The OPENPGPKEY DNS record is specied in RFC 7929. The localpart of the uid is encoded as a DNS label containing the hexdump of the SHA-256 hash of the utf-8 encoded localpart, truncated to 28 octets. Normally the "Standard" output format should be used. The "Generic Encoding" output format is provided to help work with older DNS software that does not yet understand the OPENPGPKEY record type.