Validating Digital Signatures without TTP’s Time-Stamping and Certificate Revocation

In non-repudiation services where digital signatures usually serve as irrefutable cryptographic evidence for dispute resolution, trusted time-stamping and certificate revocation services, although very costly in practice, must be available, to prevent big loss due to compromising of the signing key. In [12], a new concept called intrusion-resilient signature was proposed to get rid of trusted time-stamping and certificate revocation services and a concrete scheme was presented. In this paper, we put forward a new scheme that can achieve the same effect in a much more efficient way. In our scheme, forward-secure signature serves as a building block that enables signature validation without trusted time-stamping, and a one-way hash chain is employed to control the validity of public-key certificates without the CA\u27s involvement for certificate revocation. We adopt a model similar to the intrusion-resilient signature in [12], where time is divided into predefined short periods and a user has two modules, signer and home base. The signer generates forward-secure signatures on his own while the home base manages the validity of the signer\u27s public-key certificate with a one-way hash chain. The signature verifier can check the validity of signatures without retrieving the certificate revocation information from the CA. Our scheme is more robust in the sense that loss of synchronization between the signer and the home base could be recovered in the next time period while it is unrecoverable in [12]. Our scheme is also more flexible in the real implementation as it allows an individual user to control the validity of his own certificate without using the home base