Path: utzoo!utgpu!water!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!mailrus!uwmcsd1!ig!agate!ucbvax!hplabs!hplabsz!taylor From: taylor@hpdstma.hp.com (Dave Taylor) Newsgroups: comp.mail.elm Subject: Mail Encypherment Message-ID: <2085@hplabsz.HPL.HP.COM> Date: 6 Jul 88 17:05:57 GMT Sender: taylor@hplabsz.HPL.HP.COM Organization: HP University Grants Program @ The Pacific Technology Park Lines: 48 Paul Vixie and I last night had a chance to chat about security and electronic mail, and along the way I decided that it would be perhaps useful for the current discussion in this group for me to expound on my motivations for adding the "[encode]/[clear]" feature to the Elm Mail System. Basically, I don't believe that there are any really robust encypherment systems that are quick and painless to use. That's okay, though, because the real reason one wants to encode mail is to prevent unauthorized browsing of the contents *in transit*. That is, if someone *really* wants to read your email, either along the way or once it's arrived, then they *can* do so. The `cryptbreakers workbench' package is widely available, for example, and it is reputed to be able to break the crypt(1) function that is shipped with Unix (crypt is a partial implementation of the DES encryption algorithm, using a shorted [simpler] 52 bit key rather than the original [as designed at IBM] 64 bit key. BTW: I once talked to Dennis Ritchie about whether the simpler implementation was a `plot by the NSA' as widely believed and he laughed...) Anyway, the point is that I think the real goal of any sort of encypherment mechanism is to stop the unauthorized, lazy browsing of spooled mail flowing from machine to machine. There are people out there who will, when bored, type commands like "more /usr/spool/mqueue/df*" in the hopes of finding something interesting... The best algorithm I came up with for this purpose, actually, was a shifting rotation scheme; instead of the +13 rotation cipher (aka rot13) the cipher stepped from +1 to +25 then down to +1, then down to -25 then back. (a very simple mathematical progression, obviously). The criteria for this were simple; fast, simple, and portable. I *do* think that it would be nice to leave the option of alternating paragraphs of hidden text and clear text too. Anyway, back into my corner now... ;-) -- Dave Taylor ps: You will note I do not use "encryption" in this article. When last in France working I was told by them, quite reasonably, that encryption had "crypt" as a basis, and in French that isn't such a lovely thought, so 'encypherment' is the more widely accepted international word to use in this context.