University of Rochester

A Cloaking Device for Top-Secret Faxes

September 22, 1995

University of Rochester engineers have invented a way to secure fax transmissions from the prying eyes of co-workers, the boss, competitors, or fax handlers at public outlets such as convenience stores and hotels.

The software would be valuable to anyone seeking more privacy: an election year operative transmitting secret campaign strategy, a busy executive awaiting the day's sales figures at the hotel, or a worker swapping notes or jokes with a friend across town. The method could even be used as part of a children's toy or even an advertising scheme, say the inventors.

All faxes incorporating the Rochester encryption method look the same to the naked eye: a random pattern of black and white dots, like a white page filled with tiny black worms. No text is visible. Hidden within the pattern is the message, which can only be read by placing a special customized plastic sheet over the coded fax.

"There are many ways to encode and decode data, but I've never seen a hand-held optical device like this for coding messages," says graduate student Meng Yao, who developed the software with Kevin Parker, professor of electrical engineering.

"The key is in the way the printer lays down the squiggles," says Yao. "There are an almost infinite number of ways to encode the data, so every user can have a custom encryption key." A machine could be equipped with any number of codes suited to different executives who would each carry his or her custom decoding sheet.

Only when the decryption key is placed over and aligned with the fax is it readable. The text appears either as white lettering against a black background, or as dark lettering against a white background.

The technology could be part of a computer fax package, or it could be included in the internal brain of a standard fax machine. The user's custom plastic key can decode any fax sent by a machine equipped with the program; the software is not necessary for a receiving machine. "All fax machines do a digital handshake at the beginning," says Parker, "and that's all that our software requires." The encoding technology does not slow the scanning or transmission of the fax.

Parker and Yao are currently seeking a company to license and develop the technology. Parker estimates the cost of the software incorporated into a fax machine would be minimal, perhaps the cost of fax software programs now available.

Parker and Yao are currently working on refining the technology. For instance, because resolution varies among fax machines, it's not always easy to decode the text. And oftentimes characters must be at least one-third of an inch high to be legible; any smaller and the letters are drowned out by the worming pattern. Yao and Parker believe these problems will be solved as fax machines have finer and finer resolution and are connected to devices such as laser printers.

The software takes advantage of technology previously developed by Parker's research group to improve the speed and quality of halftone and fax transmission. Several software and printer companies have incorporated Parker's technology into devices they have sold around the world, and he holds several patents. The work has been funded by the Department of Electrical Engineering. tr