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 15 Issue 73

Friday 1 April 1994


o A320 software goes on "3rd Party" maintenance
Pete Mellor
o Re: Risks of spelling checkers
Joseph T Chew
Andrea Chen
Eric Sosman
o Re: Mud Slide Cuts East Coast Phones
David Lesher
o Aural Sex and Rudder Actuators
A. Padgett Peterson
o More jail-door openings
Tom Markson
o find/xargs strangeness
Peter J. Scott
Chris Dodd
o P. R. China Computer Security Rules
John Ho
o Info on RISKS (comp.risks)

A320 software goes on "3rd Party" maintenance

Pete Mellor <>
Fri, 1 Apr 94 23:52:42 BST
While I was in Copenhagen earlier today, a Danish friend, who knows of my
interest in the A320, drew to my attention an item in today's issue of the
news magazine "Goddaj" (if I recall the spelling correctly - it means "Good
Morning"). A translation of the article follows (courtesy of my Danish

   --------Translation of Article in "Goddaj", 1st April 1994 --------

                   Danish Firm Scores Notable "First"

Thor Avionics, one of Denmark's most advanced high-tech firms, has secured
a contract which makes it the first software house in the world to provide
"third party" maintenance on a major safety-critical software system.

In order to reduce the maintenance costs on its fleet of Airbus A320 aircraft
(the first type of civil airliner in the world to have a computer-controlled
"fly-by-wire" system), Air France has placed Thor under contract to provide
all future maintenance on the software of this highly-automated aircraft.

Wolf Larssen, director of Thor, said "This is the first contract of its type,
and it won't be the last. Users of commercial software long ago discovered
that there are great savings to be made by getting a "third party" firm to
maintain their software. I am only surprised that it has taken users of
safety-critical systems so long to discover the advantages. I expect other
A320 operators to be placing similar contracts before too long."

A "third-party" in this context means a firm which is independent of both the
user and the supplier. Such firms, being "lean and mean" are usually capable
of providing a much better and more cost-effective service than the original
supplier, since they have fewer overheads and are less stifled by bureaucracy.
In the commercial world, such contracts have usually gone to small, dynamic,
organisations, and it seems that the world of safety-critical software will
follow suite.

"We had to beat some stiff opposition from Sextant Avionique, Matra, Logica,
and similar large firms." said Mr. Larssen. "The fact that the software on the
A320 will need to be maintained indefinitely means guaranteed jobs for highly
qualified Danish workers for a long time to come."

M. Theophile Gautier, spokesman for Air France, said "We have the utmost
confidence in Thor to deliver the goods, both in terms of reduced cost,
improved system performance, and increased safety."

The automated systems on the A320, particularly the flight control and flight
management systems, have sometimes been called into question following the
various accidents involving this type of aircraft, although the accidents
have generally been ascribed to pilot error. Even so, there is an obvious
question mark over the ability of a third-party firm to maintain the level
of safety.

When asked about this, Mr. Larssen said "Our software maintenance and
validation process is second to none. Although Airbus Industrie have refused
to release the source code, so that we will have to strip out the binary and
work from that, we anticipate no problems. Most of the modifications we will
be making are fairly slight, so that regression testing can easily be done
on a software flight simulator running on an Apple MacKintosh."

A spokesman for the JAA (Joint Aviation Authority, which is responsible for
certifying that any new or modified design of aircraft is airworthy) said
"The basic design has already been certified. All that Thor will be doing
are minor post-certification modifications. Thor themselves have been
certified as conforming to the ISO-9000 quality standard and to SEI level 2,
so it should not be difficult for them to meet the requirements for our own
certification, which is based upon an industry standard referred to as

In response to questions about what the maintenance would actually involve,
Mr. Larssen said "Occasionally, Airworthiness Directives are issued by the
JAA which require changes to be made to the design of an aircraft in order
to correct a fault. Where this change involved modifying the software, Thor
will be responsible for doing this. The beauty of software is that the
modified version can be installed on all existing aircraft in seconds, simply
by inserting a new eprom. In addition to this corrective maintenance, we will
also be offering Air France enhancements to improve the performance of the
A320. The practice of "chipping", or modifying the firmware in the engine
management system of an automobile such as a BMW in order to make it go
faster, is well established. I don't expect that we could make your A320
perform like an F-111, but we could certainly extend the "safe flight
envelope" beyond the rather conservative limits originally set by the

         -------------------- Article Ends ------------------------

I leave it to readers to draw their own conclusions!

