Patent ID: 7058614

Claim:
A method of producing and checking franking marks, comprising the steps of: storing a set of unique bit strings in a first memory in a central office that is connected to a plurality of terminals; making one or more of the unique bit strings available to at least one terminal of the plurality of terminals; at the central office, receiving from the one terminal a copy of the unique bit string made available thereto in combination with an identification code and storing in a second memory at the central office the copy of the unique bit string in combination with the identification code received from the one terminal; reading of a franking mark after the franking mark has been printed on a document, the franking mark including an encoded identification code and an encoded unique bit string; decoding the franking mark to render a decoded identification code and a decoded unique bit string; checking whether the decoded identification code is correct by comparing the decoded identification code to the identification code stored in the second memory; and checking whether the decoded unique bit string is valid by comparing the decoded unique bit string to the unique bit string stored in the second memory.