STEGANOGRAPHY

Steganography



Steganography

Introduction

Steganography (from the Greek for "covered writing") is the secret transmission of a message. It is distinct from encryption, because the goal of encryption is to make a message difficult to read while the goal of steganography is to make a message altogether invisible. A steganographic message may also be an encrypted as an extra barrier to interception, but need not be. Steganography has the advantage that even a talented code-cracker cannot decipher a message without knowing it is there.

Steganography: A Discussion

Por and Delina (2008) mention steganography has been used since ancient times; Greek historian Herodotus records how one plotter of a revolt communicated secretly with another by shaving a slave's head, writing on his scalp, letting his hair grow back, and sending the slave as an apparently unencumbered messenger. The number of ways in which a steganographic message might be sent is limited only by human ingenuity. A photograph of a large group of people, for example, might contain a Morse-code message in the expressions of the people in the photograph (e.g., smiling for dot, blank for dash) or in the directions they are looking (e.g., slightly to the left for dot, straight at the camera for dash). Writing in invisible ink or miniaturizing a message, as on microfilm, are also forms of steganography. Probably the commonest form of steganography involves the embedding of messages in apparently innocent texts, with the letters or words of the message indicated either by subtle graphic emphasis (e.g., heavier ink, lighter ink, a small defect) or by special positioning. For instance, reading the first word of every sentence in what appears to be an ordinary letter might yield a steganographic message (Por and Delina, 2008).

This may seem to be an ordinary beginning to an ordinary article. It is not. There's a secret message hidden here, in this very paragraph. It's not in view, and its source is modern. But the art of hiding messages is an ancient one, known as steganography.

Steganography is the dark cousin of cryptography, the use of codes. While cryptography provides privacy, steganography is intended to provide secrecy. Privacy is what you need when you use your credit card on the Internet -- you don't want your number revealed to the public. For this, you use cryptography, and send a coded pile of gibberish that only the web site can decipher. Though your code may be unbreakable, any hacker can look and see you've sent a message. For true secrecy, you don't want anyone to know you're sending a message at all.

Early steganography was messy. Before phones, before mail, before horses, messages were sent on foot. If you wanted to hide a message, you had two choices: have the messenger memorize it, or hide it on the messenger. In fact, the Chinese wrote messages on silk and encased them in balls of wax. The wax ball, "la wan," could then be hidden in the messenger (Por and Delina, 2008).

Herodotus, an entertaining but less than reliable Greek historian, reports a more ...