Cryptography vs. Steganography

Cryptography is the practice of ‘scrambling’ messages so that even if detected, they are very difficult to decipher. The purpose of Steganography is to conceal the message such that the very existence of the hidden is ‘camouflaged’. However, the two techniques are not mutually exclusive.

Steganography and Cryptography are in fact complementary techniques. No matter how strong algorithm, if an encrypted message is discovered, it will be subject to cryptanalysis. Likewise, no matter how well concealed a message is, it is always possible that it will be discovered. By combining Steganography with Cryptography we can conceal the existence of an encrypted message. In doing this, we make it far less likely that an encrypted message will be found. Also, if a message concealed through Steganography is discovered, the discoverer is still faced with the formidable task of deciphering it.

Introduction to Steganography

Steganography is the art of concealing the presence of information within an innocuous container. Steganography has been used throughout history to protect important information from being discovered by enemies. A very early example of Steganography comes from the story of Demartus of Greece. He wished to inform Sparta that Xerces the King of Persia was planning to invade. In ancient Greece wax covered wooden tablets were used to record written text. In order to avoid detection by the Persians, Demartus scraped the wax from a tablet, etched the message into the underlying wood, then recovered the tabled with wax. This concealed the underlying message from the sentries who inspected the tablets as they left Persia by courier for Greece.

Another historical exampls of Steganography are the use of invisible inks. A common experiment conducted by young kids everywhere is to use a toothpick dipped in vinegar to write a message on a piece of paper. Once the vinegar dries, the presence of the message is not obvious to a casual inspector (aside from the smell). Upon slight heating of the paper, a chemical reaction occurs which darkens the vinegar and makes the message readable. Other, less smelly, invisible inks have been used throughout history similarly even up until World War II.

A more recently developed Steganography technique was invented by the Germans in World War II, the use of microdots. Microdots were very small photographs, the size of a printed period, which contain very clear text when magnified. These microdots contained important information about German war plans and were placed in completely unrelated letters as periods.

Although Steganography is related to Cryptography, the two are fundamentally different.