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 9 Issue 58

Tuesday 9 January 1990


o New-Years' Lotto goes Blotto
Jim Anderson
o Railroad interlocking systems
Douglas W. Jones
o Sorry, the bank's already debited your mortgage
Dave Horsfall
o Positive fingerprint identification?
Dave Horsfall
o Re: Password Security: A Case History
Fernando J. Corbato
o The risks of not learning - and of ignoring realities
Jerry Leichter
o 6th Chaos Communication Congress, Hamburg 27-29 Dec 1989
Klaus Brunnstein
o Info on RISKS (comp.risks)

New-Years' Lotto goes Blotto

"Peter G. Neumann" <>
Mon, 8 Jan 1990 11:40:31 PST
The Pennsylvania Wild Card Lotto computer systems had to be reprogrammed to
accommodate the end of the decade.  That had already supposedly been
accomplished -- but apparently not carefully enough.  In the first Lotto of
the new decade, the computer systems were unable to determine the winners and
further software fixes were required.  [Philadephia Inquirer, 4 Jan 1990,
contributed by James P. Anderson]

Railroad interlocking systems

Douglas W. Jones <>
Fri, 5 Jan 90 09:49:21 CST
Most of the arguments about safety critical hardware and software that I've
seen assume that digital computers pose new problems.  In effect, the
argument is that safety critical digital control systems are a radical
novelty (to borrow from Dijkstra's essay on the Cruelty of Teaching Computer
Programming), and thus that they cannot be discussed by analogy to older
solutions to the same problem.

One historical parallel which may prove interesting in this context is the
railroad interlocking machine.  Interlocking machines were purely mechanical
digital computing machines that served to enforce a set of operating rules on
railroad signalmen operating the switch-tracks and signals at a railroad

I suspect that there are useful parallels between the history of railroad
interlocking machines and the more recent developments in safety critical
digital control systems.  An error in the logical design of an interlocking
machine could easily go undetected until it caused a train wreck, and I
wonder if old cases involving railroad interlocking machines might provide
useful precidents for many of the software liability questions that have been
raised recently.

Here's a short description of the problem solved by a relatively
simple interlocking machine:

   Consider the following track layout:

                       3->     TOWER                  8->
           <-1    \                      <-5    /
                   \   4->                     /

       1, 5 and 6 are signals controlling traffic from the left.
       3, 4 and 8 are signals controlling traffic from the right.
       2 and 7 are switch tracks.
       All signals may be up (go) or down (stop).
       All switch tracks may be set to direct traffic up to the
         straight through track or down to the siding.

       The control levers for all of the signals and the switch
         tracks are located in the tower, where the signalman may
         work them one at a time.  (One at a time because it takes
         his full strength to overcome the friction of the system
         of cranks and push-rods that connects each lever to the
         corresponding switch-track or signal.)

   The problem:  There are 8 levers in a row, each with 2 settings;
     thus, there are 256 possible states of the system.  (I've seen
     photos of old railroad control towers with banks of 20 or more
     control levers.)  Of these 256 states, only a few are safe.

       Example:  If switch 2 is set up, switch 7 is set down, and
         signals 1, 4, 5, and 8 are up, a train entering the
         diagram from either side will procede through the diagram
         and derail as it passes through the incorrectly sew switch
         at the opposite side of the diagram.

   The classic solution:  A mechanical interlocking machine is added
     to the tower.  A tower containing an interlocking machine was
     a sufficient improvement over an un-interlocked control tower
     that the term interlocking tower came to be applied to such a
     tower.  An interlocking machine consists of a set of 8 transverse
     rods crossing 8 rods linked to the control levers.  Each transverse
     rod is linked to one of the control rods and at each point where
     a transverse rod and a control rod cross, the transverse rod may
     be notched to allow the control rod to move or un-notched to lock
     the setting of the control rod.

       In the above example, signals 1, 3 and 4 would be interlocked
         with switch track 2 such that the setting of 2 could only be
         changed if 1, 3 and 4 were in the down position, and so that
         3 could only be raised to the up position if switch 2 was
         set up, and 4 could only be raised to the up position if
         switch 2 was set down.  A similar set of interlocking rules
         would apply to 5, 6, 7 and 8.

     The "program" for the interlocking machine can be viewed as the
     pattern of notches in the transverse rods.

Modern solutions to the interlocking problem use electrically operated
switches and signals with relays and more recently computerized controls to
interlock their operation.  Long before such modern solutions came into use,
interlocking machines were built into the control towers along most mainline
trackage in North America.  The interlocking machines for simple passing
sidings such as I've described above could be standardized, but there were
(and are) many places where the track layout controlled by an interlocking
tower was unique and required what we would now call custom programming.

