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 12 Issue 01

Monday 1 July 1991


o The Risks of Undelete and the Law
Ron Dippold
o Patriot missile specifications
Robert I. Eachus
o Lawsuit Pending over Patriot's Failure to Stop Dharan Scud
Sean Smith
o Word Perfect file locking poor protection
John Gilmore and Helen Bergen via Peter Jones
o Statement in Support of Communications Privacy
John Gilmore
o NIST announces public-key digital signature standard
John Gilmore
o Re: Videotape of the pilot discussing the crash of UAL 232
Robert Dorsett
o Info on RISKS (comp.risks)

The Risks of Undelete and the Law

Ron Dippold <>
Thu, 20 Jun 91 06:24:27 GMT
Here's one about a class A dummy...  You'd think he'd be a bit more careful
on something like this.

Probably the most dramatic instance of recovery of "deleted" file information
appears in a recent ruling of the Pennsylvania Supreme Court, Com. v.
Copenhefer, 587 A.2d 1353.  The defendant's death sentence was affirmed on
"overwhelming" circumstantial evidence, including "incredibly comprehensive"
evidence seized from the defendant's home pursuant to search warrants.

The computer evidence consisted of drafts of texts of phone calls, ransom and
hidden notes, and a 22 point plan for the kidnapping scheme, which eventuated
in murder of a bank manager's wife.  (The defendant was a bookstore owner who
had "unproductive transactions" with the bank).

The defendant argued that the computer evidence should have been suppressed
because he had deleted the files, thereby creating an "expectation of privacy"
under _Katz_ and its progeny.  The court's opinion contains a readable
explanation of how the deletion only affected the directory, and "subsequent
usage never displaced the files in question and they remained in the memory of
his computer."

The court soundly, and IMO correctly, rejected this claim, analogizing the
retrieval of the deleted file data (by an FBI agent who was a computer expert)
to deciphering a coded message in a diary, after the diary was obtained under a
valid subpoena.

Somehow, I don't think Mr. Copenhefer will be doing any endorsements for
PCTools or another defragmenter; "if only I had used Compress with the Clear
option, I wouldn't be on death row now." Among other things, the old-fashioned
physical evidence was quite overwhelming.  But the case is a striking example
of the law adjusting to computer technology.

Sort of unbelievable, especially the part about an FBI computer expert (maybe
they borrowed someone from the NSA?), but true!  So remember, Norton WIPEDISK
is your friend.
                                       Ron Dippold

Patriot missile specifications

Robert I. Eachus <>
Wed, 19 Jun 91 12:29:39 EDT
     There has been some tendancy here to treat the Patriot system "failure" to
intercept the El Hussein missile in Dharan as a poor system specification or as
badly designed software.  This is totally wrong.  If someone had gone to the
Army before the Gulf War and asked, "In this hypothetical
should the system respond?"  The answer would have been to do as it did.

     The "problems" in the software were bugs only AFTER it was known IN
PRACTICE that 1) there were missiles in that speed range that could and should
be attacked, 2) the Patriot systems' primary mission would NOT be defending
against hostile aircraft, and 3) that "highly motivated" and experienced crews
could successfully engage such missiles in "manual" mode using information from
other sites.  Given those circumstances updating the software and getting it to
the field in a matter of days was a heroic effort, even if it arrived one day
too late.

     The real risk here is in assuming that the "fog of war" is a myth.  You
don't know how systems will be used in practice until you have actual combat
experience.  I have seen many "field mods" to hardware incorporated into later
production models because the feature was needed to use the system to best
effect in combat.  This is NOT a failure of design or specification or
production, it is often the result of someone trying something because he is
dead anyway if it doesn't work.  Such successful tactics quickly become the
normal way the weapon is used.

