The RISKS Digest
Volume 8 Issue 74

Friday, 26th May 1989

Forum on Risks to the Public in Computers and Related Systems

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

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o Aegis, Vincennes, and the Iranian Airbus
PGN interpreting Matt Jaffe
o Anti-lock brake system failure - fail-safe?
Jay Elinsky
o Pleasure boat database helps thieves
Howard Gayle
Les Earnest
o SABRE disaster caused by "core corruption"
Andrew Birner
o Computer Intrusion Network in Detroit
Dave Curry
o Robert T. Morris suspended from Cornell
Dave Curry
o Info on RISKS (comp.risks)

Aegis, Vincennes, and the Iranian Airbus (report on a Matt Jaffe talk)

Peter Neumann <>
Fri, 26 May 1989 13:44:01 PDT
In a keynote talk for the 5th International Workshop on Software
Specification and Design in Pittsburgh, 20-21 May 1989, I cited the case of
the Aegis' role in the Vincennes' shootdown of an Iranian Airbus as an
example of a system in which the design of the user interface was critical.

Matt Jaffe ( responded with some comments on the Aegis user
interface — in whose design he had played a part while at RCA — after which
he was invited to gave an impromptu talk on his experience to the workshop.

As you may recall, the Iranian Airbus was shot down by the Vincennes, although
it was on schedule, on course, and apparently flying completely normally.
There was confusion between the commercial plane being tracked and an observed
IFF (Identification, Friend or Foe) squawk from a fighter plane.  The altitude
information (Z) was not displayed on the main screens, but only in one of
various subtables that had to be called up on a smaller screen.  There was no
indication of rate of change of altitude (Z', or "Z-dot"), not even a ternary
choice among ascending, cruising, or descending.  Matt took the view that the
user interface could not have done much differently, because of intrinsic
limitations on

  1. the reliability and/or accuracy of the underlying data, 
  2. the physical and logical characteristics of the display devices
     (alphanumeric raster-scan screens with limited space)
  3. and the ability of human operators to interpret marginal
     data in the high volume and high stress environment.

This is an attempt to summarize Matt's main points:

  Mode II codes (military use only) cannot be conclusive in determining friend
  or foe because they can be spoofed by a non-friendly aircraft, as can the
  civilian use Modes I and III.  In this particular case, the military
  aircraft supplied by the US to Iran almost certainly included Mode II
  transponders.  Note some subtle points here.  IFF is to determine the
  identity of friendly aircraft, not the military capability of a non-friend.
  In this tragedy, the problem was not in discriminating between friends and
  all others but between an Iranian F-14 and an Iranian airliner.  The
  identification as Iranian was correct (and presumably not based on IFF but on
  point of origin).  A classification of a Mode II code as belonging to an
  Iranian military aircraft would seem reasonable given that the airfield from
  which the aircraft departed was a joint use airport (both civilian and
  military).  What may have happened was that the airliner taxied near enough
  to an F-14 on the ground as to preclude the system from recognizing that
  there were in fact TWO aircraft.  (ANY sensor has some resolution limits.)
  Once the airliner was airborne, its lack of further mode II activity would
  not preclude the display of the old Mode II code.  Aircraft may fail to
  respond to an IFF interrogation (of any code) for a variety of reasons and
  yet operators (both civil and military) want to have the last recieved code
  remain displayed.

  Thus the entire mechanism contains potential ambiguities.  Providing a
  recency field for Mode II squawks would probably have been a good idea,
  display space and operator cognitive limits permitting.  (At that time and
  to date, Matt indicated that he knew of no system that provided the age of
  last squawk; nor did the Navy mention the possibility.  Scary?)

  The altitude readings are generally unreliable.  Thus, the Z' calculations --
  irrespective of how they were done — would be suspect, and subject to
  possible misinterpretation.  Nevertheless, some crude up-down-same field
  might have been useful.

  Uncertain or unreliable information will always be a major problem in any
  safety-critical system.

  From the Navy's point of view, the Captain of the Vincennes did the right
  thing — based on what he knew.

  No standard Navy shipborad systems could have done the discrimination
  automatically.  No equipment necessary for the Vincennes mission could have
  prevented a manual decision from being difficult, nerve-wracking, and

  The situation was basically untenable in the first place, with hostile
  aircraft and commercial airliners closely interwoven within an area of great

  [The Stark Captain had said earlier that they had not realized the
  limitations of the combat system in that kind of an environment.  PGN]

Matt made the appropriate disclaimers — that his knowledge is not current,
that his opinions were his own, etc.  And his audience was generally impressed
with the care with which he had thought out the issues.  All in all, this case
is of great importance, and bears close consideration.  There are many lessons
to be learned, some technological and some nontechnological — many of the
latter relating to the intrinsic limitations of trusting the technology,
especially under adverse circumstances.  PGN

Anti-lock brake system failure - fail-safe?

