[6990] in cryptography@c2.net mail archive
Re: Automatic passphrase generation
daemon@ATHENA.MIT.EDU (Steve Reid)
Wed May 3 00:33:04 2000
Date: Tue, 2 May 2000 17:14:13 -0700
From: Steve Reid <sreid@sea-to-sky.net>
To: Rick Smith <rick_smith@securecomputing.com>
Cc: coderpunks@toad.com, cryptography@c2.net
Message-ID: <20000502171413.A412@grok.localnet>
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In-Reply-To: <3.0.3.32.20000502101414.00ac7100@mailhost.sctc.com>; from Rick Smith on Tue, May 02, 2000 at 10:14:14AM -0500
On Tue, May 02, 2000 at 10:14:14AM -0500, Rick Smith wrote:
> Is it really necessary to protect against an attack that orders the phrases
> according to how easy they are to remember? Clearly, a practical brute
> force attack against the passphrases must be automated. But I don't know of
> an algorithm for assessing the "memorability" of a passphrase.
The obvious approach would be to start with the shortest, simplest,
and/or most common words first. This would try "the happy duck slowly
kisses the yellow book" before something like "the aboriginal physicist
chemically anodizes the artificial hypotenuse". I don't think it would
be difficult to quantify such things- if it's just done on a per-word
basis it could be done by hand.
There are bound to be more sophisticated methods. If someone needs to
brute force passphrases with lots of entropy, it may well be worthwhile
to spend a lot of time and money studying what makes a passphrase
desirable. If it means that the number of passphrases that need to be
tried can be reduced by a factor of several then it may make the process
significantly more cost-effective.
