PARA'04 State-of-the-Art
in Scientific Computing
June 20-23, 2004 (Home page)
Updated: February 3, 2004

Historical CRL for Verifying the Signature

Jong-Hyuk Roh, Seung-Hun Jin and Kyoon-Ha Lee
Information Security Research Division, ETRI, Korea
and
Dept. of Computer Science & Engineering, Inha University, Korea
email: jhroh@etri.re.kr

In PKI, when a Certification Authority (CA) issues a certificate, the validity of certificate is limited by an expiration date. But, it may be necessary to revoke a certificate before expiration of its validity period, when a private key is compromised or when a key holder changes identification data (e.g., affiliation). Proper use of a certificate consequently implies not only its formal verification, but also revocation status checking. Then, a mechanism for determining whether a certificate was revoked is needed.

The CA would periodically issue a certificate revocation list (CRL) that listed all of the unexpired certificates that it had revoked. However, the CRL has some flaws. For one, this does not operate in real time. And the CRL is cumulative since every revoked certificate is added to the CRL and kept there until it expires. Thus, the CRL file size can become very large. This means that the communication cost is high. To deal with this problem, a number of revocation schemes have been recently proposed. For example, there are Delta-CRL, CRL DP, CRS, CRT and OCSP.

These schemes mostly supply the latest status information of the certificate. However, it is insufficient. For example, Alice uses her private key to sign a document. Many months later, the validity of Alice¡¯s digital signature is important to Bob. How can Bob determine if the signature was generated when Alice¡¯s certificate was valid or not?

The CRL syntax permits the CA to suspend certificate. Suspension places a certificate on hold, and the CA may take the certificate off hold by removing the entry from a future CRL. The suspension of a certificate makes it quite difficult to retrospectively determine the validity of a signature.

In this paper, we investigate several cases that may happen according to the time of verification and the time of making signature. We point out deficiencies of existing schemes and provide a solution. Our solution is the Historical CRL that can provide the historical information of the certificate status and solve the problem about certificate hold.

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