Party Algorithm Hides Messages in Ibiza Trance Music

The idea of using music to send messages has a long and veritable history. The German Benedictine monk Johannes Trithemius is widely credited with founding the discipline in the 16^th century. And various others have run with the idea, with techniques such as mapping notes to letters (developed by the 17^th century German priest Gaspar Schott). More recently, cryptographers have developed a wide range of electronic techniques for hiding messages in digital music.

So it’s easy to imagine that the options have been exhausted as far as developing new forms of musical steganography.

Not so. Today, Krzysztof Szczypiorski at the Warsaw University of Technology in Poland reveals an entirely new form of musical steganography which he developed specifically for electronic Ibiza club music. The new method exploits the trance-like rhythms that this kind of music is famous for.

Ibiza is one of several Balearic islands that sit some 100 miles off the coast of Spain in the Mediterranean Sea. It is famous partly for its beautiful towns and villages but mainly for its nightlife and the electronic music that has evolved in the clubs and in beach raves on the island.  It is electronic music that is characterised by a strong trance-like beat that encourages dancing – a beat that moves the feet!

Szczypiorski’s technique is to vary the tempo of the beat in a way that encodes information. But any changes have to be too subtle for human listeners to notice.

This kind of audio modification is possible because of modern digital audio workstations which allow various elements of compositions to be manipulated. For example, DJs often alter the tempo of music to mix it together, a particular feature of the Ibiza music scene.

Szczypiorski began by developing a simple Morse-like code in which he could spell out a series of dots and dashes to send messages. To indicate a dash, he speeds up the tempo for a single beat and to indicate a dot, he slows it down.

He used Appel’s Logic X pro digital audio workstation to create a range of covers of popular songs without lyrics. These included Miracle by Queen at 92 beats per minute, So What by Miles Davies at 120 beats per minute and Rhythm is a Dancer by Snap! at 130 beats per minute. “All original covers were prepared without any vocal parts and arranged in techno, hip-hop, or trance styles with the instruments available in Logic X Pro,” he says.

He then varied the temp in a way that encoded the message “Steganography is a dancer!”, which in Morse code looks like this;

…  –  .  –.  .-  -.  —  –.  .-.  .-  .–.  ….  -.–

..  …  .-  -..  .-  -.  -.-.  .  .-.  -.-.—

The message appeared twice at random in each piece of music.

A key question is to determine by how much to change the tempo so that the message is hidden from human listeners. To find out, he asked 20 people to listen to the music at an open air summer party. Ten of these people had backgrounds as musicians.

The results show that the method is clearly viable. When Szczypiorski changed the tempo by more than 3 per cent, about half the listeners noticed the difference. But when the change was less than 2 per cent, nobody noticed.  “At this level the experiment was stopped, because the rest of the party did not care about the music,” he says.

He goes on to suggest that it would be a simple matter to develop software that automatically encoded or decoded messages sent this way.  Szczypiorski calls it StegIbiza.

Of course, it’s unlikely that the world’s cyberspies will converge on the danceclubs of Ibiza to send hidden messages to one another. A much more likely scenario is that musicians might use StegIbiza to send messages to fans in the know. Or the method could be used to embed meta-information about the music into a recording which can then be read by music algorithms.

Either way, Szczypiorski has clearly had some fun coming up with and testing his idea. Trithemius would surely approve.

Ref:  arxiv.org/abs/1608.02988 : StegIbiza: New Method for Information Hiding in Club Music