PKI Interoperability Models (February 2005)
3. Current PKI Interoperability Activity
There are numerous PKI interoperability discussions taking place in international and regional forums. This activity is being driven by government and business requirements to develop mechanisms to ensure disparate PKIs can work together:
Businesses are deploying Public Key Infrastructures (PKIs) to support internal business processes, implement virtual private networks, and secure corporate assets. In addition, most businesses have industrial partnerships with other businesses for economic reasons. If these industrial alliances wish to exploit their internal security capabilities for business to-business (B2B) electronic commerce applications, connection of their corporate PKIs will be required. However, corporate PKIs may implement different architectures, security policies, and cryptographic suites. A flexible mechanism is needed to link these corporate PKIs and translate these corporate relationships into the electronic world.
Unfortunately, there is no single agreed set of the available PKI interoperability models, but some clear trends can be discerned from current discussions and activity.
 William T. Polk and Nelson E, Bridge Certification Authorities: Connecting B2B Public Key Infrastructures, Hastings National Institute of Standards and Technology, September 2001