Peter Mellor, Centre for Software Reliability, City University, Northampton Sq
London EC1V 0HB   +44 (71) 477-8422,

   [This is quite a Thor-ny piece.  Incidentally, I note that "goddaj" is
   really "good day" (albeit used in the morning, as in the case of Guten
   Tag), and April 1 is certainly a "goddaj".  Unfortunately, occasional
   adjacent-key typing errors might easily replace the "j" with an "m", which
   might be an appropriate reaction.  PGN]

"I have a spelling checker, it came with my PC..."

Joseph T Chew <jtchew@Csa3.LBL.Gov>
Fri, 1 Apr 94 09:45:46 PST
> NAUSEA for NASA.  Singularly appropriate some days.

Microsoft Word's persistence in attempting to substitute Colada for Collider
certainly made me feel the need for a drink when writing about the SSC...


Re: Risks of spelling checkers

Fri, 1 Apr 94 11:17:19 -0500
The main risk is in relying too heavily on spell-checkers.  As people produce
more of their own documents, they no longer have someone who does most of the
proof-reading, and rely on a program instead.

Automation of other parts of document production has caused a change in the
type of errors that can get through.  Up until a few years ago, most errors in
trade books were switched letters ("b" for "d") probably caused by manual
typesetting.  Now one finds many more mistakes of a wrong word, no doubt from
a spell-checker substitution.  Perhaps we can ask, who checks the

-michael j zehr

Re: Risks of spelling checkers

Andrea Chen <>
1 Apr 1994 01:00:42 -0800
By definition, a spell checker is a product which eliminates a large set of
errors in a text. It does not eliminate them all.  I would suggest that you do
not go onto "auto pilot" when using the spell checker.  Instead use the same
level of awareness that you do when your write.  In fact it makes sense to
examine the text around every place the spell checker stops.  There are a lot
of errors which can only be eliminated by human attention.  As far as I can
see your general problem would not be eliminated by getting rid of profanity.
Suppose you had a "Ms. Gorse" in your document.  A spell checker might offer
"Goose".  Your client (or boss) might be equally offended.

Risk of Spelling Checkers

Eric Sosman x4425 <>
Fri, 1 Apr 94 13:23:55 EST
A company which sometimes competes with my employer sells a software
package which includes a spelling checker.  It flags 

Re: Mud Slide Cuts East Coast Phones (Re: RISKS-15.72)

David Lesher <>
Fri, 1 Apr 1994 10:28:32 -0500 (EST)
Note this took out a reported 200+ DS3 circuits. That's ~~100,000+
voice-grade circuits (if all were such).

Netcom's DC POP was one of the DS1's. They had leased the circuit from WilTel,
but WilTel in turn had subcontracted the facilities from MCI.  Further, while
MCI had the cable back up by 11pm, somehow WilTel did not communicate this to
Netcom. Thus the POP was not restored until the next morning. (Irony here -
WilTel got started pulling fiber through abandoned oil pipelines. Schedule 300
pipe provides much better than average protection against backhoe fade.)

Classic RISKs:
1) Too many eggs in one basket. While MCI surely has reserve capacity,
it does not seem to have 200 DS3's worth. No self-healing ring, it

2) Lost-in-translation syndrome - Once more than two organizations are
involved, the chances of getting any intact message from one end to the
other goes down as an exponential function of the number of hops.

ps: Ispell wants to turn "WilTel" into "Wilted"........

Aural Sex and Rudder Actuators (RISKS-15.72)

A. Padgett Peterson <>
Fri, 1 Apr 94 08:05:49 -0500
It is interesting that both of these incidents have a common thread -
no feedback loops.

Way back in the '70s when I was part of the team that designed the full
authority digital flight control system for the AFTI F-16, we had a similar
problem: the system was so complex and so many people were involved that it
was easy to miss the change that Jon made today would affect Harold's system -
and this was during the design stage. In production, component substitution
could have the same effect, some so subtle that it would not be noticed until
a pilot found himself in an interesting situation.

