This should be particularly interesting for John Klensin, as it is really a follow-on to discussion last summer on the topic of information theory and spam. On Fri, 13 Feb 2004, Ed Gerck wrote: > > Err, I think that allows you to correct _errors_ in transmission. > > Shannon distinguished messages --or intended information-- from noise. > The distinction beween noise and information is that information is what > the sender wants to send or, alternatively, what the receiver wants to > receive. If the channel is a covert channel, it is fair to assume that > either the sender or the receiver (or both) do not intend it to exist > (otherwise, it would not be a covert channel). Thus, a covert channel > transmits information that can be considered for modeling purposes as a > source of noise. Since the 10th theorem applies to any source of noise, > it also applies here. You are confusing a covert channel with noise. They aren't the same. Antispammers have commonly used an analogy that equates spam with noise and anti-spam efforts as trying to find a "noise filter". The analogy sounds good, but is not accurate, which might suggest a reason why they have failed to find a "filter". Spam isn't unwanted until after the fact: You read it, and then you don't like it. Some people think AC/DC (or rock music in general) is "noise", or commercials are "noise", but they aren't noise from the point of view of information theory, and your real or theoretical radio won't be able automatically filter them out when the DJ plays them, though it will do a good job of filtering out noise. You have to hear/read/see it, decide you don't like it, and complain about it. But you can't build a stereo that won't play rock music or won't play commercials. Perhaps, like the Janet Jackson Breast Baring (JJBB), the station operator will agree with your complaint, and a fuss will be made that won't cost you anthing, except taxes. Spam is essentially the same problem as preventing people from exposing themselves on TV. In a sense, the problem is similar to NP-Complete problems because there are a whole class of problems that are basically the same, and if you could solve one, you could solve them all. Getting back to information theory, Spam is information that the system operator doesn't intend to be sent. It breaks the rules which say not to send this kind of information. Spam (per the definition of a covert channel) is simply a "communication not authorized by the security model". I should probably explain that spam is a multiplexed channel and identify all the necessary parts relevant to information theory, but I think that is fairly obvious, and unnecessary unless you dispute that spam is a channel per the definitions of information theory. People have challenged this, but infrequently. It seems you don't, so I'll skip it. The definition of "covert channel" and the applicability of information theory to spam was discussed on another (osf_alums) list last fall, and some "very smart people" had some things to say about the definition of covert channels in particular, which as I mentioned previously is a term specificly used by OS scientists. Some people thought it inappropriate to use the term "covert channel" outside the context of operating system analysis. There are other terms used in other types of research, but they all are rooted in information theory, and have the same very general implications as a result: On Fri, 8 Aug 2003, Ellis Cohen wrote: > My 1976 paper on Strong Dependency (abridged in SOSP 5 in 1977) was (as > far as I know) the first paper that applied classical information theory > to problems of computer security (see > http://citeseer.nj.nec.com/context/114449/0) and it contains the term > "covert information path" (but I can't find "covert channel" used). I > might possibly even have been the first to use "covert" in the context > of computer security, but I don't think so. It's even possible I heard > Lampson use it (or maybe it was the other way around ...) > > Leo Rotenberg's excellent MIT thesis, "Making Computers Keep Secrets" > was published in Feb 1974. He talks about "information leakage", > "sneaky signalling", "hidden data flows", and talks specifically about > how communication channels (in particular, accounting channels -- that > is, commuication channels used for billing) can be used to spy on data, > but I can't find the word "covert" used anywhere. > > So it's possible that Lampson coined "covert channel" in 1978, but I > suspect he might have used it earlier in his paper "A Note On the > Confinerment Problem" published in the CACM in 1973. > > Citations seem to indicate that Lampson's deifnition of a covert channel > was a channel "not intended for information transfer". And I beleve I > remember that covert channels were used at that time to cover cases in > which there was no cooperation. For example, suppose a spy can observe > the CPU usage of all programs on a computer which contains a top secret > program which is only run when an important secret event occurs. Even > though there is no cooperation (just sloppy security), a covert channel > (access to the CPU usages) provides theinformation about when an > important secret event occurs. > > -- Ellis Cohen On Fri, 8 Aug 2003, Stavros Macrakis wrote: > "Covert channel" has more than one definition. In Lampson's original > article, it referred to channels not intended for information transfer > at all, and thus did NOT include information leaks via the billing > system or via steganography. If I read the NCSC's definition (below) > correctly, it refers to ANY communication not authorized by the security > model (which seems overly broad to me, but...). > > > I suspect [Lampson] might have used it earlier in his paper > > "A Note On the Confinerment Problem" published in the CACM in 1973. > > A Note on the Confinement Problem > Butler W. Lampson > Xerox Palo Alto Research Center > Comm. ACM 16, 10 (Oct. 1973) > > http://citeseer.nj.nec.com/lampson73note.html > > Even when all unauthorized access has been prevented,... [a service] may > leak, i.e. transmit to its owner the input data which the customer gives > it. > ... > The channels [in his examples] fall into three categories: > > * Storage of various kinds maintained by the supervisor which can be > written by the service and read by an unconfined program, either shortly > after it is written or at some later time. > > * Legitimate channels used by the confined service, such as the bill. > > * Covert channels, i.e. those not intended for information transfer at > all, such as the service program's effect on the system load. > > > >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> > > NATIONAL COMPUTER SECURITY CENTER > A GUIDE TO UNDERSTANDING COVERT CHANNEL ANALYSIS OF TRUSTED SYSTEMS > November 1993 > http://www.radium.ncsc.mil/tpep/library/rainbow/NCSC-TG-030.html The only solution so far is "detect and correct". Which, as noted, isn't a very good solution, and we desire a solution that didn't have this characteristic. > Actually, I described a detection AND a correction mechanism. The > correction mechanism uses a correction channel as given by the 10th > theorem. BTW, just sampling 1% of mail might be enough to prevent > misuse to almost 100% confidence. It is still a "whack-a-mole" or "detect and correct" problem. It is not impossible for someone to conduct abuse. What sampling level you need to have to assure a certain degree of compliance depends greatly on the deterrence of the correction method. > > Actually, genuine spam is not outlawed. > > It depends how you define spam. Genuine "spammers" would quibble > with you calling them spammers. I'd call them email senders. > > > Only the spam sent by people who > > are not genuine businesses is outlawed. > > Not true. If a genuine business continues to send me messages > after I unsub, it is spam. The classification of spam is not > based on who sends the message. This is a quibble, or you haven't read the CAN-SPAM act. > > I expect that this abuse is sent > > by a very small group of people. Prosecuting this small group should be > > relatively easy. > > It has not been and it will only get worse. Until last month, there were no tools to prosecute them, except for virus infection. And that isn't taken seriously unless there is fear that the virus caused a major power failure. But in that case, the virus sender is caught quickly and painlessly. > > > Also, users should not have to sue spammers, or have any other burden, > > > in order to protect the users' resources. Imagine if I would have to > > > manage 300 lawsuits a day (the average spam rate that my system cannot > > > automatically detect as spam)? > > > > This is an exaggeration. There aren't 300 unique spammers per internet > > user per day. > > Agreed -- it's an understatement. I believe there are perhaps > 1000x 300 unique spammers per day. 300,000 unique spammers each day, and only 6 billion people in the world. Gee only 20000 days until every one on the planet is a spammer. Yet everyone on the planet doesn't even have email, telephone, or even TV. I wonder if there will be anyone without these things in 50 years. I heard not too long ago that there are _only_ around 100 million on the net. Maybe its now up to 200 or 300 million. So in 3 years, everyone that's on the net will be a spammer. Gee. Maybe we better get moving on the IPv6. ;-)