Recent events in the US and elsewhere have given rise to renewed and more mainstream interest in cryptography. But while the more popular methods are slowly proving to be inadequate, a stronger option might soon be available in the form of DissidentX, a software made by Bram Cohen, more popular for having created the BitTorrent file sharing protocol.
It almost feels ironic that BitTorrent, which is probably more associated now with piracy and illegal activities, would have common roots with DissidentX, but the concept of peer-to-peer communication that bypasses the need for a central server, in a way, tries to keep things private between only the people involved. BitTorrent, the company, has even engaged in creating a more privacy-oriented cloud storage alternative called BitTorrent Sync.
The principle that DissidentX uses is actually based on an older and already existing cryptography method called stenography, which sounds almost straight out of a CSI or 24 episode. Stenography basically involves hiding the real content, be it text or an image, inside another, more unassuming content, like paragraphs or another image. The goal is to hide the message in plain view, hiding the fact that there is actually a hidden message embedded inside something inconspicuous.
Cohen's DissidentX software, however, tries to improve on this method in a number of ways. For one, instead of simply turning bits on or off to encode messages, Cohen opts to pass through the entire file through the cryptographic hash. This results in a cover text, or image that doesn't just have bits and pieces containing the encoded message. The encoded content and the cover are seamlessly mashed together into one. This makes it harder to detect that an image or text is actually a cover.
Another unique feature that Cohen is throwing in is the ability to encode multiple messages in a single cover. Each message will have its own decrption key independent of the others. This means that a single file can be used for different recipients, each receiving a different encoded message. What's more, DissidentX can also be used to disclose keys to fake content should the need arise, without the recipient knowing that the same file actually contains the valid content as well. This could be useful in case an activist or whistleblower gets apprehended and forced to cough out decryption keys. Those keys would then only disclose red herrings and keep the original message safe for its intended recipients only.
Bram Cohen has released the prototype for DissidentX over summer, but his work is far from over. For one, the software has still one glaring limitation, that the cover text is required to be exponentially larger than the hidden message itself. Cohen and a group of cryptography experts from Stanford University are currently at work in trying to whittle that requirement down to a more manageable size.