PGPMIME

PGPMIME, often written as PGP/MIME, is a standard for applying OpenPGP encryption and digital signatures to MIME-encoded email. It specifies how encrypted or signed OpenPGP data should be packaged within MIME parts so that ordinary email infrastructure can transport confidential messages without requiring special handling by mail servers.

The purpose of PGPMIME is to provide end-to-end confidentiality and authenticity for email. Senders use the recipient’s public OpenPGP key to encrypt the message and their own private key to create a signature. Recipients use their private key to decrypt and verify the signature. The format supports encrypting the message body as well as attachments, using multipart MIME structures and specific content types to carry the encrypted payload and the accompanying metadata.

A typical PGPMIME message uses multipart/encrypted or multipart/signed structures. The encrypted content is transported as an OpenPGP payload, usually embedded in a MIME part with a content type such as application/octet-stream, while preparatory headers indicate the presence of OpenPGP data. OpenPGP toolchains, such as GnuPG, are commonly used to implement these operations in mail clients and automation scripts.

History and status: PGPMIME emerged in the OpenPGP ecosystem during the late 1990s and early 2000s to integrate PGP encryption with MIME email. It has been implemented in a range of mail clients and libraries, often via plugins or built-in OpenPGP support. Interoperability and user experience have varied across different clients and versions.

See also: OpenPGP, MIME, S/MIME, email security.