Security of public key certificate based authentication protocols

The security of authentication protocols based on public key cryptography depends on the validity of the certificate. It is usually assumed that a well deployed PKI can guarantee the validity of certificates through mechanisms such as CRL or OCSP. In reality, such guarantee is not always assured. This paper describes an attack that exploits this certificate validity weakness and breaks some well-known certificate-based authentication protocols, namely the SSL and the TLS protocol. This attack affects the "named-server" version of both protocols, but is ineffective for the "named-server, named-client" version of both protocols. Along with the attack, we also describe how it was discovered as a result of our ongoing research on analysis of authentication protocols using both logic based and model checking based methods.