A method and system for evidencing payment of indicia using secret key cryptography
is disclosed. The method and system include a plurality of indicia generating devices
that are divided into groups 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 and system include
assigning a plurality of verification keys to each indicia generating device in
each of the groups, wherein each of the verification keys assigned to each of the
groups is encrypted as a function of a respective geographic designation. A key
ID is associated with each of the verification keys and is encrypted as a function
of the same geographic designation used to encrypt the corresponding verification
key. After the verification keys and key ID's are assigned, each one of the establishments
receives the verification keys and the key ID's that were encrypted as a function
of the geographic designation associated with the establishment. When generating
indicia for media destined for a particular one of the establishments, the indicia
generating devices evidence the indicia by generating one of the verification keys
and the corresponding key ID assigned to indicia generating device's group based
on the geographic designation associated with the particular establishment, and
uses the generated verification key to create a digital signature. The indicia
generating devices digitally sign the indicia by including the digital signature
and the generated key ID in the indicia. Upon receiving the media at the particular
establishment, the indicia on the media is verified by 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.