Privacy-enhanced Electronic Mail

Privacy Enhanced Mail (PEM), is a 1993 IETF proposal for securing email using public-key cryptography. Although PEM became an IETF proposed standard it was never widely deployed or used.

One reason for the lack of deployment was that the PEM protocol depended on prior deployment of a hierarchical public key infrastructure (PKI) with a single root. Deployment of such a PKI proved impossible once the operational cost and legal liability of the root and 'policy' CAs became understood.