     A simple example is dive brakes, which were initially installed on P-38s
after many crashed from incompressability problems.  In combat, the only
advantage that the P-38 had in some situations over its opponent was the
ability to dive faster, so pilots took it to the limit and beyond.  The dive
brake was invented to "fix" a problem which only occurred when a pilot stayed
in a steep dive at full power too long.  (Actually, there was a "known fix" by
the time the brakes were available--fly an outside loop!) If dive brakes had
existed when the plane was designed the designers would have been told to leave
them off.  No reason to add weigth to the plane, and no sane pilot would do
something like that anyway...  Of course, after experence in combat, pilots
would carry as much weight as possible, and try to use it to save their lives.

Lawsuit Pending over Patriot's Failure to Stop Dharan Scud

Wed, 19 Jun 91 12:26:33 EDT
About half the US soldiers killed in the Dharan Scud attack belonged to a unit
stationed outside of Pittsburgh.  Recently, the local news has been reporting
that a Pittsburgh area law firm is recruiting the families of the deceased to
participate in a class action lawsuit against Raytheon, manufacturers of the
Patriot missile defense system.

Considering that the system was being operated out of spec, to solve a
different difficult problem (defense of a city) than the one it was designed
for (point defense), this incident suggests that writing software may be
RISKier than we thought...

Word Perfect file locking poor protection

Tue, 25 Jun 91 19:52:19 EDT
A file on the SIMTEL20 archives, PD:<MSDOS.INFO>UNCRYPT.ZIP, gives information
on how to break files that a WP user has "locked" with a password, in WP lingo.
Here are some excerpts pertinent to RISKS.

From: gnu@hoptoad.uucp (John Gilmore)
Newsgroups: comp.os.msdos.apps,sci.crypt
Subject: Word Perfect "locked document encryption" is trivial to break
Date: 27 Aug 90 22:58:27 GMT
Organization: Cygnus Support, Palo Alto

One thing that came up at Crypto '90 was a short paper from Ms. Helen Bergen at
Queensland U. in Australia.  She noticed the 'locked document' commands in Word
Perfect, used by all the secretaries in her dept., and looked to see how strong
it was.  It turned out that the MSDOS DEBUG command and an envelope for scratch
paper are enough for anyone to decode both a document AND the key used for it!
Word Perfect Corp. didn't care about her results (letter reproduced below), but
I thought that some Word Perfect losers, I mean users, here on the net might
want to know.

You should consider WP locked documents like ROT13: fine to keep the text
garbled until you type a command, useless for keeping things private.

        John Gilmore

From: <>
Date: Mon, 27 Aug 90 10:28 +1000
To: cygint!gnu

Dear John,

   Here is the letter and a copy of the Latex source of my paper. It
will be published in CRYPTOLOGIA in the near future. Thanks for your

      Helen Bergen

Quote from letter received from WordPerfect Pacific:

Thankyou for the copy of your paper entitled "File Security in WordPerfect
5.0". I sent a copy of the paper to WordPerfect Corporation in the USA and
recently received a reply from them.

They confirmed that people have written programs to break the password.
However, WordPerfect Corporation does not have such a program and therefore has
no way of breaking it. They also pointed out that very few users would know how
to write such a program.

It is possible that the manual may be amended in a future edition to clarify
the protection that a password gives. They recommend that anyone concerned
about security may want to take higher precautions than the password

Thank you for your interest in WordPerfect.


        H.A. Bergen     School of Computing Science
        W.J. Caelli     Information Security Research Centre

           Faculty of Information Technology
           Queensland University of Technology
           G.P.O. Box 2434, Brisbane, Q 4001, AUSTRALIA

ABSTRACT: Cryptanalysis of files encrypted with the 'locked document'
option of the word processing package WordPerfect V5.0, is shown to be
remarkably simple.  The encryption key and the plaintext are easily
recovered in a ciphertext only attack. File security is thus
compromised and is not in accord with the claim by the manufacturer
that: "If you forget the password, there is absolutely no way to
retrieve the document".

KEYWORDS: Cryptanalysis, WordPerfect.


