Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.2 9/18/84; site hydra.UUCP Path: utzoo!linus!philabs!cmcl2!harvard!think!mit-eddie!cybvax0!frog!hydra!die From: die@hydra.UUCP (Dave Emery) Newsgroups: net.ham-radio Subject: Re: Eavesdropping revisited [How's that again?] Message-ID: <138@hydra.UUCP> Date: Thu, 31-Oct-85 01:05:11 EST Article-I.D.: hydra.138 Posted: Thu Oct 31 01:05:11 1985 Date-Received: Sun, 3-Nov-85 08:01:20 EST References: <154@pyuxv.UUCP> Reply-To: die@hydra.UUCP (David I. Emery) Followup-To: !decvax!frog!die Distribution: net Organization: Charles River Data Systems, Framingham MA Lines: 69 Keywords: encryption shortsightedness Summary: Why wasn't encryption used in cellular standard In article <154@pyuxv.UUCP> craig@pyuxv.UUCP writes: > Congress has a measure under consideration that would >strengthen such privacy law requirements extending protection to >cellular and cordless telephones. Markup is expected, for both the >House and Senate versions of the bill, by early next year. There is a >possibility of enactment by the end of 1986. I have always wondered why the cellular radio standard didn't include digital transmission under (optional?) encryption. Digital transmission would make cellular signals difficult to intercept with scanners or even TV sets, and the hardware required - much like a descrambler for a broadcast tv signal - would be specialized enough so random members of the general public couldn't legally acquire it on the pretext of using it for some legitmate purpose (unlike TVRO's and SSB receivers !!). For a few dollars more the system could supply DES with reasonable key security that would make the cellular link at least as private as the rest of the telephone system. The current transmission method for cellular phones is FM, and the channel spacing is such that there would be plenty of room for a 16 or 32 khz QPSK (or even diphase) adaptive slope (ADPCM) or CSVD transmission of high quality voice. As for performance, I have read some claims that clever demodulators can do as well demodulating digital voice signals near threshold as nbFM. It seems a shame that the designers of a system as sophisticated as the cellular phone system chose not to consider the security issue seriously. I beleive that most of the design work was done in the late 70's when DES chips and LSI PCM chips were at least beginning to appear on the market, certainly any far sighted system architect could have confidently predicted that the required digital hardware would soon be available and eventually be quite cheap. My guess is that low cost in the short term and reduced technological risk dominated their thinking. Perhaps someone on the net can shed some light on why the current fm based system was chosen. The real tragedy is that the proliferation of the current generation of FM based hardware will make it very difficult to convert the whole system over to digital. Perhaps the present transmission sites can be equiped with dual mode radios that would allow subscribers to use digital transmission as an option and thus allow those who understand the risk and want to protect their privacy to enjoy the conveniance and flexibility of roaming cellular phones with a modicum of privacy too. I should think that there might be quite a market for such a higher privacy (and price no doubt) service as people begin to discover that 900 mhz scanners (and some tv sets as Bob Parnass points out) can pick up their fm conversations clearly. Unfortunately, though the NSA has been very active in trying to raise consciousness about security, the more political FCC has yet to authorize secure digital transmission over the current 900 mhz cellular phone frequencies. One would think that the government would get its act together and lead on the issue for once by requiring that all cellular systems be equiped with dual mode capability by some future date. The cost of digital base station transcievers at cell sites and of the required microprocessor systems for key management would be a reasonably small addition to the cost of all the required hardware at cell sites. I suspect that by charging more for a secure service the costs could be recovered (I might add that the systems in the Boston area use microwave links to tie the cells together and those ought to be secured too...). And the digital hardware for mobiles could be implemented in a small number of VLSI chips that ought not to add excessive cost, power consumption or weight to these high tech transceivers. David I. Emery Charles River Data Systems 617-626-1102 983 Concord St., Framingham, MA 01701. uucp: decvax!frog!die