Entropy isn't sufficient to measure password strength
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Re: Entropy isn't sufficient to measure password strength
#2Maybe I just don't have trendy-enough coworkers or friends...but I know of no one who actually analyzes password strength in terms of Shannon entropy. Cripes, the very first sentence of the Wikipedia page for Shannon entropy tells us that it's an average.
Simple analogy - if the goal was to protect your house from a 9-foot-deep flood, would a dike with an average height of 10 feet do the job?
Re: Entropy isn't sufficient to measure password strength
#3The real question here is if there are any actually used password strategies where this distinction matters? In practice, no one would ever use the type of password strategy described.
Re: Entropy isn't sufficient to measure password strength
#4Kolmogorov complexity/entropy is more suitable for this purpose, under the implicit assumption that password crackers don't have tailored prior knowledge and are just enumerating "simple" sequences. It only agrees with Shannon entropy on long ergodic sequences. The author basically constructed an example where the two notions don't agree.
Re: Entropy isn't sufficient to measure password strength
#5Re: Entropy isn't sufficient to measure password strength
#6Maybe I just don't have trendy-enough coworkers or friends...but I know of no one who actually analyzes password strength in terms of Shannon entropy. Cripes, the very first sentence of the Wikipedia page for Shannon entropy tells us that it's an average . Simple analogy - if the goal was to protect your house from a 9-foot-deep flood, would a dike with an average height of 10 feet do the job?
Yep one of those cases, where an ensemble average is not at all relevant for describing the situation.
Re: Entropy isn't sufficient to measure password strength
#7Maybe I just don't have trendy-enough coworkers or friends...but I know of no one who actually analyzes password strength in terms of Shannon entropy. Cripes, the very first sentence of the Wikipedia page for Shannon entropy tells us that it's an average . Simple analogy - if the goal was to protect your house from a 9-foot-deep flood, would a dike with an average height of 10 feet do the job?
I've done a fair bit of research into this, and as far as I can tell, the entire internet does this thing you've never seen. For example, https://en.wikipedia.org/wiki/Password_strength#Entropy_as_a... implies the use of Shannon entropy.
Re: Entropy isn't sufficient to measure password strength
#8There's a bit of a logical flaw here in that the argument is made against average entropy of a set of passwords, rather than individual entropy of each chosen password.
This is an argument I can't find anyone making: an aggregate average entropy of the set of all passwords you use is fine for password security, rather than the entropy of each individual password.
As far as I can tell this seems to be a (possibly intentional?) misunderstanding on the author's part.
Re: Entropy isn't sufficient to measure password strength
#9It’s important to remember that attackers get no information on how close they are (assuming good hashing practices). It is unknowable to them if you went with the correcthorsebatterystaple approach or placed your cat on the keyboard for a few minutes. Given that, a simpler alphabet with longer strings > more complexity with shorter strings.
Re: Entropy isn't sufficient to measure password strength
#10The real question here is if there are any actually used password strategies where this distinction matters? In practice, no one would ever use the type of password strategy described.
This is a fair question; I've been thinking about "weird" password choice strategies recently, for which it can matter. For example, if you want your password to be an English sentence, choosing sentences based on random parse trees will produce duplicated sentences with ambiguous parses.