One of my tasks was to develop the simulation software used in a 40 foot
Evans & Sutherland dome & as such with each revision of the flight control
software, the appropriate changes had to be fed into the dome system.

In order to maintain continuity we developed a "configuration control model"
that simply scanned the source code for all uses of a variable or subroutine
and provided a map of the points of contact for each variable.  When a change
occurred, it was a simple matter to report the change to each affected
engineer/programmer. It was also an excellent tool for reporting when someone
had accidentally used the wrong variable in an equation since it would
suddenly show use in a routine it had not been used in before.

This tool also made it possible to notify those responsible for affected
modules when a component change was made since the tree for the variables
used with the component was readily available.

The process was really simple but deductive rather than inductive: changes
were detected not by people submitting a change notice but by a comparison
of "current" versus "last", active configuration management rather than
passive. Several times changes were found before the paperwork arrived.

The simple fact is that any large system, from a telephone number list to
aircraft fight controls is subject to Chaos math: small omissions over time
will increase in effect. Murphy says that unknown effects will be destructive.
Multiple omissions multiply effects.

The most effective answer I have found is active feedback loops, something
computers are very good at. Today one way I protect sites from intruder
attacks is by requiring modem registration and briefing of owners. I also
conduct random sweeps of the telephone lines looking for unregistered modems.
Without the second, the first would rapidly become obsolete. This has two
1) I find omissions quickly.
2) People are less likely to make omissions knowing that they will be noticed.

Over the last few years I have seem many instances in RISKS of problems with
aircraft flight controls making the wrong decision or telling the pilot
the wrong thing and each time have wondered if active design or configuration
management feedback loops could have prevented them.


More jail-door openings

Tom Markson <>
Fri, 1 Apr 1994 12:54:43 -0800 (PST)
I saw on San Francisco's channel 4 last night that a jail in Marin which
houses such people as Polly Klaus' killer has been having problems with
their cell doors.  Apparently, without reason, they would just open.
The prison said their was no danger in escape.  They blamed the problem
on "software errors".

How about that?


RISKS Forum <>
Fri, 1 Apr 94 14:27:06 PST
The RISKS archives include the following items from the ACM SIGSOFT Software
Engineering Notes (S vol i no j).  Recent items also appear in the on-line

..... Prison problems
 Seven Santa Fe inmates escaped; prison control computer blamed (S 12 4)
 Oregon prisoner escaped; frequent-false-alarm alarm ignored (S 12 4)
 New Dutch computer system frees criminals, arrests innocent; old system
   eliminated, and no backup possible! (S 12 4)
 New El Dorado jail cell doors won't lock -- computer controlled (S 13 4)
 San Joaquin CA jail doors unlocked by spurious signal; earlier, inmates
   cracked Pelican Bay State Prison pneumatic door system (S 18 2:4)

find/xargs strangeness

Peter J. Scott <>
1 Apr 1994 21:10:38 GMT
Man, just when I thought I understood this stuff.  I have condensed
this down to the following:

euclid% euclid% mkdir something_scwewy
euclid% cd !$
euclid% foreach i (a b c d)
? echo $i > $i
? end
euclid% find . -type f -print | xargs -n1 more
--More--(Next file: ./a)          # Hit <SPACE>

Now, to my way of thinking, it should be executing the commands "more ./a;
more ./b; more ./c; more ./d".  Certainly I have had and come to expect this
sort of behavior from xargs in the past.  It seems to be a problem with
"more", because I get decent behavior with, say, "echo" and "cat":

euclid% find . -type f -print | xargs -n1 cat

euclid% find . -type f -print | xargs -t -n1 more
more ./a

BTW, if there are more than a screenful of files, I get prompted by
more to scroll through the list of them before it actually runs
more on the first file.  I don't get this at all.  This is on SunOS 4.1.3.

Peter Scott, NASA/JPL/Caltech    (

Re: Peter J. Scott: find/xargs strangeness]

Chris Dodd <>
Fri, 1 Apr 94 15:05:31 -0800
This is an example of a strange interaction of two bugs, one in `more' and one
in `xargs'.  All bugs are RISKS to some extent, its not clear how severe or
unusual they need to be to make it into RISKS...

