A simple method of encrypting paper documents so that they cannot be read by the naked eye yet can easily be decrypted without a computer has been devised by MM Comercial of Brazil (WO 03/005634).
A computer creates an apparently random pattern of dots and prints it on a transparent overlay. The original text or picture is then printed onto paper as a pattern of dots, with enough dots missing to make it unrecognisable. When the mask is placed over the original, the two sets of dots combine to recreate the original image. What鈥檚 more, a single decryption mask can be used to view many documents, and to make the encryption tougher, the dots can be coloured and the mosaic separated into more than two sheets.
