Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

How crackers ransack passwords like “qeadzcwrsfxv1331”

arstechnica.com

Post reply on HN
Print view View original

21–30 of 123 posts

Re: How crackers ransack passwords like “qeadzcwrsfxv1331”

#21

Post by chm »

tomku wrote: post #19
chm wrote: post #8

Earlier quoted context omitted.

But doesn't this render the process useless? If an attacker gets access to the hashes, he also gets access to the salts. If both hashes and salts were isolated, I suppose it would be much more secure, although maybe too slow.

Absolutely not. Like I said, the point of the salt is not to provide a "second password" that needs to be independently stolen. It's to make the results from a cracking attempt on one account useless on the password of another. If you've read the article, you have a pretty good idea of how it works without salting. You have a list of N password hashes, and you come up with candidate passwords. You run each candidate…

That's what I understood from the article, and why I suggested the salts and hashes should be handled separately.

If you give the attacker the salts, difficulty scales linearly. For two identical plaintexts, all that differs is the salt, but it is given to him.

If you store the hashes and salts separately (the technical details of which I know nothing about), then you augment the keyspace exponentially. For N byte salts, using P characters, you augment it by N^P. Furthermore, who forces you to append a salt? You could prepend. Or n-pend.

I'm just throwing ideas around.

Re: How crackers ransack passwords like “qeadzcwrsfxv1331”

#22

Post by tomku »

lbarrow wrote: post #15
tomku wrote: post #3

Enjoyable read, but I question the bit near the end claiming that salts wouldn't help much against this kind of attack. From my understanding, per-user salting does substantially slow down this kind of attack because it forces you to calculate a different hash for each user/plaintext combination rather than hashing a suspected plaintext once and comparing the hash against the whole list. What it doesn't slow down is…

The article clearly explained that using more salts was preferable to using a global salt and did a good job of explaining why. They didn't come out and say that a per-user salt is best, but that's the natural conclusion of the argument they developed.

Maybe we read different articles, but the one I read seemed intent on strongly downplaying the amount of extra security that salting provides. It actually uses the phrase "minimal amount of protection" to describe a salt's effect on cracking attempts.

That seems like a strange choice of words when salting would've completely changed the outcome of the cracking attempts described in the article.

Edit: To be clear, I'm aware that salting doesn't protect against targeted attacks, but the attacks discussed in the article weren't targeted. One of the major reasons[1] they were able to crack 16,000 passwords in a few hours was due to the lack of salting.

[1]: The other being the choice of MD5 rather than bcrypt/scrypt/PBKDF2/etc, naturally.

Re: How crackers ransack passwords like “qeadzcwrsfxv1331”

#23

Post by nknighthb »

chm wrote: post #21
tomku wrote: post #19

Earlier quoted context omitted.

Absolutely not. Like I said, the point of the salt is not to provide a "second password" that needs to be independently stolen. It's to make the results from a cracking attempt on one account useless on the password of another. If you've read the article, you have a pretty good idea of how it works without salting. You have a list of N password hashes, and you come up with candidate passwords. You run each candidate…

That's what I understood from the article, and why I suggested the salts and hashes should be handled separately. If you give the attacker the salts, difficulty scales linearly. For two identical plaintexts, all that differs is the salt, but it is given to him. If you store the hashes and salts separately (the technical details of which I know nothing about), then you augment the keyspace exponentially. For N byte sa…

The server must have access to both the salt and the hash to verify a password. Therefore, upon compromise of the server, the attacker automatically has access to both the salt and the hash. There is no way around this problem that isn't simply obfuscation.

Re: How crackers ransack passwords like “qeadzcwrsfxv1331”

#25

Post by jacques_chester »

talloaktrees wrote: post #24

I don't know too much about crypto. Would using something like salsa20 stop this?

A password-derivation function has two requirements:

1. Obscure the password in a one-way fashion.

2. Be fast enough for humans, but very slow in computer time.

Hash functions can be used to produce an obscured copy of data, but they are also by design very fast.

If you wish to protect passwords, don't use a naked hash algorithm. Choosing a different hash algorithm doesn't fix the problem.

Instead, use a password-derivation function. These are designed both to obscure and to take significant time. Bcrypt, Scrypt and PBKDF2 are the standards.

Re: How crackers ransack passwords like “qeadzcwrsfxv1331”

#26

Post by jevin »

grecy wrote: post #5
jacques_chester wrote: post #2

The punchline: > The list contained 16,449 passwords converted into hashes using the MD5 cryptographic hash function. Edit: I'm removing all my snarky nitpicking. This is a good article. Yes, the MD5 case they present is a poor case, but it's really about demonstrating the tactics of attack selection, rather than teaching someone how to make crack-resistant password schemes.

> the MD5 case they present is a poor case If guys using vanilla hardware get that kind of success in 1 hour with MD5, you only need to increase hardware and the time required to see it's still completely doable for other hash functions.

That's why the Blowfish algorithm is the best choice for password hashing.

The algorithm uses CPU cycles to generate the hash. So there is no way to speed it up, just by using a faster computer.

Re: How crackers ransack passwords like “qeadzcwrsfxv1331”

#28

Post by jd007 »

The article explains how all the passwords were revealed except for "qeadzcwrsfxv1331". Maybe I missed it but could anybody point out to me which method revealed this password? The letters seem to not form any words that I know, and although is appended with a number and consists of only lower case letters, it's still 12-letters long, longer than any brute-forced in the article. Edit: They tried all the keyboard typing patterns I suppose, I just realized the pattern of the string when typed on the keyboard.

Re: How crackers ransack passwords like “qeadzcwrsfxv1331”

#29

Post by kenbot »

jd007 wrote: post #28

The article explains how all the passwords were revealed except for "qeadzcwrsfxv1331". Maybe I missed it but could anybody point out to me which method revealed this password? The letters seem to not form any words that I know, and although is appended with a number and consists of only lower case letters, it's still 12-letters long, longer than any brute-forced in the article. Edit: They tried all the keyboard typi…

Try looking at the pattern the letters form on the keyboard...

Re: How crackers ransack passwords like “qeadzcwrsfxv1331”

#30

Post by jd007 »

kenbot wrote: post #29
jd007 wrote: post #28

The article explains how all the passwords were revealed except for "qeadzcwrsfxv1331". Maybe I missed it but could anybody point out to me which method revealed this password? The letters seem to not form any words that I know, and although is appended with a number and consists of only lower case letters, it's still 12-letters long, longer than any brute-forced in the article. Edit: They tried all the keyboard typi…

Try looking at the pattern the letters form on the keyboard...

Yeah thanks, I literally realized that as I hit reply on that comment lol
Post reply on HN