3 ms·

Eight characters for a password seems plenty long to me, if you're truly using a random password. You have [A-Za-z] = 52 chars, [0-9] = 10, [!@#$%^&()_-+=;':",.

by ihodes 15y ago

Eight characters for a password seems plenty long to me, if you're truly using a random password. You have [A-Za-z] = 52 chars, [0-9] = 10, [!@#$%^&()_-+=;':",.<>/?\|[]{}] = 30, for a total of 92 possibilities. Then you have an 8 character password. Even if the attacker knows you're using 8 characters, you've got ((92^8)0.3)/60/60/60/24/365/100 = 271 centuries if it takes 0.01 seconds a try. And we're really talking over 8 thousand centuries if we're having bcrypt take 0.3 seconds. So the problem is that passwords tend not to be random. This greatly decreases the problem-space. But b/scrypt solves the problem of length, within reason.

vog 15y ago
I fully agree, but I'd focus more on the length than on the character set. It is not a problem if the password contains only alphanum characters, as long as those are random. For instance, a plain alphanum password of length 9 is stronger than a password of length 8 that allows for special characters. (because 62^9 > 94^8) In other words, adding one character to your password is as good as choosing from a bigger character set. Okay, beginning at length 10, you'd need to add two characters, but that's really all you need to do up to length 20. (which is an insane length for a random password anyway)
- Jach 15y ago
  C^x grows a lot faster than x^C, except for specific x's and C's you're almost always much better off adding to the length. And 20's nuttin'. At the risk of publishing more hastily written code for critiquing, here's a shell script password generator I use sometimes. https://gist.github.com/1058565 https://gist.github.com/1058565
lloeki 15y ago
Yet with just [A-Za-z] and 10 random chars you're at 52^10 ~ 1E17 while your wider choice set gives 92^8 ~ 1E15, so ten random alpha chars is really better than ten alpha+number+punctuation. Suddenly it takes a paltry 229 thousand centuries (or 22 million years) with bcrypt at 0.3s. Using punctuation does not make a password "more random", it only makes the random choice set slightly larger. Bumping the length is much more significant than bumping the set as it's exponential. The debate is whether it's easier for a user to both pick and remember a "random-enough" - i.e not easily bruteforce-able, regardless of hashing technology - [A-Za-z]{10} password or a [A-Za-z0-9!@#$%^&()_-+=;':",.<>/?\|[\]{}]{8} password. For the record, Google's 2-factor auth generated app-specific passwords are [a-z]{16}, which gives 1E22, or 230 billion years with bcrypt at 0.3s.
cperciva 15y ago
With $10k of GPUs, you can compute an MD5 hash for every 8-character ASCII printable password (yes, all 95^8 of them) in under a day. This is why MD5 is not a good password-based key derivation function. :-)

by ihodes 15y ago

vog 15y ago

I fully agree, but I'd focus more on the length than on the character set. It is not a problem if the password contains only alphanum characters, as long as those are random. For instance, a plain alphanum password of length 9 is stronger than a password of length 8 that allows for special characters. (because 62^9 > 94^8) In other words, adding one character to your password is as good as choosing from a bigger character set. Okay, beginning at length 10, you'd need to add two characters, but that's really all you need to do up to length 20. (which is an insane length for a random password anyway)

Jach 15y ago
C^x grows a lot faster than x^C, except for specific x's and C's you're almost always much better off adding to the length. And 20's nuttin'. At the risk of publishing more hastily written code for critiquing, here's a shell script password generator I use sometimes. https://gist.github.com/1058565 https://gist.github.com/1058565

lloeki 15y ago

Yet with just [A-Za-z] and 10 random chars you're at 52^10 ~ 1E17 while your wider choice set gives 92^8 ~ 1E15, so ten random alpha chars is really better than ten alpha+number+punctuation. Suddenly it takes a paltry 229 thousand centuries (or 22 million years) with bcrypt at 0.3s. Using punctuation does not make a password "more random", it only makes the random choice set slightly larger. Bumping the length is much more significant than bumping the set as it's exponential. The debate is whether it's easier for a user to both pick and remember a "random-enough" - i.e not easily bruteforce-able, regardless of hashing technology - [A-Za-z]{10} password or a [A-Za-z0-9!@#$%^&()_-+=;':",.<>/?\|[\]{}]{8} password. For the record, Google's 2-factor auth generated app-specific passwords are [a-z]{16}, which gives 1E22, or 230 billion years with bcrypt at 0.3s.

cperciva 15y ago

With $10k of GPUs, you can compute an MD5 hash for every 8-character ASCII printable password (yes, all 95^8 of them) in under a day. This is why MD5 is not a good password-based key derivation function. :-)