John Gilmore <gnu@toad.com> (05/25/90)
I heard rumors of a digital cellular telephone standard among DSP folks, and tracked them down. The draft standard is called "IS 54" and its project number is 2215. It is currently not available anywhere; they ran out of the drafts, and it won't be published for about a month. This is your standards bureacracy serving *you*! The draft will eventually be published for public comment by EIA in DC (202 457 4900). The contact person there is Eric Schiml in the Telecommunications Industry Association upstairs, at +1 202 457 4990. The chairman of the committee is Peter Nurse of Novatel, at +1 403 295 4673. The description I have heard of the standard is that it is being rushed through in order to make more capacity in the cellular systems in major metro areas. By DSPing voice down to 8Kbits/sec, they can put three separate conversations on each existing cellular channel. Of course, the resulting voices are not nearly as intelligible, and it's probably all but useless for modem traffic. The three conversations are time-multiplexed onto the channel by synchronizing the three cellular phones to alternately transmit 5ms frames such that, when received at the cell after the speed-of-light transmission delay, they occur at different times and thus don't interfere. The standard makes no provision for data traffic and no provision for encryption, even though it is digital end-to-end. The engineers I've spoken with seem to think that its "privacy" will be improved because it's digital, i.e. a scanner won't be able to decode the interleaved binary signal. Of course, each phone built to this standard will have the circuitry to do that, and nobody will modify the ROMs or improve the scanners. More security-by-obscurity. I originally wanted to track down the committee to discuss the requirements of Dynabooks for reliable, nationwide, mobile digital data service. But these folks aren't doing anything like that. In fact, one engineer told me he thought Dynabooks were a bad idea because "people shouldn't be reading while they are driving"!!! The whole idea is to sell more yak-wuile-you-drive to yups, they don't have any idea where the real portable digital markets are at. Real workstations will be palm-sized and portable in 1993 or so, long before the telcos are ready to network them *cheaply* in an office or neighborhood while having them able to remain online on the net (at a price) while traveling all over the country. What hacker, stockbroker, student, reporter, ... would be without one? Anybody got an angle by which we can bypass the telcos and do it right while they blunder? The plan is to reallocate some of the current analog cellular frequencies for this IS 54 bastard digital cellular service, in crowded metro areas. Probably the small towns would never get this equipment. But what is worse is that the act of deploying it in a metro area will REDUCE the number of analog frequencies available. The people who already have cellular phones will get WORSE congestion and fewer frequencies. The people who buy new digital cellular phones will get shitty voice quality and phones that won't work at all in minor markets, or for modems or fax machines. The folks who want real mobile digital telecommunications, even at phone company prices, won't get anything. Ditto the folks who want real privacy on mobile phones. (Remember Heinlein's "hush and scramble" features in every phone? "We have the technology" -- we just aren't deploying it.) The only ones who win from IS 54 are the cellular carriers (who expand their customer base without deploying more cells) and the phone makers (who make people buy another phone as they crowd more early adopters into fewer analog channels). And guess who's writing this standard?
"Christopher J. Pikus" <cjp%megatek.UUCP@ucsd.edu> (05/26/90)
From article <8244@accuvax.nwu.edu>, by gnu@toad.com (John Gilmore): > I heard rumors of a digital cellular telephone standard among DSP > folks, and tracked them down. > The draft standard is called "IS 54" and its project number is 2215. > The standard makes no provision for data traffic and no provision for > encryption, even though it is digital end-to-end. The engineers I've > The only ones who win from IS 54 are the cellular carriers (who expand > their customer base without deploying more cells) and the phone makers > (who make people buy another phone as they crowd more early adopters > into fewer analog channels). And guess who's writing this standard? An alternate path being explored is a joint project between Pac Bell Cellular in Los Angeles and Qualcomm in San Diego. I had an opportunity to view a technology demonstration last novenber. They are using something called CDMA (Code Division Multiple Access) that uses a technique similar to sattelite communications (Qualcomms expertise). All transmitters use the same frequency with no time division; each one running with output power down at the noise floor. Each phone convolves their voice data with a special 32 bit number which a digital modem at the other end searches for. Thus each phone is secure from each other (different keys); the others look like noise to each phone. As for datacomm, the data bandwidth is flexible, you pay for what you need, (with tradeoff in quality/datarate). i.e. 8/16 kbs for voice and 64 kbs for data. The bandwidth limitation is soft since as the channel hits capacity, the b.e.r. will slowly climb. At the technology demonstration, Pac Bell was saying that if they alloc'd 10% of their service (42 channels) to this digital, they could increase capacity by a factor of 2-3 FOR THE WHOLE SERVICE. The people at Qualcomm were saying that a phone could be built that swings both ways; current technology analog and this digital service with the addition of a few DSP chips. It appears that Pac Bell doesn't have time to wait for a standards commitee and decided that an early deployment of a superior system will create a de-facto standard. Regards, Christopher J. Pikus, Megatek Corp. INTERNET: cjp@megatek.uucp San Diego, CA UUCP: ...!uunet!megatek!cjp
gnu@toad.com (John Gilmore) (05/29/90)
One of the engineers I spoke with about the digital cellular stuff wants it made clear that his opinions are only opinions, not word from on high. My statement that I spoke with "engineers" make him think that people will believe they're facts. Alas, if only people took my pronouncements as fact because I'm an engineer... So far nobody is claiming that the privacy of IS 54's digital cellular system is really great, just that it's slightly better than analog cellular. What burns me is that they could have made it *really great* with relatively trivial spec and software changes (encryption) but didn't bother. (Yes, the changes are "relatively" trivial if you examine the protocol they are running here.) He also wants a chance to retract the comment about Dynabooks and driving; given that a large majority of the cellular phones are currently sold for cars (my guess -- anyone have figures?), I can see why he would have equated cellular with car.