WordPerfect is one of the most popular word processing packages in use today.
It has a 'locked document' option which aims at protection of a WordPerfect
file from unauthorised access. The manual states "You can protect or lock your
documents with a password so that no one will be able to retrieve or print the
file without knowing the password - not even you".  The manual also claims that
"If you forget the password, there is absolutely no way to retrieve the
document" [1].

[detailed explanation omitted]

In the 4.2 version, the only text encrypted was that contained in the actual
document. This is unknown plaintext. In version 5.0, however, the printer
information as well as the document text is encrypted.  We have identified
bytes 16 - 21, 24 - 27, 29 - 41, 43 - 45 as being constant for a particular
system (as defined earlier, a particular licenced copy of WordPerfect on a
particular PC and printer), and they do not change markedly from one system to

So we have the ideal situation of known plaintext for a reasonable number of
bytes.  This can greatly simplify our attack as it makes it possible to recover
the actual key. Then it is trivial to recover the plaintext by using
WordPerfect to retrieve the file using the recovered key as the ''password''.
Alternatively, a program could be written to do this as the
encryption/decryption algorithm is known.  We outline a strategy with the
following example from one particular system:

[detailed explanation of finding the key omitted]

  *  Retrieve the plaintext using WordPerfect with the
key as the password. This is the easiest way to decrypt
the document text.

  *  If no access to WordPerfect is available, then it is
straightforward to recover the plaintext with a short C
program which implements the decryption algorithm as described
previously. This has been done successfully.


The encryption key is easily recovered in an apparent KNOWN CIPHERTEXT ONLY
attack, as the system provides enough known plaintext in the printer
information regardless of the document plaintext.  The analysis, as shown, can
literally be done on the back of a (large) envelope.

The analysis may be slightly more difficult where the physical system on which
the files were prepared is completely unknown and vastly different to any
system we have encountered, as this may reduce the amount of known plaintext.
In these situations, statistical analysis based on the characteristic
frequencies of characters in a language is used to decipher text files.  This
is a standard method which is straightforward although a program may have to be

In summary, the cryptanalysis of files encrypted with the 'locked document'
option in WordPerfect version 5.0 is remarkably simple.  The inclusion of
portions of known plaintext in the encrypted file is a fatal flaw in the
system, since it provides a mechanism of attack in which the key can be
recovered by hand, and document plaintext easily retrieved.  All of the key can
easily be recovered for keylengths of 1-13 and 15-17, far in excess of commonly
used passwords of 8 characters.  A high proportion of the key can be deduced
for keylengths of 14 and 18-24.  The cipher used is too weak, providing little
or no protection.

If the attacker has knowledge of any other unencrypted file from the same
system, the analysis is made even more simple.  We stress that **both the key
and the plaintext can be recovered**, independent of the content of the

The worst problem is that it may give a false sense of security. For example,
an attacker may decrypt a document, modify it and re-encrypt so that the
originator is unaware of the alterations.  We conclude that the file security
is not consistent with claims made by the manufacturer and is not sufficent to
protect sensitive documents from anything but the most naive attack.


1. WORDPERFECT CORPORATION (1989): WordPerfect for IBM Personal
2. BENNETT, J (1987): Analysis of the encryption algorithm
used in the WordPerfect Word Processing Program,
Cryptologia, Vol XI. No 4. pp 206-210.\\
3. KONHEIM, A G (1981): {\em Cryptography, A Primer}, Wiley.\\
4. DENNING, D E (1981): {\em Cryptography and Data Security},
Addison Wesley.\\
5. CARROLL, J and Robbins, L E (1989): Computer Cryptanalysis
of Product Ciphers, Cryptologia, Vol XIII. No 4. pp 303-326.\\


Helen Bergen is a Lecturer in the School of Computing Science, Faculty of
Information Technology, at the Queensland University of Technology.  Her
research interests within the Information Security Research Centre, Faculty of
Information Technology, include cryptology and the application of

Bill Caelli is Director of the Information Security Research Centre within the
Faculty of Information Technology at the Queensland University of Technology.
He is also Technical Director and Founder of ERACOM Pty. Ltd., a manufacturer
of cryptographic equipment. His research interests lie in the development and
application of cryptographic systems to enhance security, control and
management of computer and data network systems.  -- John Gilmore
 The Gutenberg Bible is printed on hemp (marijuana) paper.  So was the July 2,
  1776 draft of the Declaration of Independence.  Why can't we grow it now?