Thu, 25 May 89 07:40:57 EDT
The June 1989 issue of Consumer Reports includes a test of the Chevrolet S-10,
as well as three other sport/utility vehicles.  The Chevrolet has rear-wheel
anti-lock brakes.  This is from the "Reliability" section of the report on the

  "The most disquieting [sample defect] was a defective antilock brake
  controller.  At just over 200 miles, the brake warning light came on and the
  pedal sank almost to the floor.  The pedal felt spongy and sank slowly during
  each brake application.  The controller was replaced under the warranty."

I would have expected that a controller failure would leave you with normal
brakes, and perhaps a warning light glaring at you to warn that the brakes are
now manually controlled.  Instead the failure mode sounds like a plain old
brake system leak, except that Consumer Reports didn't say that braking power
was actually lost.  Was there braking power left only because the front brakes,
which I understand do most of the braking, weren't controlled by the defective
controller?  In any event, finding the brake pedal much lower than you expect
it to be, is a risk in itself.

It's also interesting that Consumer Reports didn't make a big deal out of
this problem, so perhaps they don't consider it to be a major risk.

Jay Elinsky, IBM T.J. Watson Research Center, Yorktown Heights, NY

Pleasure boat database helps thieves

Howard Gayle <>
Wed, 24 May 89 14:02:07 +0200
This is based on an article in the Stockholm newspaper Dagens Nyheter, 24 May
1989, p.6.  Last year, a law went into effect in Sweden requiring the
registration of most pleasure boats.  The database is financed by a small "user
fee," i.e., a tax.  The data are public information.  A thief who steals a boat
can phone the registration office, tell them the boat's registration number,
and obtain the legal owner's name, address, and national ID number.  This makes
it easy for the thief to impersonate the legal owner when selling the stolen


Les Earnest <LES@SAIL.Stanford.EDU>
23 May 89 0131 PDT
This is an account of two ancient (30-year old) computer risks that were
not publicly disclosed for the usual reasons.  It involves an air defense
system called SAGE and a ground-to-air missile called BOMARC.

SAGE was developed by MIT in the late '50s with Air Force sponsorship to
counter the threat of a manned bomber attack by you-know-who.  It was also
designed to counter the political threat of a competing system called Nike
that was being developed by the Army.

SAGE was the first large real time computer system.  "Large" was certainly
the operative term — it had a duplexed vacuum tube computer that covered
an area about the size of a football field and a comparably sized air
conditioning system to take away the enormous heat load.  It used an
advanced memory technology that had just been invented, namely magnetic
core, and had a larger main memory than any earlier computers, though it
is not impessive by current standards — it would now be called 256k
bytes, though no one had heard of a byte then.

The system collected digitized radar information from multiple sites and
used it to automatically track aircraft and guide interceptors.  SAGE was
designed to work initially with manned interceptors such as the F-102,
F-104, and F-106 and used a radio datalink to transmit guidance commands
to these aircraft.  It was later modified to work with the BOMARC missile.

Each computer site had about 50 display consoles that allowed the
operators to assign weapons to targets and monitor progress.  As I recall,
there were eventually between one and two dozen SAGE systems built in
various parts of the U.S.

BOMARC missiles used a rocket booster to get airborne and a ramjet to
cruise at high altitude to the vicinity of its target.  It was then used
its doppler radar to locate the target more accurately so that it could
dive at it and detonate.  It could carry either a high explosive or a
nuclear warhead.

BOMARCs were housed in hardened structures.  When a given missile received a
launch command from SAGE, sent via land lines, the roof would roll back, the
missile would erect, and if it had received a complete set of initial guidance
commands in the meantime it would launch in the specified direction.

            Testing the fire-up decoder

It was clearly important to ensure that the electronic guidance system in the
missile was working properly, so the Boeing engineers who designed the launch
control system included a test feature that would generate a set of synthetic
launch commands so that the missile electronics could be monitored for correct
operation.  When in test mode, of course, the normal sequence of erecting and
launching the missile was suppressed.

I worked on SAGE during 1956-60 and one of our responsibilities was to
integrate BOMARC into that system.  This led us to review the handling of
launch commands in various parts of the system.  In the course of this
review, one of our engineers noticed a rather serious defect — if the
launch command system was tested, the missile would be in a state of
readiness for launch.  If the "test" switch was then returned to "operate"
without individually resetting the control systems in each missile that had
been tested, they would all immediately erect and launch!

Needless to say, that "feature" was modified rather soon after we mentioned it
to Boeing.

            Duplexed for reliability

For some reason, I got assigned the responsibility for securing approval to put
nuclear warheads on the second-generation BOMARCs, which involved "proving" to
a government board that the probability of accidentally launching a missile on
any given day as a result of equipment malfunctions was less than a certain
very small number and that one berserk person couldn't do it by himself.  We
did eventually convince them that it was adequately safe, but in the course of
our studies we uncovered a scary problem.

