SkyDe (Skype Hide)...

SkyDe (Skype Hide): the press releases including the link to the full paper !


Our research on information hiding in Skype called SkyDe (Skype Hide) was described in New Scientist by Paul Marks - Silent Skype calls can hide secret messages (05.01.2013). Press releases were also included in The Economist - Speaking with silence and in IEEE Spectrum by Samuel K. Moore - SkyDe Software Sends Hidden Messages in Skype Calls.

See Press section for other media releases [link].


The paper by W. Mazurczyk, M. Karaś and K. Szczypiorski entitled "SkyDe: a Skype-based Steganographic Method" has been published in:

International Journal of Computers, Communications & Control (IJCCC), ISSN: 1841- 9836, 8(3), June 2013, pp. 389-400

The paper is available here: [link]


Read authors' bios: [link]

Steganography is an information-smuggling technique—the communication of secret messages inside a perfectly innocent carrier. One kind is the network steganography that to perform hidden communication, utilizes network traffic as the carrier for secret data. Steganographic methods are aimed at hiding of the very existence of the communication, therefore any third-party observers should remain unaware of the presence of the steganographic exchange.

After the 11 September attacks in 2001, rumors flew that they had been carried out with some help from steganography. A 2001 New York Times article described fake eBay listings in which routinely altered pictures of a sewing machine contained malevolent cargo. The link to 9/11 was never proved or disproved, but after those reports, the interest in steganographic techniques and their detection greatly increased.

In 2002 at Warsaw University of Technology, Poland the special project ( was founded by Prof. Krzysztof Szczypiorski that has been focused on network steganography. For more than a decade our efforts provide innovations in data hiding for existing networks including wireless LANs, IP telephony and Internet.

Steganography use is on the rise, and not just among criminals, hackers, child pornographers, and terrorists. Persecuted citizens and dissidents under authoritarian regimes use it to evade government censorship, and journalists can use it to conceal sources etc.

You can also read more about steganography at this [link].

Skype is so called proprietary service that design details are not publicly available. However, many researchers tried so called reverse engineering to understand how it works. Also many researchers monitored and analyzed Skype traffic to see how its protocols really operates. We were analyzing the measurement studies on Skype traffic as well as we conducted them ourselves. This way we discovered that Skype traffic can be used for information hiding i.e. based on this knowledge SkyDe was designed and implemented.

When you say something Skype “produces” larger packets (e.g. 130 bytes) and when you are saying nothing at all they are smaller (e.g. 70 bytes). Both types of packets are encrypted. SkyDe takes advantage of this relationship. When you can identify that there is silence in Skype call by finding the smaller packets, you can replace their content with the secret data. Thus, SkyDe just erases encrypted silence from Skype data packets and it replaces it with encrypted secret data. This makes it also very hard to detect!

Based on our experimental results it turned out that the transmission up to 3 kbps can be achieved. This is not sufficient for audio/video transmission in real-time, however audio/video files can be transferred to the other side without problems as well as text documents.

Of course SkyDe can be utilized by decent users who use their own Skype calls to exchange covert data, but also by intruders who are able to covertly send data using third party calls (e.g. in effect of earlier successful attacks by using trojans or worms etc.). This is a usual tradeoff: every invention can be used with good or bad intentions. For example, you can use knife to cut a loaf of bread or to stab someone...

The video describing the details of SkyDe can be found below:

Visit later for more information on SkyDe!