Peter Jones                    (514)-987-3542
Internet:Peter Jones <>
UUCP: ...psuvax1!uqam.bitnet!maint

Statement in Support of Communications Privacy

Tue, 18 Jun 91 22:27:11 -0700
The Electronic Frontier Foundation, Computer Professionals for Social
Responsibility, and RSA Data Security Inc. cosponsored a meeting of
cryptographers, civil libertarians, business leaders, and people from
all over the government who handle cryptography and privacy issues.
The following statement was released at the meeting.

            Washington, DC
             June 10, 1991

    As representatives of leading computer and telecommunications
companies, as members of national privacy and civil liberties organizations, as
academics and researchers across the country, as computer users, as corporate
users of computer networks, and as individuals interested in the protection of
privacy and the promotion of liberty, we have joined together for the purpose
of recommending that the United States government undertake a new approach to
support communications privacy and to promote the availability of
privacy-enhancing technologies.  We believe that our effort will strengthen
economic competitiveness, encourage technological innovation, and ensure that
communications privacy will be carried forward into the next decade.

    In the past several months we have become aware that the federal
government has failed to take advantage of opportunities to promote
communications privacy.  In some areas, it has considered proposals that would
actually be a step backward.  The area of cryptography is a prime example.

    Cryptography is the process of translating a communication into a code
so that it can be understood only by the person who prepares the message and
the person who is intended to receive the message.  In the communications
world, it is the technological equivalent of the seal on an envelope.  In the
security world, it is like a lock on a door.  Cryptography also helps to ensure
the authenticity of messages and promotes new forms of business in electronic
environments.  Cryptography makes possible the secure exchange of information
through complex computer networks, and helps to prevent fraud and industrial

    For many years, the United States has sought to restrict the use of
encryption technology, expressing concern that such restrictions were necessary
for national security purposes.  For the most part, computer systems were used
by large organizations and military contractors.  Computer policy was largely
determined by the Department of Defense.  Companies that tried to develop new
encryption products confronted export control licensing, funding restrictions,
and classification review.  Little attention was paid to the importance of
communications privacy for the general public.

    It is clear that our national needs are changing.  Computers are
ubiquitous.  We also rely on communication networks to exchange messages daily.
The national telephone system is in fact a large computer network.

    We have opportunities to reconsider and redirect our current policy on
cryptography.  Regrettably, our government has failed to move thus far in a
direction that would make the benefits of cryptography available to a wider

    In late May, representatives of the State Department met in Europe with
the leaders of the Committee for Multilateral Export Controls ("COCOM").  At
the urging of the National Security Agency, our delegates blocked efforts to
relax restrictions on cryptography and telecommunications technology, despite
dramatic changes in Eastern Europe.  Instead of focusing on specific national
security needs, our delegates continued a blanket opposition to secure network
communication technologies.

    While the State Department opposed efforts to promote technology
overseas, the Department of Justice sought to restrict its use in the United
States. A proposal was put forward by the Justice Department that would require
telecommunications providers and manufacturers to redesign their services and
products with weakened security.  In effect, the proposal would have made
communications networks less well protected so that the government could obtain
access to all telephone communications.  A Senate Committee Task Force Report
on Privacy and Technology established by Senator Patrick Leahy noted that this
proposal could undermine communications privacy.

    The public opposition to S. 266 was far-reaching.  Many individuals
wrote to Senator Biden and expressed their concern that cryptographic equipment
and standards should not be designed to include a "trapdoor" to facilitate
government eavesdropping.  Designing in such trapdoors, they noted, is no more
appropriate than giving the government the combination to every safe and a
master key to every lock.