There are two strange things occurring here.
1. When `more' is invoked with its standard input connected to something
   OTHER than a terminal, it treats `stdin' as the first file to display.
2. `xargs' doesn't close the input to the child it invokes.

So what happens is, `xargs' invokes `more ./a', and `more' reads everything
it can from its standard input, which connects to the `find'.  When
`more' finishes, `xargs' finds that its `stdin' is empty and exits.

To exercise these bugs separately, try:
echo a b c | more ./a
echo a b c d | xargs -n1 cat -

Chris Dodd

P. R. China Computer Security Rules (long)

<[a known contributor who wishes to remain anonymous]>
Fri, 1 Apr 1994 12:22:17 (xxT)
connection to the Internet (CHINANET; sub CHINANET to

The Chinese have named their new project to connect China to the Internet the
"Golden Bridge" project.  The following document purports to be the newly
developed "PRC Regulations on Safeguarding Computer Information Systems."  It
seems quite appropriate for RISKS.

As you read this, keep in mind that 1) in China accused persons are guilty
until proven innocent; 2) laws referred to in the document as ones applying in
certain circumstances are often harsh, subject to change without notice, and
so vaguely worded as to make easy the prosecutor's job, not of proving guilt
(not necessary), but of arguing why the penalty should be maximized; 3) the
"Public Security" laws referred to are the same laws that stipulate that the
families of serious offenders will be billed for the single bullet used in
judgement; 4) certain concepts (virus, special security products) are either
poorly defined or all inclusive; 5) in China when there is doubt as to the
legality of any particular act, illegality is assumed (this is important not
only in court, but also in normal life, where people tend to be more
conservative in part because of it.)

As we welcome this brave new domain into our net.universe, it will be
interesting, and perhaps surprising at times, to see how another set of
explorers on the electronic frontier are approaching the flow of information.
Golden Bridge, indeed.  As read, sending email without filing a customs
declaration, or accepting a shareware registration for an anti- virus product
could both be construed as being illegal.  There's a lot of room for
improvement here, imho.

P.R.C. Regulations on Safeguarding Computer Information Systems

Source: Beijing XINHUA Domestic Service in Chinese, February 23, 1994
From: (John Ho), Asia Online

Chapter I. General Provisions

Article 1. These regulations have been formulated to safeguard computer
information systems, to promote the application and development of computers,
and to ensure smooth progress in socialist modernization.

Article 2. The computer information systems referred to in these regulations
are man-machine systems, composed of computers and their allied and peripheral
equipment and facilities (including networks), that collect, process, store,
transmit, and retrieve information according to prescribed goals and rules of

Article 3. In safeguarding computer information systems, measures shall be
taken to secure computers, allied and peripheral equipment and facilities
(including networks), the operating environment, and data, as well as to
ensure the normal functioning of computers, so as to safeguard the safe
operation of computer information systems .

Article 4. In safeguarding computer information systems, priority shall be
given to the security of computer systems containing data on such important
areas as state affairs, economic construction, national defense, and
state-of-the-art science and technology.

Article 5. These regulations shall apply to safeguarding computer information
systems within the PRC's borders.

Measures for safeguarding microcomputers that have not been hooked up shall be
enacted separately.

Article 6. The Ministry of Public Security shall be in charge of safeguarding
computer information systems.

The Ministry of State Security, the State Secrecy Bureau, and relevant State
Council departments shall carry out work pertaining to safeguarding computer
information systems within the lines of authority prescribed by the State

Article 7. No organization or individual may use computer information
systems to engage in activities that endanger national or collective
interests, as well as the legitimate interests of citizens; they
may not jeopardize computer information systems.

Chapter II. The Safeguards System

Article 8. Computer information systems shall be established and applied in
accordance with laws, administrative rules, and relevant state provisions.

Article 9. Computer information systems shall be protected on the basis of
security grades. The Ministry of Public Security, in conjunction with relevant
departments, shall establish security grades and formulate specific measures
for protection based on such grades.

Article 10. Computer rooms shall conform to state norms and relevant state

No work may be carried out in the vicinity of computer rooms that jeopardizes
computer information systems.

