1. A counterfeit document detection system for documents bearing variable strings of characters in at least two fields that are recorded at a document printing station and authenticated at one or more remote authenticating stations, the system comprising: A) printing means at a printing station for printing on a document variable strings of characters in at least two fields; B) a first computer means connected to said printing means for storing information including said variable strings of characters and for communicating said information to said printing means for printing said variable strings of characters on said document; C) unique code generating means connected to said first computer means, said unique code generating means for selecting certain of said characters from said strings of characters in at least two fields and generating therefrom another string of characters that is a unique code characterizing the document bearing said variable strings of characters, said unique code generating means including a secret program means for directing said first computer means to select particular characters, and transforming means for transforming the selected characters into another string of other characters to produce said unique code and for printing said unique code on said document along with said variable strings of characters, said secret program means not accompanying said document; D) a second computer means at a document authenticating station; E) input means connected to said second computer means for entering into said second computer means, at the time of verification of said document and not before, said printed variable string of characters and said unique code read from a document to be authenticated; F) authenticating code generating means connected to said second computer means including said secret program means for directing said second computer means to select certain characters from said printed strings of characters as they appear on said document and transforming said certain characters in the same manner as was performed by said first computer means in generating said unique code; and G) comparator means for comparing said unique code and said authenticating code for rejecting said document when said unique and authenticating codes do not match and for accepting said document when said codes match, whereby said document bears all the document-specific information necessary for verification of said document when said information is used in combination with said program means.
2. The system according to claim 1, in Which said transforming means includes conversion table means for converting each selected character into another character.