A number of serious security issues have already occurred with the rapid deployment of electronic transaction. One approach to guaranteeing security is the public key infrastructure (PKI). PKI provides a structure of trust among its users or principals. However there are serious PKI implementation issues as different countries and different organizations may adopt different security policies and implementations. This raises the question of interoperation between these various implementations. In the paper, the author proposes a new solution using VA (Validation Authority) to achieve the digital certificate validation and resolve the general PKI interoperation problem.