Patent ID: 6847951

Claim:
A method for controlling, and distributing information between a digital postage meter and a certifying station operated by a certifying authority CA for publishing information, so that a public key Key DM *P of said digital postage meter can be determined by a party seeking to verify indicia printed by said digital postage meter from said published information with assurance that said public key Key DM *P has been certified by said certifying authority CA, said method comprising the steps of: a) defining and publishing a finite group [P] with a binary operation [+] and publishing a particular point P in said group; b) defining and publishing a binary operation K*p, where K is an integer and p is a point in said group, such that K*p is a point in said group computed by applying said operation [+] to K copies of said point p; c) controlling a certifying station to publish a certificate OMC DM for said digital postage meter, wherein; OMC DM =( r DM +r CA )* P; and wherein r DM is a random integer generated by said digital postage meter and r CA is a random integer generated by said certifying station; d) controlling said certifying station to publish a message M; e) controlling said certifying station to generate an integer I DM , and send said integer to said digital postage meter, wherein; I DM =r CA +H( M )Key CA ; and wherein H(M) is an integer derived from said message M in accordance with a publicly known algorithm H and Key CA is a private key of said certifying authority CA; f) publishing a public key Key CA *P for said certifying authority CA; and g) controlling said digital postage meter to compute a private key Key DM , Key DM =r DM +I DM =r DM +r CA +H ( M )Key CA ; and h) controlling said digital postage meter to print an indicium and digitally sign said indicium with said key Key DM ; whereby i) said verifying party can compute said user's public key Key DM *P as Key DM *P=OMC DM +H( M )Key CA *P =( r DM +r CA )* P+H ( M )Key CA *P from knowledge of H, M, [P], said public key Key CA *P, and OMC DM .