The Risks Digest

The RISKS Digest

Forum on Risks to the Public in Computers and Related Systems

ACM Committee on Computers and Public Policy, Peter G. Neumann, moderator

Volume 17 Issue 66

Tuesday 23 January 1996


o Homebanking NonSecurity demo
Klaus Brunnstein
o Security hole in SSH 1.2.0 (RISKs of being "too careful"?)
Barry Jaspan
o Re: Floating Point Numbers
Wade Bowmer [2]
o Re: RISKS of stolen UN computers
Dave Scott
o Cost to crack Netscape Security falls...
A. Padgett Peterson
o Re: Single computer breaks 40-bit RC4 in under 8 days
Gary Weimer
o Re: Japanese fighter plane shot down another plane
Mickey McInnis
o Re: cryo-risks
Lindsay F. Marshall
o Robots going crazy
Bertrand Meyer
o Re: Hey, your mailing list is sending me viruses!
Alan K. Jackson
Joe A. Dellinger
o Re: AOL E-mail crashes
Doug Bostrom
o E-mail spamming risk
Dan Zerkle
o "Learning Machines" and "Learning People"
o "Learning machine" spam
Martin Kealey
o ABRIDGED info on RISKS (comp.risks)

Homebanking NonSecurity demo

Klaus Brunnstein <>
Tue, 23 Jan 1996 17:32:56 +0100

A German private TV channel (SAT 1) displayed, Monday Jan.22 night (10 pm), a demonstration of how easily homebanking may be attacked in Germany. In this demo, a person used T-Online (a navigation tool similar to CompuServe) to send his ID, PIN, the amount to be transferred (500 DM) and the account to which to transfer, plus a transaction number (TAN) via telephone line. All these data were intercepted on a portable connected to the user's phone line in the basement of the building (indeed, most telephone boxes are rarely locked). Actions of the customer and the "hacker" were shown in parallel, so one could see all data (including PIN which was not displayed on the Customers' screen) on the hackers' display. Before the customer could start the booking process on the bank computer by sending the requestor, the hacker interrupted the telephone connection. As he now possessed all relevant "secret" information of the user, he now started an order to transmit 5,000 DM from his victim's account to another one, successfully (as the customers' vouchers proved. After the demo (about 10 minutes), a short interview (with the author of this report) discussed evident risks; it was made clear that software solutions are available since some time, to replace the old PIN/TAN structure with digital signatures and to encrypt sensitive data using asymmetric encryption.

Risks? Presently, there are several risks in telephone-based homebanking. First, ALL sensitive information is transmitted in cleartext. Secondly, interception of line-based communications of German Telekom is easily possible at several sites, from the basement of a customers' house where lines from different customers are collected in a unit, to units collecting lines from several blocks, streets etc. Thirdly, in contracts between banks and customers, the latter will often have difficulties to prove that an order carrying their personal ID, TAN etc was NOT issued from them, esp. when there is evidence that the order came from the customers' telephone line (though not from his telephone :-). Customer protection (both technically and legally) therefore requires immediate action, as Chaos Computer Club commented in press.

Interestingly, German banks offer enterprises a secure solution based on RSA-licensed encryption software. So far, this is NOT offered to private customers as it canNOT interoperate with T-Online. Financial institutions are discussing presently a solution (either with a chipcard including sort of DES or a solution using an RSA-implementation with 784 bit key, which may be distributed via diskettes) but it is unclear when this solution will be available. As long as such solution is not available, "every day may become payment day even for the most lousy hackers" as one German newspaper (TAZ) wrote.

Klaus Brunnstein (Jan.23,1996)

Security hole in SSH 1.2.0 (RISKs of being "too careful"?)

Barry Jaspan <>
Thu, 18 Jan 96 12:19:25 EST

I found a security hole in the ssh client of SSH 1.2.0 ("Secure Shell", a public-key based drop-in replacement for rlogin, rsh, and rcp). Very briefly, the bug allows any user on a system to obtain that host's secret key (undetected) and thereafter masquerade as that host from anywhere on the net until the key is changed. Anyone that is interested in details of the vulnerability can contact me or the ssh mailing list (

This bug is RISKS material because of what caused it. The ssh client has a mode in which it reads and uses the host's secret key for authentication. The secret is installed in /etc and readable only by root, so ssh has to be setuid-root to access is. Naturally, since this is a security system, the author went to considerable effort to make sure the program did not actual use its root privileges any more than absolutely necessary. Generally, that's a good idea.

