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>Chapter 5. Topics</H1
><P
>This chapter covers miscellaneous topics that do not fit
elsewhere in the user manual.
As topics are added, they may be collected and factored into chapters
that stand on their own.
If you would like to see a particular topic covered, please suggest it.
Even better, volunteer to write a first draft covering your suggested topic!</P
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><A
NAME="AEN574"
>Writing user interfaces</A
></H1
><P
><A
HREF="http://www.cs.cmu.edu/~alma"
TARGET="_top"
>Alma Whitten</A
> and 
<A
HREF="http://www.cs.berkeley.edu/~tygar"
TARGET="_top"
>Doug Tygar</A
> have done a 
<A
HREF="http://reports-archive.adm.cs.cmu.edu/anon/1998/abstracts/98-155.html"
TARGET="_top"
>study</A
>
on NAI's PGP 5.0 user interface and came to the conclusion 
that novice users find PGP confusing and frustrating.
In their human factors study, only four out of twelve test subjects
managed to correctly send encrypted email to their team members, 
and three out of twelve emailed the secret without encryption. 
Furthermore, half of the test subjects had a technical background.</P
><P
>These results are not surprising.
PGP 5.0 has a nice user interface that is excellent if you already
understand how public-key encryption works and are familiar with
the web-of-trust key management model specified by OpenPGP.
Unfortunately, novice users understand neither public-key encryption
nor key management, and the user interface does little to help.</P
><P
>You should certainly read Whitten and Tygar's report if you are writing
a user interface.
It gives specific comments from each of the test subjects, and those
details are enlightening. 
For example, it would appear that many of subjects believed that a
message being sent to other people should be encrypted to the test
subject's own public key.
Consider it for a minute, and you will see that it is an easy mistake
to make.
In general, novice users have difficulty understanding the different
roles of the public key and private key when using GnuPG.
As a user interface designer, you should try to make it clear at 
all times when one of the two keys is being used.
You could also use wizards or other common GUI techniques for
guiding the user through common tasks, such as key generation, where
extra steps, such as generating a key revocation certification and 
making a backup, are all but essential for using GnuPG correctly.
Other comments from the paper include the following.
<P
></P
><UL
><LI
><P
>Security is usually a secondary goal; people want to send
email, browse, and so on.  
Do not assume users will be motivated to read manuals or go 
looking for security controls.</P
></LI
><LI
><P
>The security of a networked computer is only as strong as its 
weakest component. 
Users need to be guided to attend to all aspects of their security, 
not left to proceed through random exploration as they might with a 
word processor or a spreadsheet.</P
></LI
><LI
><P
>Consistently use the same terms for the same actions.
Do not alternate between synonyms like ``encrypt'' and 
``encipher''.</P
></LI
><LI
><P
>For inexperienced users, simplify the display. 
Too much information hides the important information.
An initial display configuration could concentrate on giving
the user the correct model of the relationship between public 
and private keys and a clear understanding of the functions 
for acquiring and distributing keys.</P
></LI
></UL
></P
><P
>Designing an effective user interface for key management is even more
difficult.
The OpenPGP web-of-trust model is unfortunately quite obtuse.
For example, the specification imposes three arbitrary trust levels
onto the user: none, marginal, and complete.
All degrees of trust felt by the user must be fit into one of those
three cubbyholes.
The key validation algorithm is also difficult for non-computer scientists
to understand, particularly the notions of ``marginals needed'' and
``completes needed''.
Since the web-of-trust model is well-specified and cannot be changed,
you will have to do your best and design a user interface that helps
to clarify it for the user.
A definite improvement, for example, would be to generate a diagram of how
a key was validated when requested by the user.
Relevant comments from the paper include the following.
<P
></P
><UL
><LI
><P
>Users are likely to be uncertain on how and when to grant accesses.</P
></LI
><LI
><P
>Place a high priority on making sure users understand their
security well enough to prevent them from making potentially
high-cost mistakes.  
Such mistakes include
accidentally deleting the private key,
accidentally publicizing a key, accidentally revoking a key,
forgetting the pass phrase, and failing to back up the key rings.</P
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gnupg-doc 2003.04.06+dak1-1ubuntu1 / usr / share / doc / gnupg-doc / GNU_Privacy_Handbook / html / c569.htm