    We are pleased that the provision in S. 266 regarding government
surveillance was withdrawn.  We look forward to Senator Leahy's hearing on
cryptography and communications privacy later this year.  At the same time, we
are aware that proposals like S. 266 may reemerge and that we will need to
continue to oppose such efforts.  We also hope that the export control issue
will be revisited and the State Department will take advantage of the recent
changes in East-West relations and relax the restrictions on cryptography and
network communications technology.

    We believe that the government should promote communications privacy.
We therefore recommend that the following steps be taken.

    First, proposals regarding cryptography should be moved beyond the
domain of the intelligence and national security community.  Today, we are
growing increasingly dependent on computer communications.  Policies regarding
the appropriate use of cryptography should be subject to public review and
public debate.

    Second, any proposal to facilitate government eavesdropping should be
critically reviewed.  Asking manufacturers and service providers to make their
services less secure will ultimately undermine efforts to strengthen
communications privacy across the country.  While these proposals may be based
on sound concerns, there are less invasive ways to pursue legitimate government

    Third, government agencies with appropriate expertise should work free
of NSA influence to promote the availability of cryptography so as to ensure
communications privacy for the general public.  The National Academy of Science
has recently completed two important studies on export controls and computer
security.  The Academy should now undertake a study specifically on the use of
cryptography and communications privacy, and should also evaluate current
obstacles to the widespread adoption of cryptographic protection.

    Fourth, the export control restrictions for computer network technology
and cryptography should be substantially relaxed.  The cost of export control
restrictions are enormous.  Moreover, foreign companies are often able to
obtain these products from other sources. And one result of export restrictions
is that US manufacturers are less likely to develop privacy-protecting products
for the domestic market.

    As our country becomes increasingly dependent on computer
communications for all forms of business and personal communication, the need
to ensure the privacy and security of these messages that travel along the
networks grows.  Cryptography is the most important technological safeguard for
ensuring privacy and security.  We believe that the general public should be
able to make use of this technology free of government restrictions.

    There is a great opportunity today for the United States to play a
leadership role in promoting communications privacy.  We hope to begin this
process by this call for a reevaluation of our national interest in
cryptography and privacy.

Mitchell Kapor, Electronic Frontier Foundation
Marc Rotenberg, CPSR
John Gilmore, EFF
D. James Bidzos, RSA
Phil Karn, BellCore
Ron Rivest, MIT
Jerry Berman, ACLU
Whitfield Diffie, Northern Telecom
David Peyton, ADAPSO
Ronald Plesser, Information Industry Association
Dorothy Denning, Georgetown University
David Kahn, author *The Codebreakers*
Ray Ozzie, IRIS Associates
Evan D. Hendricks, US Privacy Council
Priscella M. Regan, George Mason University
Lance J. Hoffman, George Washington University
David Bellin, Pratt University
     (affiliations are for identification purposes only)

NIST announces public-key digital signature standard

Thu, 27 Jun 91 11:39:59 -0700
    Statement of Raymond G. Kammer, Deputy Director
    National Institute of Standards and Technology
    Before the Subcommittee on Technology and Competitiveness
    of the Committee on Science, Space, and Technology
    On Computer Security Implementation
    House of Representatives,   June 27, 1991

Digital Signature Standard

I know that you are interested in our progress in developing a federal digital
signature standard based upon the principles of public-key cryptography.  I am
pleased to tell you that we are working out the final arrangements on the
planned standard, and hope to announce later this summer our selection of a
digital signature standard based on a variant of the ElGamal signature

Our efforts in this area have been slow, difficult, and complex.  We evaluated
a number of alternative digital signature techniques, and considered a variety
of factors in this review: the level of security provided, the ease of
implementation in both hardware and software, the ease of export from the U.S.,
the applicatility of patents and the level of efficiency in both the signature
and verification functions that the technique performs.

In selecting digital signature technique method [sic], we followed the mandate
contained in section 2 of the Computer Security Act of 1987 to develop
standards and guidelines that ". . . assure the cost-effective security and
privacy of sensisive information in Federal systems."  We placed primary
emphasis on selecting the technology that best assures the appropriate security
of Federal information.  We were also concerned with selecting the technique
with the most desirable operating and use characteristics.

