A Method for Detecting the Exposure of OCSP Responder’s Session Private Key in D-OCSP-KIS

Abstract

D-OCSP-KIS proposed by Koga and Sakurai not only reduces the number of OCSP Responder’s certificate but also offers the certificate status validation about OCSP Responder to the client. Therefore, D-OCSP-KIS is an effective method that can reduce the communication cost, computational time and storage consumption in client, but it has some problems. In case an attacker accidentally acquires an OCSP Responder’s session private key in a time period (e.g., one day), she cannot derive any other OCSP Responder’s private key unless she obtains master private key. And she cannot derive the hash value of previous period because the hash value is impossible in inverse computation. But, the attacker can disguise as the OCSP Responder in the time period unless the OCSP Responder recognizes. She can offer the wrong response to the client using the hash value intercepted. And the server and user on E-commerce can have a serious confusion and damage. And the computation and releasing of hash chain can be a load to CA. Thus, we propose a method detecting immediately the exposure of OCSP Responder’s session private key and the abuse of hash value in D-OCSP-KIS. In our proposal, the hash value is only used one time for the status validation of OCSP Responder’s session private key and the load for computation of X-chain in CA is distributed to each OCSP Responder.