Path: utzoo!utgpu!watmath!att!ulysses!smb From: smb@ulysses.homer.nj.att.com (Steven M. Bellovin) Newsgroups: news.software.b Subject: Re: public key cryptography to eliminate/detect forged messages Keywords: crypt kerberos usenet cancel Message-ID: <12007@ulysses.homer.nj.att.com> Date: 10 Aug 89 02:16:33 GMT References: <1038@anise.acc.com> Organization: AT&T Bell Laboratories, Murray Hill Lines: 32 Sure, public-key cryptography would work, though the implementation details can get tricky. We knew that way back when, when we designed the very first release of netnews. It deliberately had no control messages because we knew that short of cryptography there was no way to authenticate them. Why didn't we implement one? Well, it's harder than you might think. Bear in mind that what is needed is a system good enough to stand up to a hacker or malicious legitimate user willing to crunch for a week in the background on {spare|stolen} cycles on a large machine, while still being cheap enough to run on a small one. (If I need to, I can use a Cray. I'm not the only one.) It's also unclear what algorithm to use. RSA is patented (though the patent hadn't been granted at the time). Knapsack has been broken. Other schemes are proposed regularly, but their worth is unclear. Incidentally, we don't need public-key cryptography; what we need is digital signatures, i.e., something that provides a (public key) cryptographic checksum without necessarily providing secrecy. The distinction is important; there are a number of algorithms that provide just the signature function. I suspect that the best bet for the near term is to piggyback off of the privacy-enhanced electronic mail being adopted for the Internet. See RFC 1040 for details. An agreement has been negotiated to use RSA (*with* payment of licensing fees, thank you). It may be both technically easy and legitimate given the terms of the agreement with RSA Data Security, Inc., to use much of the same code, formats, etc. Unfortunately, I have not seen any public statement on just how the licensing will work. --Steve Bellovin