I created an example to explain to a colleague our discussion at the end of the day regarding multipart/encrypted and thought I'd share it with the rest of you. By requiring S/MIME to use multipart/encrypted, it would make it easy for mailers to use plug-in encrypters/decrypters. The "protocol" parameter would specify which plug-in to use. Since parameters can't (yet) be used in mailcap files to specify a body part viewer, a shell-script front-end might be necessary to read the protocol parameter and execute the specified decrypter. For example, assume the following message based on RFC 1874: To: email@example.com From: Bill Wohler <firstname.lastname@example.org> Subject: test Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----- =_aaaaaaaaaa0" ------- =_aaaaaaaaaa0 Content-Type: multipart/encrypted; boundary="----- =_aaaaaaaaaa1"; protocol="foo/bar" ------- =_aaaaaaaaaa1 Content-Type: foo/bar Control information... ------- =_aaaaaaaaaa1 Content-Type: application/octet-stream Content-Transfer-Encoding: base64 TGludXggMS4xLjU5LiAoUE9TSVgpLgo= ------- =_aaaaaaaaaa1-- ------- =_aaaaaaaaaa0-- and a mailcap (mhn_defaults in MH, grrr!) entry like: mhn-show-multipart/encrypted: /usr/local/bin/decrypt '%f' %a Decrypt would accept 3 parameters (in this case, mhn would pass two filenames for the single %f escape). The first two parameters would be filenames containing the control and encrypted information respectively. The third argument would be `protocol="foo/bar"', which would be used to execute a suitable decrypter which would act upon the two files. Questions: Is this a reasonable example of "plug-in" usage? Is the %a escape common in mailcap files? (Is there a mailcap standard?) Is there a security problem with using intermediary files? Is this why we were shooting towards or did we have a loftier goal of moving more control information into the control block so that the encrypted block might actually be used by different decryption schemes (PGP, S/MIME), but using a convergent technology? Bill Wohler <email@example.com> ph: +1-415-854-1857 fax: +1-415-854-3195 Say it with MIME. Maintainer of comp.mail.mh and news.software.nn FAQs. If you're passed on the right, you're in the wrong lane.