Incidentally, in addition to the possible relevance of the history of
interlocking towers to modern problems in safety-critical computing systems,
lots of good assignments can be derived from this problem.  For example,
given a set of interlocking rules, derive a finite-state machine describing
the legal states transitions.  Alternately, write a program that, when given
the current state and a (partial?) specification of a desired state, produces
a plan for a series of legal transitions that will reach the desired state.

Douglas Jones, Dept. of Computer Science, Univ. of Iowa, Iowa City, Iowa, 52242

Sorry, the bank's already debited your mortgage

Dave Horsfall <>
Sat, 6 Jan 90 22:49:18 est
In the wake of sky-rocketing mortgage rates in Australia comes this
story from the "Sydney Morning Herald", Friday January 5th, 1990:

``Sorry, the bank's already debited your mortgage

  As many as 100,000 Commonwealth Bank customers found their accounts
  prematurely depleted yesterday when a computer debited home loan
  payments due for any day in January rather than just Wednesday.

  The Commonwealth's general manager, retail, Mr Peter Andrews, said
  staff became aware of the mistake when some customers found cheque or
  Keycard accounts debited ahead of time.

  Mr Andrews said a computer sweep on Tuesday night would normally have
  debited customers who had elected to pay their home loans automatically
  on Wednesday.

  The error affected up to 100,000 home loan holders throughout Australia,
  but Mr Andrews said most customers would not have become aware of it.
  They would have noticed "only if they were taking money out and found
  their accounts were overdrawn," he said.  Emergency arrangements had
  been set up to give them access to cash.''

Dave Horsfall (VK2KFU),  Alcatel STC Australia,,  ...munnari!!dave

Positive fingerprint identification?

Dave Horsfall <>
Mon, 8 Jan 90 19:28:21 est
The following is taken from "The Sydney Morning Herald" Mon 8th January:

``Positive identification

  It might not have caught the killer, but at least it has identified
  the victim.  A fingerprint checking computer immediately revealed to
  Seattle police the identity of a body found along a busy road in
  Portland.  A manual fingerprint comparison, using the police
  department's hundreds of thousands of fingerprint files, would have
  taken months, according to police.  The computer's _positive
  identification_ [ emphasis mine ] took just a few seconds.''

Dave Horsfall (VK2KFU),  Alcatel STC Australia,,  ...munnari!!dave

Re: Password Security: A Case History

"Fernando J. Corbato" <corbato@LCS.MIT.EDU>
Mon, 8 Jan 1990 18:02:43 EST
Peter's note recalling the colossal time-sharing mishap of the interchange of
the message-of-the-day with the password file which occurred on CTSS in the
early 1960's made me go look up the article and see what was said about the
cause.  The article says "due to a software design error, the temporary editor
files of the two users were interchanged..." but it was deeper than that.

To simplify the organization of the initial CTSS system, a design decision had
been made to have each user at a terminal associated with his own directory of
files.  Moreover the system itself was organized as a kind of quasi user with
its own directory which included a large number of supporting applications and
files including the message-of-the day and the password file.  So far, so good.
Normally a single system programmer could login to the system directory and
make any necessary changes.  But the number of system programmers had grown to
about a dozen in number, and, further, the system by then was being operated
almost continuously so that the need to do live maintenance of the system files
became essential.  Not surprisingly, the system programmers saw the
one-user-to-a-directory restriction as a big bottleneck for them.  They
thereupon proceeded to cajole me into letting the system directory be an
exception "since system programmer's would be careful to not make mistakes."

But of course a mistake was made.  Overlooked was that a software design
decision had been made in the standard system text editor that it would only be
used by one user at a time working in one directory so that a temporary file
could have the same name for all instantiations of the editor.  And with two
system programmers editing at the same time in the system directory, the
disaster of the swapped temporary files finally occurred.

The tale has at least two morals: First, design bugs are often subtle and occur
by evolution with early assumptions being forgotten as new features or uses are
added to systems; Second, even system programmers make mistakes so that prudent
system management must be based on expecting errors and not on perfection.

F. J. Corbato

  [For our younger readers, Corby was the father of both CTSS and Multics. PGN]

The risks of not learning - and of ignoring realities

Fri, 5 Jan 90 12:45 EST
In a recent RISKS, Al Arsenault records his distress at an answer he received
on a test he gave in a course on computer security.  A student stated that one
advantage of passwords over biometric authentication was that he could give his
password to a friend so that the friend could use his account.  Mr. Arsenault
comments, "So much for that one-week unit on 'Individual Accountability'".

I'm afraid he is missing an important point.  The fact of the matter is, people
lend things to friends.  They lend clothes, they lend cars, they lend money.
They let people use their telephones.  They even lend things like ID cards when
they can get away with it.  Those in charge of things like security cards don't
like this, and they try hard to prevent it, resulting in a continuous battle
with people who just want to continue to live their lives.