Article 11. Units using internationally networked computer information systems
shall register their systems with the public security departments of people's
governments at or above the provincial level.

Article 12. Individuals who ship, bring, or mail computer information media
into or out of the country shall file truthful declarations with the customs

Article 13. Units that use computer information systems shall establish
security management systems and assume responsibility for safeguarding their
computer information systems.

Article 14. Units that use computer information systems shall report any
incidents relating to their systems to the public security departments of
local people's governments at or above the county level within 24 hours of the

Article 15. The Ministry of Public Security shall exercise centralized
management over research into the control and prevention of computer viruses
and other harmful data that jeopardizes public security.

Article 16, The state shall implement a licensing system for the sale of
special safety products for computer information systems.  The Ministry of
Public Security shall enact specific measures in conjunction with relevant

Chapter III. Supervision Over Security

Article 17. Public security organs shall perform the following functions to
supervise efforts to safeguard computer information systems:

(1) Supervising, inspecting, and guiding the work of safeguarding computer
information systems;

(2) Investigating and dealing with illegal and criminal cases involving the
endangerment of computer information systems; and

(3) Other supervisory functions with regard to safeguarding computer
information systems.

Article 18. Upon detecting latent hazards in computer information systems,
public security organs shall promptly advise the units that use such systems
to institute safety measures.

Article 19. Under urgent circumstances, the Ministry of Public Security may
issue special circulars on specific security aspects of computer information

Chapter IV. Legal Responsibilities

Article 20. In the event of any of the following violations of the provisions
in these regulations, public security organs shall issue warnings or shut down
the computers for screening purposes:

(1) Contravening the system for protecting computer information systems based
on security grades and jeopardizing computer information systems;

(2) Violating the registration system for internationally networked computer
information systems;

(3) Failing to report incidents related to computer information systems within
the prescribed time frames;

(4) Failing to take remedial action within the prescribed time after receiving
notification from public security organs mandating security improvement

(5) Other actions endangering computer information systems.

Article 21. Public security organs, in conjunction with relevant units, shall
deal with cases in which computer rooms do not conform to state norms or
relevant state provisions, or in which work carried out in the vicinity of
computer rooms endangers computer information systems.

Article 22. The customs authorities shall deal with failure to file truthful
declarations on computer information media shipped, brought, or mailed into or
out of the country, pursuant to the "PRC Customs Law" and the provisions
outlined in these regulations and other laws and regulations.

Article 23. Public security organs shall issue warnings or impose fines of not
more than 5,000 yuan and 15,000 yuan, respectively, on individuals or units if
computer viruses or other data harmful to computer information systems are
deliberately input into such systems, or if special safety products for
computer information systems are sold without permission. They shall
confiscate illegal proceeds and impose a fine that is 100 or 300 percent more
than the sum of such proceeds.

Article 24. Actions that violate the provisions in these regulations and
constitute infractions of public security shall be punished pursuant to
relevant provisions in the "PRC Regulations on Security Administration and
Punishment"; if the actions constitute a crime, criminal responsibilities
shall be investigated.

Article 25. Any organization or individual who inflicts property losses on the
state, collectives, or other individuals in violation of the provisions in
these regulations shall assume civil responsibility in accordance with the

Article 26. Interested parties who are dissatisfied with specific
administrative actions carried out by public security organs pursuant to these
regulations may apply for administrative reconsideration in accordance with
the law or file administrative lawsuits.

Article 27. Government functionaries who abuse their power to demand and take
bribes or commit other illegal or delinquent acts while enforcing these
regulations shall be punishable on criminal grounds if their actions
constitute crimes or given disciplinary actions if their actions do not
constitute crimes.

Chapter V. Supplementary Provisions

Article 28. The meanings of terms used in these regulations are defined as

Computer viruses mean a set of self-replicating computer commands or
programming codes inserted during the course of programming or into computer
programs that can impair computer functions, destroy data, or affect computer

Special safety products for computer information systems mean special hardware
and software products for use in safeguarding computer information systems.

Article 29. Military-related computer information systems shall be safeguarded
in accordance with relevant military laws and regulations.

Article 30. The Ministry of Public Security may formulate implementation
measures in accordance with these regulations.

Article 31. These regulations shall take effect upon promulgation.

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