[kadoban]

There's some things that are obviously bad: popular movie quotes, slightly less bad (but still bad): any quote from anything ever produced in any medium.

Some things that are obviously good (you can calculate the entropy easily): diceware style schemes, generated with dice or a secure random generator.

Anything in the middle it's quite hard to say. Humans are really bad at being random, so words you pick out of your head I'd be fairly suspicious of. But it's hard to prove it's a bad idea.

[sirsuki]

Considering length is key in computing “strength” I’m curious how using a long dialog from a movie might make it bad? Presuming you account for the full 95 entropy set (numbers, upper/lower letters, special characters) and padding¹ then how would an attacker know that a failed phrase failed because it was the wrong phase or because they forget to add some padding that is still unknown.

From a dictionary/rainbow table perspective I'm curious how they would know to include the following in their lookup tables before going fill number crunching mode:

  TO be or NOT two be - that is the question!!!!!!!!!!7872665398

Bitwarden suggests this is strong as does GRC Haystacks¹ thoughts?

¹ https://www.grc.com/haystacks.htm

² https://bitwarden.com/password-strength/

[kadoban]

The only entropy that has is:

1) the choice of quote. Say that's in the top ten quotes ever, so something like 3 or so bits of entropy.

2) the modifications and additions to the quote. Really depends what the scheme is, but few bits for which words are capitalized (~4), few bits for where the hyphen is (~3), few bits for how many bangs (~4), and a bunch of bits for which number goes on the end, (~30ish). Some bits to account for the scheme itself and its choices too, but I don't know how to put a number on that.

Do you see how little is actually coming from the quote? Your passphrase might as well just be "95!!!!78726653980" and if anything that's _easier_ to remember.

Compare against something like a diceware passphrase. _All_ of the entropy comes from the passphrase part, the part that's easy to remember and trivial to calculate how secure it is.

So a quote is bad because you can _make_ it secure, but you making it secure is just throwing crap at it until it's no longer functionally a quote in any real way. It's secure the same way a blank password is.

[tuhriel]

what I don't get with this argument, why does the quote only give 3 bits of entropy? Are the cracking algorithms so good that they know to try "or not to be" after they get to "to be". Also, as far as I remember you can't get a "you are partially there" result. Either you get the password or not. So they wouldn't know that "to be" are the first five chars.

Even for badly pw parts which could traced back to me. Let’s say I use my girlfriends name, surname and birthdate. If someone targets me directly, definitely a bad idea. For a random bruteforcer or even a dictionary attack with rockyou.txt, as an example, it wouldn't change a thing.

Or do I miss something here?

[kadoban]

> what I don't get with this argument, why does the quote only give 3 bits of entropy?

Good question. 3 bits is based on the part I mentioned where "to be or not to be" is one of the top 10 quotes. log(10) is about 3. The reasoning for this is that this quote is going to be in a "dictionary" your attacker has. 10 is probably a bit unfair on my part, because an attacker is probably really going to be guessing from a larger pool of quotes, but it ends up not mattering _too_ much. If their pool of quotes is 1000 long, that's more like 10 bits of entropy (still far, far too little on its own).

> Are the cracking algorithms so good that they know to try "or not to be" after they get to "to be". Also, as far as I remember you can't get a "you are partially there" result. Either you get the password or not. So they wouldn't know that "to be" are the first five chars.

Yeah, it's not based on anything like this. Assuming whoever implemented the password input (bitwarden in this case) isn't _maliciously_ incompetent, an attacker would get no information from a partially-correct password guess.

> Even for badly pw parts which could traced back to me. Let’s say I use my girlfriends name, surname and birthdate. If someone targets me directly, definitely a bad idea. For a random bruteforcer or even a dictionary attack with rockyou.txt, as an example, it wouldn't change a thing.

This is not completely wrong, but somewhat incomplete. Names and birthdates/years (or dates in general) are both really common parts of passwords. So an attacker will have a dictionary of common names (or ~all names, there's not that many of us), and every date that's possible to be important to someone.

So that already reduces the entropy a lot. And yeah it's bad enough if someone targets you directly that it's just a horrible idea.

The other problem with schemes like this: if you're using a password of that form, you're probably reusing it multiple places. This allows any site you have an account at to trivially access any _other_ place you have an account at. Really, really bad news.

[tuhriel]

Thanks for the clarification. I guess I somehow underestimated the extent of the dictionaries "available".

...and probably how they extend their search patterns.

P.s.: I wouldn't use the pattern in my example... :-)