PGP and dictionary attacks on private secret keyring

Hi all

I'm studiing the PGP (and GPG) documentation. As known, one of the major
(and known, of course) risk is a dictionary attack on a (stolen) private
secret keyring. Everywhere is written, that this type of attack is very
easy to do (is somebody get my keyring) but I can't find any documents
about this type of attack.

I have the GPG sources, but this didn't help me. Can anybody send me a
link to this type of documentation?

Thanks
Michal

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Michal Vymazal
vymazal at secunet dot cz