Image by Arnold Straub
Steganography is the practice of concealing a message within another message or a physical object. In computing/electronic contexts, a computer file, message, image, or video is concealed within another file, message, image, or video.
Where cryptography is the art of concealing messages from prying eyes, steganography tries to hide the fact that a message was sent at all.
Imagine intercepting a letter with one line, "uryyb jbeyq". One would be astute to suspect that some form of encryption was involved. Indeed, "uryyb jbeyq" is an encryption of "hello world" under ROT13.
Imagine now, intercepting another letter with one line, "hello world". Perfectly literate content, albeit somewhat nonsensical. Even the most suspecting observer, however, might never have guessed that in all that blank space sat an entire message written in invisible ink.
That is the power of steganography - there is nothing to intercept if one does not even register the possibility of a hidden message. Steganography in general, and in digital steganography especially, attempts to hide one thing in another by means of camouflage, in ways similar to how a chameleon blends into its surroundings.
For more information on steganography, watch this.
Chameleon is a collection of MATLAB scripts and functions that perform steganographic operations. These tools allow users to embed and recover all kinds of binary files in and from photographic images. For a video demo, click here.
- Document files (Word, Excel, PDF, etc...)
- Media files (JPG, MP3, MP4, etc...)
- Source codes (C, Python, Rust, etc...)
- Small programs or executables
- Any byte-representable computer file
Why would anyone need something like that? Glad you asked!
One reasonable motivation is being able to feel like a hacker. Hide you school homework, grandfather's address or text files containing secret keys inside an image of a cute puppy and send it to your friends! Have them clone this git repository and - viola! - you have your own secret communication channel!
Need to hide a secret? Well, you can!
For a video demo on how to use Chameleon, click here.
Currently these modes of operations have been implemented/ are planned:
- LSB Encode
- LSB Decode
- DCT Encode (pending...)
- DCT Decode (pending...)
Chameleon embeds binaries in a lightweight manner. A 64-bit integer
num_bytes denotes the size of the original binary embedded. Within the
modified image, the LSBs of the first 64 pixels form the
serialized
num_bytes exactly. The LSBs of the next num_bytes * 8 pixels form the
serialized
binary exactly.
To retrieve a piece of binary from an image that was steganographically modified, one needs to know how the binary file was embedded in the first place. That varies from implementation to implementation.
This necessarily implies that Chameleon can only extract binaries from images that (i) contain binaries embedded by Chameleon itself or; (ii) contain binaries that were embedded in exactly the same way as Chameleon would have embedded it (very unlikely).
Currently, binary files can only be embedded in images that are at least 8x larger. To be safe, ensure that images are at least 10x larger.
Here, the size of an image refers to the product of its dimensions in pixels multiplied by the number of color channels available. An RGB image (so 3 channels) with dimensions 100px by 200px will have a size of 100 * 200 * 3 = 60,000 bytes.
I have no intention of re-developing Chameleon in another (more popular) programming language. Unfortunately, I am a student and have no time to do that.