boomer@athena.princeton.edu (Don Alvarez) (05/29/90)
In article <8372@accuvax.nwu.edu> gnu@toad.com (John Gilmore) writes: >So far nobody is claiming that the privacy of IS 54's digital cellular >system is really great, just that it's slightly better than analog >cellular. What burns me is that they could have made it *really >great* with relatively trivial spec and software changes (encryption) >but didn't bother. (Yes, the changes are "relatively" trivial if you >examine the protocol they are running here.) I have no idea what protocol they are running, but I do know that creating a system that allows for secure and trusted communications between large numbers of remote devices is never trivial. Providing *encrypted* communications is trivial (rec.funny readers use rot-13 "encryption" all the time, for example) , but providing *secure* and *trusted* communications is. Secure communications mean that only the sender and the intended recipient can read (or in this case listen to) the communication. Trusted communications add caveats that one can detect interuption of service, replay or delay of messages, etc. The important point for a cellular phone link is that encrypted does not mean secure. If you and I wanted to exchange encrypted mail over the internet, we'd have to first agree on and somehow exchange our encryption key without anyone else discovering it for it to be secure. The same is true for cellular phones, only there the key exchange has to be automatic and transparent to the user. How do your phone and my phone agree upon and exchange an encryption key without allowing eavesdroppers to pick up the key? We can't just use public key encryption techniques, because of the following senario: A wants to call B. A says "I need B's public key". C hears the request, and quickly replies "B's public key is foo". C then says "I need B's public key," and waits for B to reply "My public key is bar." A now tries to talk to B. A encrypts the communication using foo, and sends it out. C decrypts it (since C knows how to decrypt foo), copies it, and reencrypts it using bar (which only B knows how to decrypt). B recieves it, decrypts it, and says "I just got a message from A which was encrypted in a way that no one else can decrypt, so it is secure." Likewise, C can catch B request for A's public key and listen to the return half of the call. Somehow, your phone and my phone need to already share a unique key with each other inorder to exchange the key they will use in their communications. That is a chicken and egg problem. The solution, clearly is to have a secure "directory server", which shares a different unique key with every phone in the system. This is a reasonably tractable solution (the number of keys grows only with N, each phone needs only a single key, and distribution of that key can be done when the phone is manufactured), and forms the basis of MIT's Kerberos system for secure and trusted logins to Unix boxes. (<- Actually, Kerberos uses secret key encryption rather than public key encryption, because the security of the method is unaffected and a careful accounting of messages reveals that more packets need to be exchanged to start up a conversation using public key than is needed to start up one using secret key). The problem is that the directory server is now a tremendous single point of failure. Anyone who cracks any directory server anywhere instantly renders the entire security algorythm null and void. Worse, *every phone* would have to be sent back to the manufacturer to get a new secret key burned in (otherwise there would be no way to trust that the new key was not intercepted if it was reprogrammed remotely). That would be prohibitively expensive, so it would never happen. But we all know that somewhere out there is a nasty who would manage to crack into one of these servers (you've got to admit they'd be real attractive nuisances). Now you have a system that everyone believes is secure, but actually provides little or no more real security than current cellular phones. In short, providing secure and trusted communications over a "hostile" network is not trivial, and in my opinion providing a false sense of security about ones communications is worse than providing no security. don alvarez Princeton Univ. Physics Dept. (609) 924-3039
reilly@uunet.uu.net (Patrick L. Reilly) (05/30/90)
If you want to compare the various upcoming cellular developments, look up "What's Ahead Worldwide for Digital Cellular", by A. Slekys, in the May, 1990 issue of Mobile Radio Technology.