Saturday, October 13, 2007

Rant: Passphrases Continued -- Why They Haven't Caught On?

In a previous article I talked about passwords vs. passphrases, and why, in general, randomly generated passphrases are a better idea than passwords. But while discussing my results with others the question came up "if they are so cool, why haven't they caught on?"

I think there are several reasons for that. One of which is that, historically speaking, space was limited, so passwords couldn't be longer than 8 characters. Thus password culture has been built around an eight-character password, even though this limitation has disappeared from pretty much every system.

But I think the main reason is that they just don't feel secure.

Think about it. Which one feels more secure to you? Opjk8J2Q or PiecesStudySmoothCatch? With all the security experts always telling you that you need a password with symbols and numbers in it, while avoiding dictionary words, passphrases seem to go against everything we've been told!

But as my article showed, a random four-word passphrase that is generated from a dictionary of only about 4000 words is just as difficult to crack as a random 8-character password made of alphanumeric characters! Indeed, if the exact dictionary of words you are using for password generation is unknown by an attacker, it becomes even more secure, as they have to try passphrases with words that have no relevance to your system.

A Little Extra

While I'm here I do want to mention two extra thoughts that came up while discussing my previous article with others.

The first thing is that passphrases are really no good if people can choose their own, as people are likely to choose certain words more over others. This uneven distribution could be figured out through simple studies and then exploited by an attacker.

On the other hand a random passphrase is so much easier for someone to remember that with a secure situation, issuing passphrases that people cannot change will work out better than issuing random passwords (since people usually have to write down random password, creating a place to breach security by a spying party; e.g. a janitor) while being more secure than a password that someone chooses for themselves.

Remember, depending on the system, it only takes one weak password for an attacker to hack into a system and get access to password information to start doing brute-force attacks on administrator passwords!

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