Evidencing indicia of value using secret key cryptography
View Patent ↗A method and system for dispensing and evidencing indicia by an indicia generating device is disclosed in a system having a plurality of indicia generating devices that have been divided into n groups. Each of the indicia generating devices generates and prints 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 receiving a plurality of verification keys, wherein each one of the received verification keys is encrypted as a function of a respective geographic designation. A plurality of key IDs are also received, where each one of the key IDs is associated with one of the verification keys and is encrypted as a function of the same geographic designation used to encrypt the corresponding verification key. In response to receiving a request to generate an indicium for a media destined for a particular one of the establishments, the indicia generating device evidences the indicium 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 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.
1. A method for dispensing and evidencing postage indicia by a postage generating device (PGD) in a system having a plurality of PGDs that have been divided into n groups identified by a group designation G i , i=1, . . . n, the method performed by the PGD comprising:
(a) receiving by the PGD a master secret key K and a secret key K i from a distribution center over a network after manufacture of the PGD, and storing the master secret key K and the secret key K i in the PGD;
(b) in response to receiving a request to generate an indicium for a mail piece destined for a particular postal destination Dest, generating the indicium;
(c) computing by the PGD a verification key V i Dest as a function of the secret key K i and the postal destination;
(d) computing a key ID I i Dest as a function of the master secret key K and the postal destination;
(e) using by the PGD the computed verification key V i Dest to create a digital signature for the indicia; and
(f) digitally signing by the PGD the indicia by including the digital signature and the computed key ID I i Dest on the indicia.
2. The method of claim 1 further including the step of computing each verification key V i Dest as a one-way function H of the PGD group key K i and a designation of the postal destination:
V i Dest =H ( K i ,Dest ).
3. The method of claim 2 further including the step of using ZIP codes to designate the postal destination.
4. The method of claim 3 further including the step of computing each of the key ID's as a one-way function H of the PGD group, G i , the master secret key, K, and a designation of the postal destination, Dest:
I i Dest =H ( K,Dest,G i ).