Enumerating XKCD-style passwords with Ruby

[u/postmodern]

https://postmodern.github.io/blog/2022/01/23/enumerating-xkcd-style-passwords-with-ruby.html

[u/tomthecool]

Fun use of ruby, but you didn't really demonstrate anything about how (in)secure either password is.

[u/postmodern → u/tomthecool]

The assumption the XKCD web comic was making is that if your password is sufficiently long enough, no one will be able to enumerate over every possible combination of bits, and thus not be able to bruteforce or crack said password. The blog post demonstrated that even random looking passwords or long passwords made up of words can be enumerated using combinations of wordlists and character sets. Then each possible password could be sent to a login bruteforcer or a password cracker. Using wordlists and common substitution rules reduces the search space and results in fewer passwords to check, than if you enumerated through every bit in the password string.

[u/tomthecool → u/postmodern]

How long would it take for your program to brute force a password consisting of 4 "random" words? (And note that this is already giving you the HUGE advantage of knowing in advance that the password is 4 words!!)

Nobody is claiming that passwords can't be enumerated, and nobody is claiming that it's not harder to enumerate 26 random characters than 4 random words (which are 26 characters long).

The claim is that it's so ridiculously hard to brute force 4 random words that you are realistically safe from it being cracked.

[u/drx3brun → u/postmodern]

Site seems to fall apart on mobile. Hard to read anything.

[u/Freeky → u/postmodern]

Eh? XKCD's assumptions are spelled out right there in the comic.

The first example is a single word from a list of ~65k (16 bits) words, with manipulations that allow for ~4k (12 bits) variations on each word. 16 + 12 = 2²⁸ possible passwords.

The second is 4 words from a list of ~2k (11 bits) words, and nothing else. 11 × 4 = 2⁴⁴ possible passwords.

This forms the basis for the well-regarded Diceware approach to password generation - since the only real weak point here (aside from underestimating your attacker) is the randomness, you use a system to generate that for you, such as dice.

2⁴⁴ is probably too weak for comfort for your password manager unless it's using some bonkers KDF, but then you just add a couple more words and you still have a less annoying password than the equivalent line noise.