Myths of Password Security • Hacker News Board

Re: Myths of Password Security

#41

Post by jfarmer » Fri, May 03, 2013, 4:15 PM UTC

mistercow wrote: post #36

aiiane wrote: post #32

Earlier quoted context omitted.

That's a very binary way of looking at it. Depending on the sign up flow, it may be much more difficult to discover the existence of a username or not, than it is in the login form. (For instance, if the signup flow involves payment details before the username step.)

Are you going to enforce uniqueness of payment details? And if so, what part of those details must be unique? Will you require a unique credit card number? If so, you will have to maintain either a bloom filter or a list of hashes for all eternity to ensure that nobody signs up twice with the same CC number. [Edit: actually, you could keep the scrambled CC data for a finite length of time if you're just trying to rat…

If you're using a third-party payment provider like Authorize.net or Braintree to store CC numbers, you'll be given a unique token from the provider when you add the CC number. When you add the CC you can also have the provider run and immediately void a dummy transaction to verify the card is real, too.

Re: Myths of Password Security

#42

Post by venomsnake » Fri, May 03, 2013, 4:37 PM UTC

mistercow wrote: post #26

venomsnake wrote: post #25

Fist myth is that passwords provide security. The human brain is crappy rng so it cannot create proper high entropy passwords. No way getting around that - whatever your password is if it is "derived" from something - someone else is using it too. The only viable security I can think of is if we have distributed public key infrastructure. Bitcoin style wallets. And securing the "PK wallets" is up to the end user. Per…

>The human brain is crappy rng so it cannot create proper high entropy passwords. No way getting around that... Yes there is: you use a real RNG to generate your password. A good option is http://passphra.se . Just remember that you can't go clicking "Generate Another!" until you find something particularly memorable, or you'll be sacrificing an unknown amount of entropy by narrowing the space to memorable passwords.…

If we assume that English has 65535 words a four word password gives you 64 bits of entropy. Of course the real number of words that you can use for mass generation is 2k (or even less) if we search words that everyone that is standard deviation or two below the mean on the vocabulary graph can use and spell correctly. Spelling is going after the ability to memorize telephone numbers too with everyone using the crutches of autocorrect and other spell checking tools. The moment everyone uses that scheme the people interesting in reversing passwords will move in that direction too.

This is fake security trough obscurity. You can get pretty secure passwords nowadays by just concatenating your username and site domain and md5-ing them and taking the first half. It generates awesome passwords ... until you are the only one using this way of deriving passwords.

The human brain is not suited for remembering long complex passwords. Even less suited for unique for every service.

Re: Myths of Password Security

#43

Post by pizza » Fri, May 03, 2013, 4:40 PM UTC

I'd say jjjjjjjjjjjjjjjjjjjjjjjjjjjj, from a human-interpetation standpoint, has very low entropy, since there is very little uncertainty as to what will come next... This would be evident if password security checkers tried to compress passwords and compare them to the original message.

i.e. "jjjjjjjjjjjjjjjjjjjjjjjjjjjj" is 224 bits as a string. Huffman-encoded, you only need 0=j as a code to convert it into 28 bits, a compression of 87.5%. So this is a good way of actually checking the security of a password, if it seems to have high entropy.

Re: Myths of Password Security

#44

Post by aiiane » Fri, May 03, 2013, 4:47 PM UTC

mistercow wrote: post #36

aiiane wrote: post #32

Earlier quoted context omitted.

That's a very binary way of looking at it. Depending on the sign up flow, it may be much more difficult to discover the existence of a username or not, than it is in the login form. (For instance, if the signup flow involves payment details before the username step.)

Are you going to enforce uniqueness of payment details? And if so, what part of those details must be unique? Will you require a unique credit card number? If so, you will have to maintain either a bloom filter or a list of hashes for all eternity to ensure that nobody signs up twice with the same CC number. [Edit: actually, you could keep the scrambled CC data for a finite length of time if you're just trying to rat…

I was actually thinking of cases like MMO game accounts - often times the actual game account isn't created until after the game is purchased.

Re: Myths of Password Security

#45

Post by aiiane » Fri, May 03, 2013, 4:54 PM UTC

T-hawk wrote: post #38

aiiane wrote: post #34

Earlier quoted context omitted.

It actually wouldn't, because the entropy doesn't rely on the attacker not knowing the general format - it relies on the number of words available as choices.

English has roughly 100,000 words, so that password scheme has 10^15 combinations. Suppose the latter scheme incorporates the 96 printable Ascii characters. log96(10^15) is 7.5, so yes the latter scheme gets ahead on entropy at 8 characters or longer. But it's not a question of maximizing entropy. It's a question of maximizing entropy relative to the human brain's ability to remember it . The brain handles words as s…

I go by the xkcd standard of 4 words, though that doesn't change the math, just the numbers.

