50 characters ? (was RE: Man jailed over computer password refusal

[James Firth]

> Not really relevant but I think I could remember a 40-50
> character password if it was derivable from a poem or a song or
> similar, or if it was mostly dictionary words.

On the crypto angle NIST recons the entropy in English language passphrases
is so low that one needs over 50 characters to achieve 80-bit equivalent key
strength.

http://csrc.nist.gov/publications/nistpubs/800-63/SP800-63V1_0_2.pdf

Of course the entropy significantly increases if one uses random
capitalisation and illogical placing of alphanumerical characters, which
then somewhat obviously can make the passphrase less memorable.

James Firth