The SAGE system used land lines to transmit launch commands to the missile site
and these lines were duplexed for reliability.  Each of the two lines followed
a different geographic route so that they would be less likely to be taken out
by a single blast or malfunction.  There was a black box at the missile site
that could detect when the primary line went bad and automatically switched to
the alternate.  On examination, we discovered that if both lines were bad at
the same time, the system would remain connected to the alternate line and the
amplifiers would then pick up and amplify whatever noise was there and
interpret it as a stream of random bits.

We then did a Markov analysis to determine the expected time that it would take
for a random bit stream to generate something that looked like a "fire" command
for one of the missiles.  We found that expected value was a little over 2
minutes.  When such a command was received, of course, the missile would erect
and prepare to launch.  However, unless the missile also received a number of
other commands during the launch window, it would automatically abort.
Fortunately, we were able to show that getting a complete set of acceptable
guidance commands within this time was extremely improbable, so this failure
mode did not present a nuclear safety threat.

The official name of the first BOMARC model was IM-99A, so I wrote a report
about this problem titled "Inadvertent erection of the IM-99A."  While that
title raised a few eyebrows, the report was destined to get even more attention
than I expected.  Its prediction came true a couple of weeks after it was
released — both phone lines went bad on a BOMARC site in Maryland, near
Washington D.C., causing a missi

SABRE disaster caused by "core corruption"

Wed, 24 May 89 18:08 PDT
 According to an article by Margie Semilof, entitled "SABRE Recovers from
Network Crash", in Communications Week, May 22, 1989, the recent SABRE outage
occurred when the "Online DASD formatter was changed erroneously by another
software program operating at the same time.  This 'core corruption' resulted
in the destruction of critical system data on SABRE's 1,800 DASDs."
 The article later quotes Jim Juracek, vice president of systems engineering
for SABRE Computer Services:

     "All the predictable things are covered," Juracek said.  "The unpredict-
     able things, such as when a software program gets clobbered by another
     program . . . [ellipsis hers] there is no way to work with this."

 The article further notes that "SABRE is developing software that will
provide memory protection of applications, and thereby help prevent against
core corruption.  That software will not be ready[,] however, until the early
to mid 1990s".

 Using software for memory protection?  In the 1990s?  How, I wonder, will
they protect their protection software ("quis custodiet ipsos custodes", as
always)?  Is SABRE is too tightly coupled to its hardware to be moved to a
platform that provides hardware memory protection?  Or is it just plain too
big to be ported?

Andrew E. Birner — Zenith Electronics Corp — Zenith/

Computer Intrusion Network in Detroit

Thu, 25 May 89 19:01:31 -0700
Taken from the San Jose Mercury News, 5/25/89 (Knight-Ridder News Service).

  DETROIT - Secret Serviceagents smashed what they described as a costly,
sophisticated computer intrusion network Wednesday and were surprised to
discover it made up largely of teen-agers.
  The computer systems of more than 20 companies including the Michigan
Department of Treasury and Home Box Office cable television services, were
infiltrated, according to agents serving search warrants across the country.
  Federal officials said the infiltrations by the network represented fraud
of $200,000 to $1.5 million in appropriated goods, telephone and computer time.
  Agents expected to arrest some adults when they swept down on eight people
who allegedly ran the network in several states.  Instead, they found only
one adult, in Chicago.  The rest were teen-agers as young as 14: two in
Columbus, Ohio; two in Boston; two in Sterling Heights, Mich.; and one in
Atlanta.  Agents expected to make another arrest in Los Angeles.
  Officials said at least 55 other people nationwide made use of the
network's information.
  In Sterling Heights, Secret Service agents pulled two eighth-grader boys,
both 14, out of school and questioned them in the presence of their parents,
who apparently were unaware of their activities.  James Huse, special agent in
charge of the U.S. Secret Service office in Detroit, said the youths admitted
involvement in the scheme.
  He said the eight-graders [sic], because they are juveniles, cannot be
charged under federal law and will be dealt with by local juvenile
  Authorities believe the mastermind is Lynn Doucett, 35, of Chicago.  She
was arrested Wednesday and is cooperating with authorities, Huse said.
  Doucett, who was convicted in Canada of telecommunications fraud, supports
herself and two children through her computer intrusion activities, which
include using stolen or couterfeit credit cards for cash advances or money
orders, according to an affidavit filed in U.S. District Court.
  If convicted, she faces up to 10 years in prison and a $250,000 fine.

Robert T. Morris suspended from Cornell

Thu, 25 May 89 18:49:38 -0700
Taken from San Jose Mercury News, 5/25/89 (From the New York Times)

  Cornell University has suspended the graduate student identified by school
officials as the author of [the Internet worm].
  In a May 16 letter to Robert Tappan Moris, 23, the dean of the Cornell Uni-
versity Graduate School said a university panel had found him guilty of vio-
lating the school's Code of Academic Integrity.
  He will be suspended until the beginning of the fall semester of 1990, and
then could reapply.
  No criminal charges have been filed against Morris.  A federal grand jury
this year forwarded its recommendations to the Justice Department, which has
not taken any action.    [....]

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