| 摘要 |
<p>A method and system for generating messages from which it can be verified that a variable does not exceed a predetermined limit. The message can be a postal indicium. A message originator, which can be a postage metering system, receives a message in the form R<-k)<T), where R is a trapdoor function, K is an integer equal to the limit, and T is a plain text, from a data processing center which maintains the inverse function R<-1> in secrecy. The message originator computes Sm = R<m)<R<-k)<T), where m is a current value of the variable, and incorporates Sm into the message. A verifier verifies that m < K by confirming that R<k-m)<Sm) = T. The verifier cannot compute R<k-m)<Sm) for m < K since it does not have R<-1>. For the same reason the originator cannot compute R<-k')<T), k' > K, from R<-k)<T). <IMAGE></p> |
