PGP Reference
You have found the way to Reference on PGP:
Draft - Multiple Signatures using Security Multiparts - Describes how the Security Multiparts defined in RFC 1847 can be used to transport multiple digital signatures.
PGP Key signing policy of Juergen Nieveler - PGP Key and Key signing policy of Juergen Nieveler.
PGP related RFC - PGP query results in HTML format with tables of contents and crosslinked references
RFC 2015 - MIME Security with Pretty Good Privacy (PGP) - This document describes how Pretty Good Privacy (PGP) can be used to provide privacy and authentication using the Multipurpose Internet Mail Extensions (MIME) security content types described in RFC1847. (M. Elkins / Aerospace Corporation)
RFC 2440 - OpenPGP Message Format - This document describes information needed to develop interoperable applications based on the OpenPGP format.
RFC 1991 - PGP Message Exchange Formats - This document describes the format of PGP 2.x files, i.e., messages that have been encrypted and/or signed with PGP. Replaced by RFC 2440. Help build the largest human-edited directory on the web.