The Code Within

Ancient Greeks devised a unique way to get past the opposition army surveillance. The persons manning the army check post would search them thoroughly, to intercept and retrieve any possible information they might be ferrying across. Yet, despite all these, messages did get across. How did the Greeks do it?

They shaved the heads of the messengers, then they tattooed the messages on their tonsured heads, and waited till new hair-growths covered the messages etched on the scalp. The non-suspecting gatekeepers would let them through. On the other side, people would only have to shave their heads to get the real missive. Sounds like the modem (modulator demodulator)? Not quite!

Steganography is the science and art of foisting texts or pictures in this fashion. Supposing that we draw a black and white picture, then we superimpose on it, some text in yellow color. It won't make much difference to the human eye, as our sensitivity to the yellow color is very minimal. You can see for it yourself. But a camera, or even the one in your phone, will pick it up faithfully. It can then transmit (via Bluetooth or infrared or any compatible device) this modified picture to another phone or the internet; which can decipher the information contained therein.

I came across an article in the PC Quest magazine, August 1994 issue. It was called Visions in Noise. It was about a similar topic, called random dot stereography. The picture ( looked more like an ultrasound scan!) was astounding. When the focus was right, four 3D spheres would emerge out of the blue.

These cryptographic techniques and their cousins could be employed in identification protocols (like Radio Frequency ID), espionage, in behavioral studies of primates (as in inkblot test) or in advertising campaigns, in computer softwares, financial transactions over the net etc.