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Comment by eps | Hacker News Reader

Instead of requiring 12+ char passwords with special symbols and driving people mad, require a long passphrase.

Everyone knows a verse from a song or a passage from a book and most people now have decent typing speed when it comes to text without $#^& and mixed case. So it's as fast to enter, much easier to recall and has a higher entropy even for phrases that aren't excessively long.

The ballpark estimate of the entropy of English test is between 1.0 and 1.9 bits per character, e.g. see [0]. This means that even a short passphrase like this:

  And I thought passwords were the best option.

would have between 40 and 80 bits of entropy.

[0] https://www.sciencedirect.com/science/article/pii/0960077994...

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Except that then you have a list of common phrases that you can check.

How many passpharses would be: "in god we trust" or "I love you". Figure out song titles and book titles, and you have a great list to check.

Clearly the minimum length restrition should still be there and be reasonably high, so none of these would qualify.

Your "see also" is about "multiword passwords", which is not the same.

My phones auto-complete shows how predictable English is. Lets start by guessing "And".

I see predictions: lastly also I

Let's pick "I".

Next I see: will believe am

If type "t" I get: think thought.

Let's pick "thought"

Next I see: I you it

I'll help it out and enter passwords.

Next I see: was would were

Let's pick "were". Etc.

A passphrase containing the word "password(s)" seems like an easy thing to guess especially given how popular "password" is as a password. Use of "thought" vs. "believe(d)" may just be my preference (curious if others see "thought" as a prediction).

I suspect if you had a sample of my writing, you could learn my word preferences and prioritize words I regularly use. I'm seeing half the words in auto-complete's first three guesses. Most of the rest are synonyms of a top three guess. Only the word "passwords" broke that pattern. I wouldn't recommend such a predictable passphrase like that.

You can not just look at a secret post-facto to reliabibly evaluate its strength, you have to include the process that was used to create the secret. And humans are notoriously bad at being RNGs, so anything chosen by a person is intrinsically weak as a secret.

> Everyone knows a verse from a song or a passage from a book

These do definitely don't have the 1.0 to 1.9 bits of entropy the paper you posted is talking about.

If what you're suggesting were to be "best practice" attackers would try, say, the 1 million most famous songs and the 1 million most famous books and take every sentence/verse from, say, the starting word of every sentence/verse up to 3 to 8 words.

This would be, what, very ballpark, a 34 to 36 bits keyspace?

Known text doesn't make for a good passphrase source.

How many words is that passphrase actually choosing from? Maybe 200? Three of them are "and", "the" and "I" which would probably be among the top 10 words used in a pass phrase.

In practice, pass phrases probably work well right now because they aren't used much, but if they were more commonly used and thus specifically attacked against, you would need passphrase strength rules.

A rule I use is to include a word that is not in a standard dictionary.

Just to mention, 200 choose 8 is roughly 10e14. If you could assuming 3 of the words are "and", "the" and "I", you limit the other word selection to 200 choose 5 ~= 10e10. Add an extra order of 4-5 for word order, and it's not like this is a small solution space.

But a randomly generated 9 character password is still stronger. There is a big over-confidence in pass phrases. As pointed out by other comments there is a predictible ordering to words in a passphrase. If you slip up like the parent commenter you end up with something that is actually weak. Pass phrases need rules (like requiring a non-dicitionary word).

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