Patent ID: 6934839

Claim:
A method for evidencing payment of indicia using secret key cryptography in a system including a plurality of indicia generating devices that are divided into groups, each group corresponding to a respective geographic designation, each of the indicia generating devices for generating and printing indicia on a media that is to be received at a plurality of establishments, wherein the establishments are associated with different geographic designations, the method comprising: (a) assigning a set of verification keys from among a plurality of verification keys to each indicia generating device in each of the groups, wherein each set of verification keys assigned to the groups is encrypted as a function of respective geographic designations; (b) associating a key ID with each of the verification keys and encrypting each key ID as a function of the same geographic designation used to encrypt the corresponding verification key; (c) distributing to each one of the establishments in the respective geographic designations via the network, the set of verification keys and associated key ID's that were encrypted as a function of the geographic designation associated with the establishment; (d) assigning to each group of indicia generating devices, at least one respective secret key from a set of secret keys, and distributing the assigned secret key to each indicia generating device in each group of indicia generating devices; (e) using one of the indicia generating devices to generate indicia for media destined for a particular one of the establishments, and evidencing the indicia by (i) generating one of the verification keys and the corresponding key ID assigned to indicia generating device's group as a function of the assigned secret key and the geographic designation associated with the particular establishment, and (ii) using the generated verification key to create a digital signature, and digitally signing the indicia by including the digital signature and the generated key ID in the indicia; and (f) upon receiving the media at the particular establishment, verifying the indicia on the media using the key ID on the indicia and the distributed verifications keys to compute a digital signature, and comparing the computed digital signature with the digital signature on the indicia.