covert channels
Droplifting
Droplifting is the act of inserting one's own (often homemade) media into media distribution facilities (such as retail outlets).
The Anti-Shoplifting
Getting your ideas, your voice out there is hard sometimes, in the face of mainstream media super-powers. Droplifting provides an interesting method of introducing people to new media, because they simply stumble across it (often while they are operating in hard-core consumer mode).
Getting the Drop
Droplifting could be classified as a covert channel because a resource is being utilized in a way it was not (specifically speaking) designed to function in. It could also fall under the heading of Culture Jamming, as it is using corpolitical resources to spread alternative messages and memes.
Droplifting Examples
Banksy Punks Paris Hilton
Banksy Guantanamos Disneyland
Banksy Exhibits In Museums
—YouTube Video
Covert Channels
Covert Channels
A communications channel is simply a medium used to communicate. So, it follows that a Covert Channel is simply a channel hidden within some other medium.
Take the example of steganography. Steganography is the act of hiding information within a piece of media (such as an image or audio file). By injecting your message into a media file which goes out into the world to be downloaded (e.g. encoding a message into a photo, then uploading to flickr.com) you are using a covert channel.
When using a covert channel, it is important to take into account the idea of Security through Obscurity--namely, just because it's covert (no one knows to look there), doesn't mean it's invisible (i.e. it's still possible to discover the message, without knowing it was there in the first place).
This means you should also take care to protect your data (and yourself) in other ways (such as encrypting the message).
Covert channels are by nature, a parasitic form of communication (since they don't exist as a medium of their own, but instead use the bandwidth of some other service).
Some Types of Covert Channels
Steganography - Steganography itself is not a covert channel, but when used on a medium which can be distributed by some other channel, it becomes so.
Port Knocking - In this case, the covert channel used to convey information is the timing/order of communications requests to a particular series of network ports (e.g. you connect to say port 33, then 960, then 112, then 5442, in that order, and it acts as a key (telling the server listening on those ports to do something)--the code itself is the order which you hit the ports).
Protocol Hiding - Networking protocols carry a variety of info in addition to the contents of the packets being carried. By altering the data contained within these packets, info can be hidden within a network packet itself.
It is also important to note that the size (bandwidth) available depends heavily on the medium involved, and generally speaking, the more bandwidth being used, the more your message is likely to stick out like a sore thumb. Take for example, the above steganography case--each bit you encode into an image is altering the way that image is actually s'posed to look--if you change it too much, it will be obvious (to the naked eye) that something is wrong with the image.