Let’s say that we want to communicate with someone secretly. We prefer that only the intended recipient have the ability to decode the contents of the communication. We obviously want to keep the message secret. Sounds familiar? A common solution to this problem is to use encryption. An encryption scheme takes a message and transforms it into an unreadable format so that an eavesdropper can’t read it. Now what if we don’t want anyone to find out that there is communication going on? As in, if the attackers don’t know that something is going on, then there are lesser chances of getting attacked right? How do we achieve this? Are there techniques to that allow us the hide this information?
Consider the earlier example. If we don’t want anyone to find out that there is something to be hacked, then we need to hide the fact that communication is taking place. This is where steganography comes into picture. Steganography differs from cryptography in the sense that cryptography focuses on keeping the contents of a message secret, where as steganography focuses on keeping the existence of a message secret.
As mentioned earlier, cryptography actually transforms the message that is being transmitted to make it obscure to anyone who may actually intercept the message. Unlike cryptography, steganographic techniques actually hide the message within another file, whether it is text, audio or image data. If the presence of hidden information is revealed or even suspected in steganography, then it’s purpose is partially defeated. Steganography doesn’t focus too much on obscuring the message itself. Steganography and cryptography are both ways to protect information from unwanted parties but neither technology alone is perfect and can be compromised. The strength of steganography can thus be increased by combining it with cryptography.
What is steganography exactly?
Let’s look at a few basic terms before we proceed. The modern formulation of steganography is often given in terms of the prisoner’s problem. In the prisoner’s problem, Alice and Bob are two inmates who want to communicate with each other in order to hatch an escape plan. The characters, Alice and Bob, are kind of famous in the realm of cryptography! So keeping up with the tradition, we will take our example forward using these characters. Anyway, coming back to the problem, all communication between them is examined by the warden, Catherine, who will punish them severely and put them in solitary confinement at the slightest suspicion of such secret communication.
In the general model for steganography, we have Alice wishing to send a secret message to Bob. In order to do so, she “embeds” the message into a cover-object, and obtains a stego-object. This stego-object looks like a regular object to an onlooker. This stego-object is then sent through the public channel. Going by this, we have the following definitions:
- Cover-object: Refers to the object being used as the carrier to embed messages into. Many different objects have been employed to embed messages into. For example, images, audio, and video as well as file structures, and html pages can be used.
- Stego-object: Refers to the object which is carrying a hidden message. So given a cover-object and a message, the goal of the steganographer is to produce a stego-object which would carry the message.
The actual formulation of steganography dives deep into the realm of information theory. Mathematical techniques and probabilistic frameworks are used to come up with optimal models for steganography. There is a lot of information available online. You can check out this article if you are interested.
Is steganography that useful?
The research in steganography has mainly been driven by a lack of strength in cryptographic systems. Crypto systems can be strengthened by using bigger keys, but the basic structure will still remain the same. You are just using a bigger lock! It’s basically still a lock and it just needs a bigger hammer to break it. Many governments have created laws to either limit the strength of a cryptographic systems, thus forcing people to study other methods for secure information transfer. Businesses have also started to realize the potential of steganography in communicating trade secrets or new product information. Avoiding communication through well-known channels greatly reduces the risk of information being leaked in transit.