At times, it's easy to forget that most people share neither the world view
nor the interests of the "security community".  Yes, they are aware that they
should not let "anyone" know their bank card password - but when, for example,
they are sick in bed they consider it a useful thing that they can give the
card and password to a friend and have him get some money and do a bit of
shopping for them.  This, too, is a positive good.

I'm sure Mr. Arsenault covered the standard set of distinctions among
identification schemes - something you KNOW, something you HAVE, something you
ARE.  Each has its own features, which in different contexts may be good or
bad.  Something you KNOW can be replicated to others; something you HAVE can be
lent; something you ARE can't be transfered.  These are neither advantages nor
disadvantages; they are simply inherent features.

Consider an analogy: Why is letting someone use your computer account
inherently different from letting someone use your telephone?  Would you never
be willing to tell a trusted friend your telephone access code?
                                    -- Jerry

   [Yes, some people are concerned about computer security and others are not
   -- at least not until they've been burned.  But Reality and Sensibility
  are in this case two radically different things.  If you want individual
  accountability, you do not share passwords.  The telephone system is
  intrinsically vulnerable to illicit use of credit cards.  If you wish to
  trust a friend, that may have low risk -- unless MANY people are involved;
  then you might like to have records that show who is actually using your
  resources.  However, suppose you are designing a computer system that
  recognizes fingerprints as authenticators.  It would be rather silly to
  design the system to recognize facsimile copies of a fingerprint so that
  someone else could conveniently enter the system when provided with a
  fingercopy (which can itself be repeatedly copied).  (Ignore the fact that
  the previous person's fingerprint may be liftable from the glass!)  Much more
  sensible is to design the computer system so that it encourages individual
  accountability, while also permitting flexible controlled sharing.  That is
  what Multics was all about in 1965.  What's new?  PGN]

6th Chaos Communication Congress, Hamburg 27-29 Dec 1989

Klaus Brunnstein <>
05 Jan 90 14:41 GMT+0100
             6th Chaos Communication Congress 1989
               'Open frontiers: CoComed together'

The 6th annual congress of Hamburg's Chaos Computer Club (CCC) was held on
27-29 December 1989 in Hamburg. The recent political development in Germany
also influences the hacker scene; only after a controversial debate, the
organisers denied a suggestion to move the congress to East Berlin. Among the
about 300 visitors, about 50 people from East Germany were present.  A few
foreign visitors came from France, Netherlands and USA. The congress was
male-dominated, with a growing female participation (about 40). The other major
German hacker groups (from Bavaria, Cologne) were not present.

Following trends of the 5th CCC congress, themes relating to computer security
were less dominant. As CCC members and congress organisers age and their
professional background dominates (a significant part works in computing), the
political impact of computerisation becomes dominant, not only under a revised
West/East German scenario. Even the presentation of changes:
invited speakers with solid scientific background lecture in traditional style,
some even with overhead folios from international conferences; even a state
attorney (responsible for the case FRG vs.S. Wernery re hacking!) participated
in a surprisingly fair and open discussion on criminal law against hacking.

Major themes were:
      - information about computerisation and network infrastructure
        in East Germany
      - cooperation with East German computer freaks
      - cooperation with eco-groups
      - 'female computer handling'
      - KGB-hacker 'Hagbard'
      - Security in open networks (2 invited speakers)
      - Hacker Ethics and Harper's Hacker Conference (Capt.Crunch)
      - Free Flow of Information, Copyright
      - UNIX discussions: several workshops, UUCP
      - Virus Forum II.

Several sessions were devoted to the state and possible developments of
computers + communication (c+c) in East Germany. With insufficient computers
and an outmoded telephone net, CCC appealed to the German public to donate
unused equipment (C64, Apple II, PCs) to eastern groups. As substitute of the
insufficient telephone net, the recently installed 'packet radio' should be
used for computer communication; pc-communication with packer-radio was
demonstrated at the exhibition. As a start of computerisation, CCC plans to
hold another congress (Kaos Kommunikation Kongress) in East Berlin early in

Representatives of the East German citizen movement, esp.from 'New Forum'
discussed possible developments. Many participants (most oriented towards the
left wing of the political spectrum) adviced the East Germans not willingly to
follow West German c+c industry and public authorities (Telekom) to install
traditional technology; as an example, ISDN is widely critized because it
neglects data protection laws.

Following discussions on CCC congress 88, several projects of ecological data
processing and communication started (e.g. data collection in the environment
of industry and nuclear power plants). CCC and some eco-groups plan to install
an information center on a ship during the EEC's North Sea conference (March
1990). A special session and workshop was also devoted to female
computer-handling; a goup of male (30) and female (20) participants discussed
the role and attitudes of women in education and profession; similar
discussions in national and international conferences (e.g. IFIP TC-9) may
point to revised design principles (e.g. reduced complexity, possble
plausibility control).