Re: Myths of Password Security

#46

Post by pfedor » Fri, May 03, 2013, 4:56 PM UTC

kijin wrote: post #24

geal wrote: post #13

Saying that using random words is better than using a string of unrelated characters assumes that password crackers don't know how to combine words. There are about 180000 words in English (but don't assume everybody knows 180000 words). That means that for three words, you have at most 5.8 10^15 options. For a password with mixed case and numbers, you have 62 different characters. With, 9 characters, you have 1.3 10…

It depends on how many words you have in a string. XKCD's oft-quoted comic uses 4 words. That would be 100000 times stronger than using just 3 words, and vastly superior to your example of a random 9-char password. The article's own example, "golf kangaroo crispy halitosis", also uses 4 words. I agree with you that long random passwords are the way to go, but even in that case you need to remember at least one passwo…

The problem is, if you actually choose your 4 words randomly out of the full dictionary, you won't get something like "golf kangaroo crispy halitosis" or "correct horse battery staple". It will sound closer to "capaciously endodermal remast amarantite". The set of words as familiar as "golf", "kangaroo", etc. is much smaller than 100k.

Re: Myths of Password Security

#47

Post by dllthomas » Fri, May 03, 2013, 4:57 PM UTC

eddiemunster666 wrote: post #21

pornel wrote: post #17

A myth I'd like to dispel is that when login fails not telling whether username or password was wrong improves anything. Please do tell clearly when username was wrong. It won't disclose anything new, because you're already disclosing this information by validating registration form (and reg form will even disclose existence of registered e-mails by forbidding duplicate registration), existence of profile URLs, all k…

I humbly disagree, if you say to the user that the username was correct but the password was wrong then you have leaked information to the user that they should not have access to. i.e. If email is used as a username and I go to a porn site and type in my wifes email address and a random email and it comes back 'username right, password wrong' then I now know she has an account there which she was trying to kepp secr…

Leaking emails is bad. Leaking site-specific user-names seems like less of an issue, particularly when they're exposed anyway through simple use of the site.

Re: Myths of Password Security

#48

Post by dllthomas » Fri, May 03, 2013, 5:06 PM UTC

pfedor wrote: post #46

kijin wrote: post #24

Earlier quoted context omitted.

It depends on how many words you have in a string. XKCD's oft-quoted comic uses 4 words. That would be 100000 times stronger than using just 3 words, and vastly superior to your example of a random 9-char password. The article's own example, "golf kangaroo crispy halitosis", also uses 4 words. I agree with you that long random passwords are the way to go, but even in that case you need to remember at least one passwo…

The problem is, if you actually choose your 4 words randomly out of the full dictionary, you won't get something like "golf kangaroo crispy halitosis" or "correct horse battery staple". It will sound closer to "capaciously endodermal remast amarantite". The set of words as familiar as "golf", "kangaroo", etc. is much smaller than 100k.

It doesn't have to be as memorable as kangaroo, it has to be more memorable than the equivalent (in entropy) number of random characters, which I think is basically any word.

$ wc -l /usr/share/dict/words

99171 /usr/share/dict/words

$ rl -c 4 /usr/share/dict/words | xargs -d\\n

contortionists mocking Alphard soling

$ rl -c 4 /usr/share/dict/words | xargs -d\\n

Toni's dish's mauled spillages

$ rl -c 4 /usr/share/dict/words | xargs -d\\n

expedited tireless interneships tranquiller

$ rl -c 4 /usr/share/dict/words | xargs -d\\n

bohemian rogering unkindliest ayes

Re: Myths of Password Security

#49

Post by mnarayan01 » Fri, May 03, 2013, 6:22 PM UTC

eterm wrote: post #35

mnarayan01 wrote: post #23

Earlier quoted context omitted.

Not to imply that what you describe is a great strategy, but I wouldn't describe it as pointless. The password "12345" has the same entropy as "b0g4p" but it would be a mistake to think they are equally secure.

Is bogap a dictionary word? What I'm describing are passwords like T1g3rF33t Cam3lT03 etc. All dictionary stuff along a theme, but made "secure" by applying a zero-entropy substitution of all occurrences of (L,O,A,E) with (1,0,4,3). Given that crackers know people do this, they add them to their dictionary attack routines so this is no more secure. Given I'm still fighting with them over, "don't store passwords plain…

Ha no...I just randomly typed in symbols. Guess it does look kind of "wordish" though.

Re: Myths of Password Security

#50

Post by mnarayan01 » Fri, May 03, 2013, 6:31 PM UTC

mistercow wrote: post #29

mnarayan01 wrote: post #23

Earlier quoted context omitted.

Not to imply that what you describe is a great strategy, but I wouldn't describe it as pointless. The password "12345" has the same entropy as "b0g4p" but it would be a mistake to think they are equally secure.

>The password "12345" has the same entropy as "b0g4p" but it would be a mistake to think they are equally secure. Those do not have remotely equal entropy.

At the byte level it does, which is presumably what the OP was talking about when saying that replacing characters with digits (uniformly) does not affect entropy.