Invisible Ink to Pixels

Posted July 08, 2010, at 7:55 p.m.

In the spy world, the case of the suspected Russian spies shows some old-fashioned tricks still prove to be the best way to communicate, although new ones are making inroads.

TechNewsDaily, “a new source of technological news for non-geeks,” lists five old communication systems that the alleged spies arrested by the FBI were using.

First is invisible ink, in use since World War I and, if you can believe it, the recipe is still classified as secret. What looks like a blank sheet of paper — or maybe some misleading printed material — contains invisible material that can be restored by someone at the other end who knows how.

Shortwave radio, also used by the Russian spy suspects, has been an espionage favorite since the 1950s, but the transmitters now employ digital chips instead of the old vacuum tubes.

Burst transmissions can rush a radio emission so fast that it is impossible to recognize it as human speech and hard to fix its point of origin before the message is all gone.

Numbered sequences, groups of numbers that can be unscrambled by the recipients, were used by the British in World War II to alert the French Resistance that an invasion was coming or to assign specific sabotage targets.

Transposition ciphers, developed in World War II and still protected by secrecy classification, use spinning disks to scramble and unscramble text.

TechNewsDaily quotes Mark Stout, the historian at the International Spy Museum in Washington, D.C., as saying, “Newer is not always better. High tech may be better than low tech in some situations, but in others it may be grossly inappropriate.”

One new technique, only rumored until the alleged Russian spies were charged, involves secretly encoding messages in ordinary photographs on publicly available websites. Details of what the supposed Russian agents embedded in the pictures and how they did it are still secret.

As Steven Bellovin, a computer science professor at Columbia University, explains it, a computer generates a picture on its screen by assigning every pixel three numeral values for the amounts of red, green and blue in the display. By slightly changing the numbers, a spy can hide the 1’s and 0’s of computer language in a picture’s pixel numbers while the picture looks the same to the human eye.

Professor Bellovin calls the system a modern form of “steganography,” or concealing messages within images, so that instead of just encrypting a message, the sender can conceal even the fact that any message has been sent. The FBI showed a photo of the Washington Monument that it said contained in its data a map of an American airport.

Just what Moscow has been getting out of all this remains a mystery, but the glimpse into “spy technology” — old and new — is fascinating.

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