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there is no problem. However, if Alice has to deal with this certificate, Bob must
wait until she comes back from her vacation. We claim that the acceptor should
take care of certificates not satisfying acceptor's recency requirements. This is
different from Rivest's approach [12]. Another advantage of our approach is that
Alice does not need to know Bob's recency requirements. If Bob changes his re-
cency requirements very often or he wants his recency requirements confidential,
our approach will be more promising.
Requirement 6: New Certificates Are the Best Evidence.
Rivest argued
that the simplest form of recency evidence is just a (more-) recently issued
certificate [12]. Fox and LaMacchia pointed out that the response to a real-time
query is just another certificate [2]. Since the computational costs required to
generate an OCSP response and to issue a new certificate are the same, we prefer
to issue a new certificate as a response to a real-time query. However, this re-
issuance technique does not increase CA's risk because the new certificate has
the same expiration time as the queried certificate.
Requirement 7: Reuse of the Existing Certificate Issuance Mecha-
nisms and Infrastructure.
Fox and LaMacchia attested that we had better
leverage existing syntax, message formats and infrastructure as opposed to cre-
ating new messages [2]. They showed that the same syntax could be used to issue
a new certificate and to generate an OCSP response. We move one step further;
a new certificate will be used as a response to a real-time query and the new cer-
tificate can replace the queried certificate. To reuse the existing infrastructure,
we will abstain from introducing new agents such as suicide bureaus.
Requirement 8: Small Computational and Communicational Load.
While online certificate status checking gives the acceptor satisfactory real-time
information, CA suffers from a heavy computational and communicational work-
load. Fox and LaMacchia's system improved OCSP by using the same syntax
for a certificate and an OCSP response, but the number of OCSP responses
generated by CA did not decrease [2]. To mitigate CA's workload, we will re-
duce the number of CA's responses and total communication passes. In most
environments, our system will show a better performance than OCSP.
In the next section, we will propose ACSP, an advanced online certificate
status checking protocol. ACSP is constructed on the above design principles.
After we explain the mechanism of ACSP, we present an analysis of ACSP.
It will be shown that ACSP is more flexible and ecient than OCSP in most
environments.
3 ACSP
3.1 Mechanism
We adopt the model presented in [2] as a typical financial transaction model.
There are three parties of interest: Alice (the signer who sells the financial trans-