The problem in this case is that ssh gives up its root privileges TOO SOON. The flow of control looks like this:

acquire root privs
read secret key
release root privs
use secret key
erase secret key from memory

The result is the host's secret key is still in memory when the program releases its root privileges, making it quite easy for a user obtain that information. Presumably, it would be much harder to read the processes memory while it was owned by root. So if the process held on to its root privileges until later in the flow of control (after the key memory was erased), this bug might not exist (for implementation-specific reasons this may be tricky for the author to do, but in principle there is no reason it can't be).

If the author had done a data-flow analysis of the program (examining program state on entering and leaving the root section of code), this bug probably would have been discovered earlier. But instead he was just "very careful", and released root privs as soon as they were no longer needed to access the critical data. His behavior is perfectly understandable, and generally correct---but in this case, sadly, wrong.

The lesson is not new. Designing secure systems is HARD. It takes a lot of thought, and a lot of examination by security experts before a system can be trusted.

Barry Jaspan,

Re: Floating Point Numbers

Tue, 23 Jan 96 14:32:43 SYD

Hoo! I got a lot of private feedback about my posting regarding floating point number formats! Thank you all of you who did respond and what's more responded in a positive and encouraging way. I went off a little prematurely, so, drawing from the information thrown at me :-) from those replies, I now need to clarify a few things for the readers of RISKS.

My original post was in response to concern of accuracy problems when floating point numbers expressed in decimal are stored in binary. Storage of numbers like 1/3 or 22/7 will continue to be a problem even in decimal (thank you Keith Thompson). But this is a problem we can understand deal with better in decimal than in binary because we humans have been trained to think in decimal numbers from a young age. A radix-10 or radix-100 system only gains you accuracy to exact powers of ten - but that appears to be what people are asking for! (...which was, incidentally, point.)

Microsoft's proprietary format was, it turns out, quite appropriate for what it was designed for (thank you Matthew Healy). Quite simply, they bastardized the IEEE 754 format to make it faster on the CPU technology of the time - which was, remember, sans numeric co-processor. In other words, a classic engineering tradeoff. Since numeric co-processors are now much more common, and CPUs are generally much faster now anyway, Microsoft have gone back to the IEEE format for their software.

But IEEE are very aware of the accuracy problems of IEEE 754 (thank you D. Jason Penney). In fact, they even have a floating point number standard using radix-10 - it is called IEEE 854. The problem is that far too many of the people using *binary* floating point should be using *base-ten* floating point! Part of the reason for this is perception. Binary floating point is presented as the pinnacle of computer number representations - when it is simply "horses for courses". When ray-tracing (for instance), binary floating point is just the ticket. On the other hand, on a financial spreadsheet, base-ten binary is much more suitable - if slower.

It is a decidedly human Risk.


Re: Floating Point Numbers

Wed, 17 Jan 96 16:52:36 SYD

January 96 PC Magazine (Australia) had, not one, but *two* letters in their Tech section relating to "inaccuracies" with floating point numbers. Guess what: *both* times the binary number format was to blame!


Re: RISKS of stolen UN computers (RISKS-17.65)

Dave Scott <>
Tue, 23 Jan 1996 08:16:27 -0600

RISKS-17.65 mentioned the theft from the UN of four computers which held data on human rights violations in Croatia. The risk of not having backups was mentioned, but there are other issues to be considered:

  1. There is definite risk in allowing people to identify the machines or directories on which sensitive data is kept. You might as well hang a "target" sign on it. On our network, for example, I would never establish a directory called "G:\PERSONNEL\PAYROLL\SALARIES" or "G:\MEMOS\REPRIMAND\SEXUAL". There are too many tools available for casual browsing of systems. Hiding the directories may not help; Norton Utilities' File Find, for example, ignores the hidden flag.
  2. I don't know if the UN thought about it or not, but the data files on these machines should have been encrypted, since they probably contain the names of people who informed on human rights violators. These informants should be notified to watch their backs.
I know of a couple of legal offices that have PCs with Syquest or Zip drives; every case has one cartridge devoted to it, and these are removed from the machine and locked in a safe when not needed. Might be a good idea for the UN's rights violation investigators; I really believe that the PCs were stolen not for intrinsic value but for the data.
David M. Scott, CPIM Manager, Systems Services
AMP Packaging Systems, Inc. Round Rock, Texas USA

Cost to crack Netscape Security falls... (RISKS-17.65)

A. Padgett Peterson <>
Mon, 22 Jan 96 21:47:05 -0500

Heck I've been saying for two years now that a special-purpose sieve could break RC4-40 in an average of little over 3 hours. Just a matter of knowing what to use, not CISCs or RISCs but DSPs. (Incidentally, I have seen quite a few people using the 3-hour figure for DES. Maybe with 65k sieves, but not with one.)