Only a minor part of the congress was devoted to traditional hacker themes.
Surprisingly, CCC did not follow it's tradition to extensively discuss hacker
experiences of the last year. The KGB hack (broadly published in March, 1989)
was *no theme*; instead, a session was devoted to the memory of Karl Koch alias
'Captain Hagbard', one of Cliff Stoll's 'Wily Hackers' (CACM 5/1988) who, after
having informed the public authorities as one of 2 chief witnesses in the case,
committed suicide. 3 personal friends (without any interest in computing) and
PENGO (the other chief witness) described Hagbard's sad life story, full of
family problems and addictions (drug, hacking). The role of the media as well
as CCC's role (part of which had strongly denied any contact to the crackers)
was controversially discussed.

Btw: the trial against 3 KGB hackers will begin on January 11,1990.

A whole 4 hour session was devoted to 'Security in open networks', with Dr.
Raubold (director in GMD, the national research institute for computers and
communication) and Dr. Pfitzmann (Karlsruhe, Faculty for Informatics)
introducing into technologies of encryption (DES, RSA) and of secure
communication in open networks; the 20 participants which stayed until the end
were mainly students of Informatics and programmers.

'Captain Crunch' reported about the recent electronic conference which was
sponsered by Harper's; the results will be published in this magazine early in
1990 (survey document in English available on request). He moreover
demonstrated, via AT+T operator swithced connection, PicturePhone.

Virus Forum II (1989) was intended to show the developments since Forum I
(1985) where CCC made viruses publicly known in FRG. Ralf Burger (author of a
Virus Book, where he published also virus code including a MVS/370 virus), Wau
Holland (CCC's founding father), Juergen Wieckmann (editor of Chaos Computer
Book) and K.Brunnstein discussed trends of viruses.  Meanwhile, more than 80
viruses are known on INTEL 80xxx-systems, and more than 70 on several
68.000-systems as AMIGA, Atari and MacIntosh. Viruses are found to grow from
'families', the descendants of which are ever more difficult to analyse and
produce growing damages.

While the participants agreed in the threat assessment, there was significant
disagreement about the consequences. Burger argued that everybody can program a
virus; publication of virus code does not contribute to the virus threat.
Brunnstein argued strongly against, that many young programmers learn to
program viruses mainly from published code which they change slightly to
produce their own virus; even if they program a virus for learning purposes,
they loose control when it spreads via the friends' diskettes. Virus
publication as part of virus distribution presents severe threats to data
processing in economy, public services and private life.  IFIP General Assembly
therefore passed a motion that every member society should appeal to its
national legislative bodies to classify virus publication and distribution as a
crime (the author will send the text of the IFIP resolution on request:
VIRUSBAN.DOC: 56 lines, 3 kBytes).

Another controversy raised when Burger told the audience: 'My antivirus finds
every virus'; unfortunately, he didnot accept a bet from the audience to prove
his promise. Burger also said, that he needs only one hour to detect and
eliminate any anomaly; this differed significantly from the 250 hours which
according to Brunnstein are needed to analyse and classify a complex virus and
to produce the proper antivirus.

Some participants from the audience differentiated between good use of viruses
and bad use. It could be Good Use of viruses against inacceptable activities,
such as nuclear weapons or state activities such as census.  Following such
ideas, Wau Holland said that the existence of viruses gives a chance to analyse
whether they are 'socially acceptable'.

The `electronic newspaper', which reports the major discussions of CCC'89, was
significantly more professionally organised than last year; it was produced by
the team of CHALISTI, CCC's newly (1989) founded electronic newspaper, as
edition no.4. Due to the minor foreign participation, most documents are
German, with only two documents are written in English (Capt.Crunch's report on
the Harper Hacker Conference, and the IFIP General Assembly's resolution on
legal activities against viruses). There may be an English translation of the
CCC newspaper in some time (?early February); I will send a short notice to PGN
when this is available.  People interested in the German version (1794 Lines,97
kBytes) or the English documents (135Li nes,8 kBytes) can reqzuest it from the

Conclusion: CCC and its constituency is on the *way to professionalism*.  On
this way, CCC may loose control and even contact to real hacker groups, which
they previoulsy hold in cases such as Btx and NASA hack; in the KGB case, CCC
evidently had neither information nor control of the crackers.  On the other
hand, CCC's propagation of UNIX enlarges the threats inherent in UUCP and the

Klaus Brunnstein       University of Hamburg, FRG    January 3, 1990

Please report problems with the web pages to the maintainer