encrypting files with lots of different keys

[Perry E. Metzger]

Jonathan Thornburg <jthorn at aei.mpg.de> writes:
> A further point:  Do you really want the granularity of your encryption
> to be "one key per disk"?  I much prefer a cryptographic file system
> which lets me have separate keys for separate categories of information
> (eg one key for my tax forms, a different key for company-confidential
> project stuff, a different key for old love letters, still another one
> for My Secret Plan For World Domination, etc etc).  These might all
> live on the same laptop, but they probably need quite different key
> policies.

I think that usability would make any such scheme outright
impractical. People can't keep track of one key -- keeping track of a
dozen would be rather difficult. Perhaps there are marginal benefits
to being able to use different policies for different parts of the
system, but it seems to me that the problems would far outweigh any
benefits. This is doubly true in a single user environment where there
is no issue with different subsets of users needing to see different
subsets of the data.

It is far simpler to simply use whatever key refreshment policy makes
sense for the most secure information on the file system and to use
one key. A system that is actually used beats a "better" system that
is never used every time.

Perry

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