Even at 40 Mhz (example above is based on 150 Mhz) you are talking less than 12 hours so what is surprising about several days ?

Add in the fact that RC4 (algorithm was published on sci.crypt last year) is much simpler than say DES, and that breakage via brute force comes reasonably quickly is not surprising to anyone who has studied it, just re-enforces the fact that 40 bit encryption is little better than no encryption at all.

Given the fact that the next generation of game controllers will operate at over 100 Mhz, the real question should be "Who will be the first to break 40-bit Netscape encryption on a Playstation ?"

P.S. Don't blame Netscape, they are just abiding by ITAR.

Re: Single computer breaks 40-bit RC4 in under 8 days

64525) <weimer@ycc.Kodak.COM (Gary Weimer>
Tue, 23 Jan 1996 15:12:56 -0500

I've been amazed from the beginning that people are justifying an encryption algorithm by saying it is "too expensive" to crack. I could crack keys at no cost to myself, and if I'm willing to steal someone's money, I'm certainly not going to be concerned about what it is costing someone else for me to crack keys. At my college I didn't have to pay for CPU time. At my current job, I have access to over 200 Sun Workstations (probably over 300...) on which I could run user processes. I doubt any of them are monitored closely enough to catch an innocently named process that has been niced to avoid hogging the CPU and gets restarted periodically to hide cumulative CPU time. I also doubt that my free access to CPU cycles is all that unusual.

Gary Weimer

Re: Japanese fighter plane shot down another plane

Mickey McInnis <>
Tue, 23 Jan 1996 13:04:32 -0600 (CST)

This seems like a low tech risk hidden mistaken for a high tech risk.

Anyone with any knowledge of weapons knows you never point a loaded weapon at anything you don't intend to shoot even if the "safety" is on. Imagine pointing a loaded handgun at someone an pulling the trigger and saying "It's OK, the safety is on." (As used here, "safety" means "a device that keeps a weapon from firing unintentionally when the trigger is pulled.")

The fact that the F-15 is a multi-million dollar, highly complex system only makes it more necessary to follow basic safety precautions. Whether or not the "safety" failed or the operator misused it, it's a basic mistake to bet a life on the safety.

Actually, it's usually very bad form to point even an UNloaded weapon at someone. Everyone knows there are "ammunition fairies" who put ammunition in unloaded guns when you aren't looking. (OK, maybe there aren't ammunition fairies, but people who believe in them live longer than those who don't. 8-)

Mickey McInnis -

Re: cryo-risks

"Lindsay F. Marshall" <>
Tue, 23 Jan 1996 14:49:40 +0000

People seem to have some misconceptions about how the cryogenics people work. Sure, they have monitoring systems and such like that use electricity, but basically they stick you (or at least your head if you have "gone neuro") inside a big Dewar Flask -- if the power fails no problem for quite some time. Earthquakes are a much worse "risk". For an interesting view of the cryogenics world, read Ed Regis's "Great Mambo Chicken" and the chapter on cryogenics in "Death: The trip of a Lifetime", which is the book of the US Public TV series of the same name. (Both also well worth reading for the other material they contain)

Robots going crazy

Bertrand Meyer <>
Tue, 23 Jan 96 10:57:12 PST

This is probably not new, but the problems can only get worse as our tools get better.

Last Sunday I posted a news message on comp.lang.eiffel. The next day I received an empty e-mail message "Re" my posting. I wrote back to the sender, asking what was wrong, and received the following reply:

> Please accept our apologies. Our new "beta" software for one of our mail
> robots/spiders went a little beserk [sic] today and dumped several thousand
> incorrect email messages.

> The problem is at our end and we do apolgize. [sic]

Apart from the enormous potential for disaster, what I find interesting is the continuous gradation that exists between, at one extreme, behavior that is considered perfectly normal (all kinds of strange beasts foraging everyone's information repositories, without any warning let alone requests for permission, at all hours of the day and night), and, at the other end, activities that can land people in prison (e.g. the Great Internet Worm, whose author has maintained was an innocent experiment gone awry). I don't think anyone can define a theoretical boundary between the acceptable and the reprehensible.

