Legal compulsion and self-incriminating passphrase

[Caspar Bowden]

An interesting point on these issues is raised (in the US context) in:
http://www.urich.edu/~jolt/v2i1/sergienko.html

"A cryptographic key need not have testimonial content. A key can be any
word, phrase, or a series of randomly chosen digits. However, one can
imagine a cryptographic key that has been given an incriminating,
testimonial content by making it a word or phrase that confesses to a crime.
Many seldom-enforced statutes[16] enable one to confess to a crime in one's
cryptographic key, thereby triggering potential criminal liability and
therefore the protection of the Fifth Amendment"

If it is the case (or claimed by the defendant) that the passphrase is a
(true) confession to a crime, would this invoke any protection against
self-incrimination under UK law? The difficult case is when the crime of
which the prosecution seeks evidence in the encrypted data, is much more
serious than the crime confessed to in the passphrase (e.g. "I dropped
litter in Trafalgar Square on dd/mm/yy").

Does the relative seriousness of the crimes make any difference ?
--
Caspar Bowden
Director, Foundation for Information Policy Research
Tel: +44(0)171 354 2333
Fax: +44(0)171 827 6534