Path: cantaloupe.srv.cs.cmu.edu!das-news.harvard.edu!ogicse!uwm.edu!zaphod.mps.ohio-state.edu!howland.reston.ans.net!sol.ctr.columbia.edu!news.cs.columbia.edu!ji From: ji@cs.columbia.edu (John Ioannidis) Newsgroups: sci.crypt Subject: Re: Source of random bits on a Unix workstation Message-ID: Date: 15 Apr 93 21:57:55 GMT Article-I.D.: cs.C5Jp0K.4p5 References: <897@pivot.sbi.com> Sender: news@cs.columbia.edu (The Daily News) Organization: Columbia University Department of Computer Science Lines: 35 In article so@eiffel.cs.psu.edu (Nicol C So) writes: >In article <897@pivot.sbi.com> bet@sbi.com (Bennett Todd @ Salomon Brothers Inc., NY ) writes: >>This came up because I decided to configure up MIT-MAGIC-COOKIE-1 security >>for X11R5. For this to work you need to stick some bits that an intruder >>can't guess in a file (readable only by you) which X client applications >>read. They pass the bits back to the server when they want to establish a >>connection. >> >>... >>What I settled on was grabbing a bunch of traffic off the network. >>Basically, I ran >> >> etherfind -u -x greater 0|compress >> >>and skipped over 10K of output, then grabbed my bits. As best I can tell, >>these are bits that can be expected to be reasonably uniformly distributed, >>and quite unguessable by an intruder. > >For your application, what you can do is to encrypt the real-time clock >value with a secret key. For a good discussion of cryptographically "good" random number generators, check out the draft-ietf-security-randomness-00.txt Internet Draft, available at your local friendly internet drafts repository. A reasonably source of randomness is the output of a cryptographic hash function (e.g., MD5), when fed with a large amount of more-or-less random data. For example, running MD5 on /dev/mem is a slow, but random enough, source of random bits; there are bound to be 128 bits of entropy in the tens (or hundreds) of megabytes of data in a modern workstation's memory, as a fair amount of them are system timers, i/o buffers, etc. /ji