Note: Many topics at this site are reduced versions of the text in "The Encyclopedia of Networking and Telecommunications." Search results will not be as extensive as a search of the book's CD-ROM.

To provide privacy of electronic mail, mechanisms are needed to assure both sender and receiver that messages are confidential, that messages are from an authentic source, that messages have not been altered or corrupted, and that the sender cannot repudiate (disown) the message.

PEM was one of the first standards for securing the text of e-mail messages. PEM was defined by the IETF as a way to encrypt 7-bit text messages. It also defined a hierarchical structure for distributing and verifying digital signatures. PEM specifies a public-key infrastructure for key exchange over large networks like the Internet. However, the specification was deficient and newer standards have been developed, as discussed under "PKI (Public-Key Infrastructure)."

When MIME (Multipurpose Internet Mail Extension) was introduced as a way to add binary attachments to e-mail, PEM became less important because of its support for only 7-bit text messages. PEM was then extended with MOSS (MIME Object Security Standard), a protocol with PEM compatibility and support for MIME attachments. However, MOSS is difficult to implement and use. S/MIME is a de facto standard for securing mail messages that can replace PGP (Pretty Good Privacy) and PEM (Privacy-Enhanced Mail). See "MIME (Multipurpose Internet Mail Extension)" for more information.

Copyright (c) 2001 Tom Sheldon and Big Sur Multimedia.
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