-- Bertrand Meyer ISE EiffelTech, Santa Barbara <>

Re: Hey, your mailing list is sending me viruses!

"Alan K. Jackson 544-4442" <>
Tue, 23 Jan 96 07:47:26 -0600

I have an AOL account, and I think I can explain what happened. AOL has had severe mail server problems lately. The way the AOL mail download works is this :

  1. AOL downloads a TOC for all the mail to come to a binary file
  2. The messages get downloaded into the file
  3. Attachments get downloaded
Because of the mail server problems, the TOC for a message was getting downloaded, without the message itself. To the user, everything looks okay, but when you try to open an empty message, AOL hangs and it is ctl-alt-del time. Sometimes a power cycle is necessary.
Alan K. Jackson, West Africa Team, Geophysical Interpreter, Pecten Internat'l Company, Box 205,Houston,Tx 77001 (713)544-4442

Re: Hey, your mailing list is sending me viruses!

Joe A. Dellinger <>
Mon, 22 Jan 96 19:59:14 CST

It may not be AOL's software at all. It could be in a gateway transmitting packets from AOL to the user, or even in the user's own modem or terminal emulation software.

A few years ago I reported on comp.risks my experiences with a gateway that would hang and need to be rebooted if it saw more than a handful of lines like this one go by:


Since it was the gateway itself causing the problem, ANY attempt to transmit the offending string uncompressed and unencrypted would cause the problem: ftp, e-mail, or merely scrolling the message by as text on your screen!

I'm told some brands of modem will promptly disconnect if they see the string "+++" go by at any point in the data stream.

And surely people remember back in the days before X how much fun it was to send "^[c", the ANSI terminal "reset" sequence, to another user's terminal? This could be done in many ways: you could put it in your ".plan", or e-mail it to them, or simply send it to their screen if you had permissions to do so. On many brands of terminal it would cause the victimized user to be instantly disconnected!

AOL E-mail crashes (Re: RISKS-17.65)

Bostrom <>
23 Jan 1996 11:46:59 -0500

This has been a problem with AOL's e-mail client (the Windoze version, at least) for the last two releases. The problem is quite simple, really. When a user requests to check for new mail using AOL's software, the machine first retrieves a list of mail headers, then (if requested) retrieves the actual body of each mail item. If the client machine loses carrier or is otherwise disconnected during a "flashsession" (batch mail retrieval/delivery) or in the middle of retrieving an individual piece of mail after the list has been retrieved, the software is left with a bodyless header (kind of gruesome, really). Trying to read that piece of mail will then lockup the AOL client software. This is obviously not a virus (unless those jokers at the San Jose Mercury are including virii with their news feeds?).

Deleting the dismembered headers in the locally stored client list of mail headers "fixes" the problem, although that bit of mail is then lost.

Because of work, I've had to suffer with this bug for some time now. AOL's staffers just don't seem to understand the problem, in spite of many and varied attempts to explain. Sometimes I think they only receive and read headers themselves. But how about the spontaneously disappearing >hundreds< of pieces of locally stored mail? That's another story...

Doug Bostrom Atlanta, GA AMNET, Inc.

E-mail spamming risk

Dan Zerkle <>
Mon, 22 Jan 96 17:42:49 PST

"Fred Sterling" is a pseudonym for a charlatan who has been advertising his trash via massive e-mail spams. He has been thrown off of various sites for these activities, and is his latest hideout. He is the cause of the development of e-mail filters, as his junk mail was causing problems for high-cost international UUCP and FIDO connections.

The risk? Only the usual tragedy of the commons (unless you count the embarrassment of a certain moderator). See for further details.

"Learning Machines" and "Learning People" (Beware of "Fred Sterling")

"Peter G. Neumann" <>
Tue, 23 Jan 96 8:12:05 PST

Thanks to an unprecedented number of you for your comments noting that RISKS got spammed. I generally make a very serious effort to reject all overt advertisements, spams, and sneaky attempts to abuse the Internet. In particular, the moderator of a group dedicated to risks in the use of computers must never let his attention span wander, not even for a moment. But, somehow, that item slipped into RISKS-17.65. (The worst part is that I surprisingly forgot about Rob Slade's VERY EXPLICIT WARNING about "Fred Sterling" in RISKS-17.54 ["Pick a personality type, any personality type ..."] and also that I did not even try the dratted website -- which I usually do before even considering posting anything like that. That certainly would have jarred my memory and my sensibilities.) [Yes, Dan, I am indeed embarrassed!]

