Infrastructure

[nobody@alumni.cco.caltech.edu]

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Some time back there was some debate here about whether MIME
("Multipurpose Internet Mail Extensions") features could be exploited
to make encryption easier to use.  I didn't pay much attention at the
time, because I didn't know anything about MIME.  But then a couple of
weeks ago John Gilmore posted about Metamail, a software system
designed to make it easy to integrate MIME into commonly-used mailers.

I've played with Metamail a bit, and I do think this could be a good
approach.  Metamail basically performs a mail-sorting function,
automatically passing mail which has the MIME "Content-type" header to
a filter or display program based on a very flexible "mailcap" file.
To add PGP (or PEM, or RIPEM) support would be a matter of defining a
Content-type header for this application, then creating the
appropriate 1-line entry in the mailcap file.  This does sound like a
pretty easy way to add this capability.

The nice thing is, Metamail has already done the work of figuring out
how to patch a whole bunch of different mailers to add this support.
By using metamail we would be leveraging off this already-existing
work.  Here are some excerpts from the "mailers.txt" file that comes
with the distribution, written by Nathaniel S. Borenstein:

>  Abstract
>  
>  It is surprisingly easy to use the RFC1049 "Content-type" header to turn
>  virtually any mail reading interface into a multi-media mail reading
>  interface.  Mail readers are simply modified to use the new "metamail"
>  program whenever they receive non-text mail.  The metamail program is
>  itself easily customizable by the use of a "mailcap" file that specifies
>  the media types supported by a given site or user.  Given the existence
>  of the metamail program,  this document explains how to add multimedia
>  support to sixteen very different mail reading programs, including all
>  of the most popular UNIX mail reading programs and (so far) one DOS mail
>  reading program.  
>  [...]
>  The Basic Idea
>  
>  Basically, there are only two things you have to do to each mail reading
>  program:
>  
>  1.  Make the mail reader notice the special header ("Content-type") that
>  marks a message as a non-text message.  (In the case of mail readers
>  that already understand certain content-types, such as Andrew, the mail
>  reader must be modified only to deal with the content-types it does not
>  already know how to handle.
>  
>  2.  When the special header appears, instead of (or, if it's much
>  easier, in addition to) showing the user the body of the message, the
>  mail reader must send that body off to the metamail interpreter.  The
>  metamail interpreter includes features that deal with the diverse
>  situations of terminal-oriented and window-oriented mail readers.
>  [...]
>  A Variety of Mail and Bulletin Board Reading Interfaces 
>  
>  With this document, you can patch all of your site's mail reading
>  interfaces to support whatever multimedia formats are deemed useful at
>  your site.  This means that those who regularly use the multimedia tools
>  can begin to send mail in those formats freely, without worrying about
>  the ability of any local user to interpret the mail.  It is my intent to
>  make this document exhaustive; as time goes on, I hope it will grow to
>  include an ever widening set of mail reading interfaces.  Currently it
>  includes all of the mail reading interfaces that I know to be in use
>  anywhere in Bellcore's research laboratories.
>  
>  Currently this document describes how to add support for the following
>  mail readers:
>  
>        Berkeley Mail (/usr/ucb/Mail, /usr/ucb/mail, and Tahoe mail)
>        SunMail (another version of Berkeley mail, but rather different)
>        Xmail (an X11 interface to Berkeley mail)
>        Mailtool (older versions of a SunTools interface to Berkeley mail)
>        Imail (Bellcore MICE mailer)
>        PCS readmail/rdmail/sreadmail (another Bellcore mailer)
>        MH -- Rand Message Handling System
>        XMH -- X11 Interface to Rand Message Handling System
>        Rmail -- GNU Emacs mail reading package
>        VM -- Another GNU Emacs mail reading package
>        MH-E -- Yet another GNU Emacs mail reading package (GNU interface to MH)
>        CUI -- Andrew low-end mail reader 
>        VUI -- Andrew termcap-based mail reader
>        Messages -- Andrew multimedia mail reader
>        BatMail -- Andrew Emacs mail-reading interface
>        Elm -- Mail reader from HP.
>        Mush -- Yet another popular mail reader
>        Msgs -- simple Berkeley bulletin board reader
>        UUPC --a mail reading program for MS-DOS
>        TRN -- a threaded netnews reader.
>  
>  
>  If you have mail readers that are not dicussed here, you will still
>  probably find some of this code useful as a model.  If you develop a
>  patch for some other mail reader, and you send it back to me, I'll
>  include it in future versions of this document.

I am very impressed with the range of mailers covered here.
Unfortunately, access to source is needed for most of the patches.
But my guess would be that patched versions would become available
even to people who don't have source.

I'm not really sure what is happening with PGP specifically in terms
of MIME.  I think there has been some work done with PEM integration.
There doesn't seem to be any reason why these programs can't integrate
nicely with MIME, and this Metamail package looks like it might be the
most cost-effective way of getting widespread encryption into use.

Hal

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