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Coding Horror: You're Probably Storing Passwords Incorrectly
- chmac 19y agoGreat article, some good links, and a damned eye opener. I need to start salting my passwords...
- brlewis 19y agoI need to start using a longer salt and/or a slower hash.
- mynameishere 19y agoAnd I need to come up with a website worthy of someone breaking into.
- adamdoupe 19y agoSo much to do, so little time.
- thomasptacek 19y agoSalt length and hash speed are orthogonal. Increasing the length of your nonces doesn't make your passwords less crackable. If this is news to you, don't design your own password scheme; use someone else's good one, so you aren't accidentally exposing people's bank accounts.
- aston 19y agoIncreasing the length of the nonce definitely makes the password less crackable. Since brute force methods search the entire space, the more space, the better. It's still possible to crack in by finding a hash collision, but the longer your non-password trash, the harder it is to recover the password via brute force.
- thomasptacek 19y agoAll due respect, but you shouldn't be designing password schemes. Modern password schemes are cracked using incremental crackers. This "rainbow table" stuff has totally confused the developer community. John the Ripper doesn't make a time/space tradeoff; it uses the (public) salt and the hash and iteratively recomputes hashes, and it is terrifyingly fast even on good password schemes.
- aston 19y agoThat's one attack vector. Assuming someone does attempt to use a brute force method, longer salts do matter. I think that qualifies as non-orthogonal to "crackability," even if orthogonal in some cases. Truthfully, this isn't even worth talking about. If your user's passwords are compromised, you've already lost the security battle. Hopefully you weren't actually storing something important.
- thomasptacek 19y agoThat's horribly irresponsible. Using your logic, you might as well just store the passwords in plaintext. Most people don't use different passwords for different applications, and your web application is inevitably going to expose all your users passwords, like every other web app that has been SQL-injectable (ie, almost all of them).
- aston 19y agoAs a person interested in security, you're well-familiar with the fact that nothing is 100% secure. Choosing a less secure option over a more secure one is not tantamount to choosing no security at all. That said, I personally don't mind plaintext passwords if there's a good usability story that goes along with it and if the security tradeoff is negligible. I put the odds of my user database being exposed at approximately zero, so generally it's a fine design decision. When was the last time you heard of passwords being stolen en masse from a major site that didn't also include a hard drive being stolen?
- deleted 19y ago[deleted]
- brlewis 19y agoAre you saying that nobody uses hash dictionaries anymore and one need only worry about brute-forcing of individual passwords? I'm not ready to stop thinking about hash dictionaries, and the 4-character salt I prepend to passwords before hashing is too short. A 4-character salt plus a 7-character password is a value that could be vulnerable to dictionaries roughly the size of the Rainbow tables. But if you can cite a paper demonstrating that brute-force cracks of individual passwords are the only thing one need be concerned about, I'll look at it and see if it changes my mind.
- thomasptacek 19y agoNobody is saying you don't need to use salted passwords. What we're saying is, if your password scheme is (user, nonce, SHA1(nonce, password)), don't bother; just store your passwords in plaintext. Your users passwords are so weak (dictionary word + number) that a 200 line incremental cracker is going to blaze through it in hours. The answer to this is to use someone else's (good) password scheme. If you're shipping on Unix, your system undoubtedly comes with one. Use it.
- brlewis 19y agoIf you mean to say that users should be forced to choose strong passwords, that's a different thing from saying longer salts don't make a set of passwords less crackable.
- thomasptacek 19y agoI don't understand why people are hyper-focusing on this one attack. Attackers have been cracking passwords, quite effectively, long before tools like Ophcrack were available. Any decent salt scheme beats Ophcrack; it doesn't take much to make hash chain storage infeasible. But you can make your salts longer than JSESSIONID's and they still won't be a speed bump to a "conventional" password cracker. I'm not arguing that users should be forced to choose secure passwords. They should, of course, but we're talking about how you store them. If you store them using a single-iteration SHA1 hash, then no matter how you structure your nonces, your scheme is insecure and you should be embarassed.
- thomasptacek 19y agoIf you have to reason through or alter what you're currently doing with passwords, it's irresponsible of you to be storing passwords at all. Like it or not, your users are using the same password for your web 2.0 recipe sharing program as they are for their bank account. Lesson: use someone else's (good) password system.
- aston 19y agoIf your bank only uses a username/password combo to confirm your identity online, you need a new bank.
- thomasptacek 19y agoIf you use the same password for your web 2.0 recipe account as your bank, etc, etc, etc. We shouldn't rationalize this stuff. All I'm saying is, don't make mistakes with your password system; use someone else's (good) password scheme.
- deleted 19y ago[deleted]
- davidw 19y ago> Lesson: use someone else's (good) password system. Ok, what? I use Ruby on Rails, and I want something open source. What do you recommend?
- thomasptacek 19y agoActs_as_authentable uses bcrypt.
- gwenhwyfaer 19y agoIs there a list of these somewhere? Which ones would you recommend?
- thomasptacek 19y ago
- henning 19y ago"most users tend to re-use the same passwords, probably because they can't remember the two dozen unique usernames and passwords they're forced to have. So if you obtain their forum password, it's likely you also have the password to something a lot more dangerous: their online banking and PayPal." I admit to being somewhat guilty of this, but I'm astonished anyone would use the same password for throwaway email acconts as for financial stuff. I do use only like 2 different passwords for all my stupid little Internet forum accounts, though.
- Readmore 19y agoSeriously, people store plain-text passwords? Come on guys, surely you know better than that!
- gscott 19y agoWith the exception of the database or backup being 'stolen' wouldn't the addition of a 3rd variable, like a captcha code, solve brute force attacks? I have been considering implementing something like a captcha code on my login forms (but haven't yet).
- jsjenkins168 19y agoServices like CAPTCHA are intended to solve different problems, like protecting your web service against DoS or bot/spam attacks. To brute force crack a password, you would really need direct access to the digest. We are talking around the order of 2^80 attempts before finding a collision with a algorithm like SHA-1. Checks need to happen very fast. Doing this through a web interface is already too slow to be feasible from a time perspective. So really, cracking passwords is only a consideration when someone gets a hold of all your digests (eg. your database) and can crunch away on them locally for a long time.
- thomasptacek 19y agoI'm really not sure you're talking about the same thing as, well, anybody else doing password security. Brute force incremental crackers (read: almost every password cracker ever written) don't attack the algorithmic strength of SHA1. They attack the complexity of the underlying passwords, using dictionaries, mutation functions, and statistics. SHA1 is strong (at least in this application). Passwords are very, very weak.
- thomasptacek 19y agoPassword cracking is an offline attack. If you think the only way you're going to lose your password table is if someone steals a hard drive or a backup, or uses a zero-day to root your whole server, you are making an extemely bad assumption.
- gscott 19y agoAssuming the webserver is not compromised, the sql server is on it's own local network, and the webserver is on both the local network and the Internet accessable network (2 network cards), how exactly does someone get direct access to the sql server to run an offline attack. I have always assumed the database server is safe there alone on it's own network as long as someone doesn't break into a machine that is connected to that network.
- jamongkad 19y agoGood thing I hash my passwords.
- joe 19y agoNo sir. I be using SHA256 hashes and per-password salts, ever since our site's launch.
- ivankirigin 19y agoDjango's session/user framework uses a salted hash. Does anyone have any critiques of their method?