This is just one more reminder of the risks in the open Internet and is a harbinger of the problems we will increasingly be having. Also, don't forget the risks of security problems (especially Trojan horses) in the network interfaces. I'm waiting for the first really successful sucker punch, which will undoubtedly lead to draconian legislative restrictions, which will in turn lead to more discussions on this topic in RISKS.

At any rate, I appreciate the messages from all of you who objected to its inclusion. In response, I have done something rather unusual -- removing the offending item from the archive copy of RISKS-17.65. (Other archivists may feel free to pick up the new copy if they wish to follow suit.) Especially in the light of my having let through an obviously unworthy contribution, I also must apologize to those of you who have submitted truly worthy messages that have not (yet) made it into RISKS. The volume of submissions has been enormous lately, and I have a particularly tricky task of selecting what I hope will be most interesting for you, from among a very large queueueueueueueue, while not incurring the wrath of others for including junk. Always feel free to poke me if you feel I have ignored a particularly vital contribution of yours (even though that will further increase the volume I must deal with!). Many thanks for your patience. PGN

"Learning machine" spam (RISKS-17.65)

Martin Kealey <[address-deleted-as-requested]>
Wed, 24 Jan 1996 07:51:35 +1200 (NZST)

In the light of this subject matter, I'd ask for my electronic address not to appear in plaintext in this message, although to solicit genuine replies I am including enough information to construct it.

I'm rather disappointed to see this blatant advertising spam reproduced here; despite the "If you wish to be removed" line, they've simply dredged the net for as many e-mail addresses as they can; I know dozens of people who've received this message, so it seems they have been mailing every address they can find - including some of my private addresses that have never been used to make newspostings.

As far as I'm concerned, an offer to be removed is better than nothing, but the underlying "mail to everyone in the world" approach is still so obnoxious as to outweigh this token; after all, there are enough potential advertisers in the world to completely swamp our mailboxes with even one message each.

The risks?

  1. Our esteemed moderator seeing what seems to be a honest testimonial and publishing it as "an interesting item";
  2. The risk to society when people don't get educated about or just ignore "social harmony" rules. Just because it won't be a terrible thing if one person does something doesn't mean that everyone should be allowed to do it - the combined effect if multiplied a million-fold (or more) could be less than desirable.
  3. For the ignorant (or the recidivist), the relatively low effort required to annoy vast numbers of people means that this is going to become all too common.
I'm working on an idea that I hope will increase the cost of advertising by requiring manual intervention for each separate recipient, while not stopping messages from valid senders.

The basic idea is to keep a list of authorised senders (patterns for generality) whose messages will go straight through as normal. Other messages get "locked" in a holding queue, after they are auto-replied with instructions on how to unlock them. This would entail sending a one-off key in a manner that will require some simple operation performed on it as described by accompanying text. Any message not unlocked within say 2 days will be deleted.

Before I put in a great deal of effort into implementing it, does anyone see any risks I have missed? Would you be upset to get back a message like this:

Sender: (Advertisement Blocker)
From: (Martin Kealey)
To: (Your Name)
Subject: Re: previous subject line

Your message <> has been locked in a holding queue pending delivery to (Martin Kealey) because has not previously been encountered by this system. Instructions for unlocking it to allow delivery follow.


This is not to say that merely being disagreeable will lead to these consequences, but it might not get you permanently approved either.

If you wish to unlock your message, please send a message with "unlock.87326482376" in the subject header to; otherwise this message will be deleted in 48 hours. If your message is in good taste, and not trying to waste my time, then you will be added to the list of approved senders.

This filter is freely available software; its purpose is to reduce unsolicited advertising by reducing its cost- effectiveness; please use it and encourage all your friends to use it too.

- AdCheck v0.0, on behalf of Martin Kealey

Some risks that I can see:

  1. failing to enable the bypass on a return message when sending a new message could result in two instances of this program talking to each other;
  2. attempting to overcome the above in any simple-minded manner (eg, accept all mail from adcheck@*) could result in a loophole that would enable spammers to discredit the system; - Someone might have trade-marked AntiSpam somewhere.
If anyone has any ideas, please send me mail at site (any of the obvious usernames will work). If I catch anyone putting that address into a commercial mailing list of any sort, I'll personally string you up by your ears!
- Martin Kealey

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