Steganography

Introduction

History

'A picture paints a thousand words, with Steganography a picture encodes a thousand words.'

Steganography is the art or science of encoding a message within something else. Steganography is involved with the hiding of a message in generally something that can be observed to carry its own message as well.

Steganography has been used for centuries, and is in fact a word of Greek origin, meaning covered or hidden writing.

Steganography was used in Ancient times and its origins can be traced back to 440 BC. Herodotus of Halicarnassus, a Dorian Greek writes in the The Histories, an account of the Greco-Persian Wars, about the use of Steganography.

Two examples of early Steganogpraphy are given, one involves the writing of a message on a tablet, covering the tablet in wax and then writing another message on the top. As wax was often used to cover tablets to allow reuse of the tablet, the actual message remained hidden. The other example was the shaving of the head of a slave by Histiaeus, the tattooing of the message upon the shaven head and then allowing the hair to be regrown.

Lemon juice, paper and heat.
Microdot.
Paper wound around a rod of a certain diameter (scytale).
Mad's paper folding technique.
Newspaper columns, especially obituries and personal ads.
Pin pricking holes above the letters in newspapers.
Chinese technique of silk writing, waxing, swallowing and retrieval.
Prearranged signaling of any type, that would otherwise appear to be normal communication or behaviour.

Steganography and Encryption

Steganography is not encryption, though of course they are linked. Steganography comes closer to the security by obfuscation side as opposed to security by mathematically hard to reverse encryption techniques.

Steganography attempts to hide the existance of a message. Encryption accepts the message may be found, though it will be hard to decipher unless the key is known, or a brute force attack of trying many key combinations is used.

Combining Steganography and encryption is a very powerful security technique, the chance of your message being found is low, even lower if the message does not look like a message when found, and if found it then also has to decrypted. Weaving the use of encryption and Steganography at different stages of the process of message creation and message transmit will further frustrate message interception, detection and deciphering.

Digital Steganography

We now live in the information age, more precisely we now live in the age of digital information. Digital information is peculiar to analog information in that there is a definite state to represent any data that comprises information. Data is raw, and generally a computer system is a two state machine, it is either on or off, 1 or 0 (multi state machines do exist but this two state model has proved very useful). Data is stored in either a 1 or 0 state, by combining data and context we get information.

It is the context and the abstraction layers around the information that digital Steganography utilises. The data of the original message is encoded in 1s or 0s but it is part of a cover message, that will generally be made up of more data than the actual message. So, the cover message is important.

Most information flows over the internet, this traffic nowadays is in the form of TCP/IP communications, files play a large part in this communication as well. Files of a raw text nature perhaps offer us less of a chance to create a Steganography message, though still possible. The best candidates for Steganography cover message are image and sound files. Fidelity plays an important part in translating sound and imagery to digital format and that fidelity offers an excellent place for the hidden message.

Image and sound files are ubiquitous on the internet mainly because of the web, and its multimedia approach to information presentation. Image and sound files are also transmitted on other protocols than just http and https, ftp, and other application specific protocols are also used to transmit them. People also store photography and sound for their own pleasure, personal photography is very common perhaps more so than personal sound generation. It is in this mix of interpretative data that digital Steganography can exist.

Steganography Terms

It is useful to be aware of some of the terms commonly used in Steganography and encryption.

Steganography and Encryption Terminology
Term	Meaning
Copyright Poised Solutions Ltd
ClearInfo	Message immediately comprehensible to a human.
PlainInfo	The real message to be sent.
CoverData	Data to be used to hide the plainInfo in.
CoverInfo	Information to be used to hide the plainInfo in.
StegData	CoverData and plainInfo merged using Steganography.
StegInfo	CoverData and plainInfo merged using Steganography, representation is still comprehensible.
CompressedData	Compressed data.
CompressedInfo	Compressed information.
CipherData	Encrypted information or data.
StegpherData	CoverData and cipherData merged using Steganography.
StegpherInfo	CoverData and cipherData merged using Steganography, representation is still comprehensible.
Key	Value of an equation used to lock or unlock cipherData.
CipherInfo	Encrypted information when the key and algorithm of CipherData is known.

You may often see the word text used instead of data or info, this is historic in reason as most message would be passed in text. I have camel cased the Data in the word possibly to annoy camelCase detractors, though really this is done to add a diferent dimension to Steganography as it pertains to the digital world. Info is a contraction of the word information, and information is data plus context. I leave it as an exercise for the reader to go between the lines, and create their own reasons.

Previous page - Home

Steganography Home

Next page - Explanation

Further References