Inconsistent deployments . Some PKI deployments use one key pair for all security services supported by the infrastructure. Others use one pair for authentication and confidentiality and another for digital signatures. Lack of standard practices in this arena makes it difficult to institute best practice guidelines over credentials management, security, backup, expiration, etc. Technical diversity .
Technology is available to deliver the needed interoperability.
And we agree on the applicable protocols and how they are implemented and used. Vendors like to compare today's PKIs to the early days of e-mail, a time when electronic messaging faced many of the same challenges PKI is grappling with today. Just as e-mail eventually became a universally accepted method of communication, vendors hope PKI will achieve similar mainstream status in the near future. Only time will tell.