In terms of operating characteristics, the digital signature technique provides
for a less computational-intensive signing function than verification function.
This matches up well with anticipated Federal uses of the standard.  The
signing function is expected to be performed in a relatively computationally
modest environment such as with smart cards.  The verification process,
however, is expected to be implemented in a computationally rich environmnet
such as on mainframe systems or super-minicomputers.

With respect to use characteristics, the digital signature technique is
expected to be available on a royalty-free basis in the public interest
world-wide.  This should result in broader use by both government and the
private sector, and bring economic benefits to both sectors.

A few details related to the selection of this technique remain to be worked
out.  The government is applying to the U.S. Patent Office for a patent, and
will also seek foreign protection as appropriate.  As I stated, we intend to
make the technique available world-wide on a royalty-free basis in the public

A hashing function has not been specified by NIST for use with the digital
signature standard.  NIST has been reviewing various candidate hashing
functions; however, we are not satisfied with any of the functions we have
studied thus far.  We will provide a hashing function that is complementary to
the standard.

I want to speak to two issues that have been raised in the public debate over
digital signature techniques.  One is the allegation that a "trap door", a
method for the surreptitious defeat of the security of this system, has been
built into the technique that we are selecting.  I state categorically that no
trap door has been designed into this standard nor does the U.S. Government
know of any which is inherent in the ElGamal signature method that is the
foundation of our technique.

Another issue raised is the lack of public key exchange capabilities.  I
believe that, to avoid capricious activity, Public Key Exchange under control
of a certifying authority is required for government applications.  The details
of such a process will be developed for government/industry use.

NIST/NSA Technical Working Group

Aspects of digital signature standard were discussed by the NIST/NSA Technical
Working Group, established under the NIST/NSA Memorandum of Understanding. The
Working Group also discussed issues involving the applicability of the digital
signature algorithm to the classified community, cryptographic key management
techniques, and the hashing function to be used in conjunction with the digital
signature standard.  Progress on these items has taken place; however, as with
the digital signature standard, non-technical issues such as patents and
exportability require examination, and this can be a lengthy process.  We have
found that working with NSA is productive.  The Technical Working Group
provides an essential mechanism by which NIST and NSA can conduct the technical
discussions and exchange contemplated by the Computer Security Act and also
allows us to address important issues drawing upon NSA's expertise.

Re: Videotape of the pilot discussing the crash of UAL 232

Robert Dorsett <>
Sat, 29 Jun 91 00:28:11 CDT
>There's been a lot of discussion of the safety of fly-by-wire aircraft, so
>here's the discussion of an accident that very possibly would have been
>prevented were the DC-10 fly-by-wire rather than hydraulic.

As I'm sure Mary realizes, FBW does not alleviate the necessity for multiple-
redundant hydraulics, and all the plumbing that comes with them.  As currently
implemented on most aircraft, it simply replaces the means by which the
*hydraulic* actuators are operated.  Instead of cables, there are electrical
wires.  These leads to one or more computers, which in turn process command
inputs from the pilot, leading to the possibility of unconventional control
laws.  Most of the controversy of FBW occurs at this stage.  The severity of
the failure involved would have happened whether the DC-10 were FBW or not.

Now, in rebuttal, I'm sure Mary'd point out that the FBW issue would only
enter in the form of *control* issues subsequent to the accident, introducing
unconventional control laws to effectively duplicate (or improve upon) the
differential thrust technique Haynes used.  And she has a point.  But there's
always the question of whether the complexity and cost of such software will
ever justify its usefulness in the "1:1e-9" catastrophic control failure
case.  In safety management, there is a point of negative return.

Perhaps a more salient observation would have been: this accident would not
have happened if there was full manual reversion on the DC-10, ala the Boeing
707? :-)

Robert Dorsett Internet: UUCP:!!rdd

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