried out and its experimental evaluation is presented. The results obtained prove that the proposed method is feasible and offer a steganographic bandwidth as high as 0.93 kbps, while introducing negligible distortions into transmission quality and providing high undetectability.

Key words: information hiding, Skype, network steganography

Introduction The last few years have been marked by the proliferation of various multimedia services for Internet protocol (IP) networks: IP telephony, videoconferencing, Video on Demand (VoD), online games, IP-TV and so on, and this has significantly changed the way we communicate, work and entertain. From the network traffic perspective, these services typically exchange data in the form of streams, and the resulting traffic is characterized by quite a high volume of up to hundreds of packets per second. Also, not uncommonly the generated data is transmitted in an encrypted form. One of the most popular services of this kind is Skype, which not only allows IP telephony or videoconference calls to be conducted, but also chat messages to be exchanged and/or the sharing of files. Skype is a proprietary peer-to-peer (P2P) telephony service originally introduced in 2003 by the creators of the famous P2P file-sharing system, Kazaa (Niklas Zennström and Janus Friis). Currently, it is owned by Microsoft and in 2013 it was used by more than 280 million people every month [12]. In June 2014, the highest number of simultaneous users online was reported (about 80 million [11]), and recently Skype’s share of the world’s international telephone market has exceeded 40% [10]. A variety of information hiding methods has been used throughout the ages by people. One of these methods is steganography, the main aim of which is to embed a secret message into a carefully selected carrier [17]. The youngest branch of this information hiding subfield is network steganography. To perform hidden communication, it utilizes network protocols and/or their relationships as the hidden data carrier. Network steganography is typically utilized to create a covert network channel; thus, it is intended to hide the very existence of the communication. Thus, any third-party observer would remain unaware of the presence of the steganographic exchange. This particular feature of network steganography makes it suitable for applications where stealth is of crucial importance [18]. We believe that the most important use of network steganography is to provide a means of clandestine communication to improve the user’s privacy. Hence, information hiding techniques can be used as part of the tool, for example, to fight censorship in oppressive regimes. Skype is unquestionably well-fitted for covert communication purposes, mainly because of its popularity and traffic volume, and because, as mentioned earlier, any steganographic method requires a well-selected hidden data carrier to succeed. An ideal candidate for a carrier should: (i) be popular, in other words, usage of such a carrier should not be considered an anomaly in itself – the more such carriers are present and utilized on the network the better, because they mask the existence of hidden communication; (ii) the modification of the carrier related to the embedding of the steganogram should not be “visible” to the third party, who is unaware of the steganographic procedure. Thus, targeting Skype was a natural choice for steganographers as it fulfils both of these requirements. In general, every network steganographic method can be described by the following set of characteristics [2]:
 Steganographic bandwidth, which refers to the amount of secret data that can be sent per unit of time when using a particular information hiding technique;  Undetectability, which is defined as the inability to detect secret data within a certain carrier; 2

 Robustness, which is defined as the amount of alteration that secret data can withstand without being destroyed.  Steganographic cost, which indicates the distortion of the hidden data carrier caused by applying the steganographic method.

It must be emphasized that a good steganographic method should be as robust and as difficult to detect as possible, whilst offering the highest bandwidth. However, it should be noted that a fundamental trade-off is always necess

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