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Ask HN: Which login method do you use?

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Re: Ask HN: Which login method do you use?

#51

Post by thorax »

tptacek wrote: post #33
thorax wrote: post #31

Earlier quoted context omitted.

I upvoted you because that's a good link and good advice in a sense. I don't agree fully with your exact phrasing and would put it a bit milder for someone asking this kind of question. I'd personally advise: Use a respected library or at least an MD5 or SHA1 approach with a strong salt. There are better ways that you should consider (link), especially if you're writing an authentication package for reuse by others.

It's painful to see someone recommend "at least" MD5+salt, when that solution is a single for() loop away from being at least adequate. If you're wondering why I'm using such strong words, it's because you talked about "strong salt" (which means nothing), but ignored stretching, which actually does improve security. SHA1+"strong salt" is extremely weak. It mitigates only one attack, which every respected authenticati…

Your article is great advice. As I worded it, I'm providing practical advice to a new web developer. Let me elaborate on my position:

First and foremost, don't write the password handling yourself if you can avoid it. If you do it yourself, I'm only firing the developers who put the password in plain text, and I'm not even going to give grief to the ones who at least use a rainbow-dodging salt and hash (like what most major web frameworks include by default for user auth management). I.e., if they use django defaults or Code Igniter defaults, then they're not in trouble.

Any senior engineers on the team are going to get some whining from me if the framework supports crypt/bcrypt and they didn't enable that, but if they forgot and the site launched without it, I'm not going to die.

It the team is making an authentication package for a web framework or especially for a native framework, they need to consider heavily using bcrypt (or other state-of-the-art approaches) for password handling unless there's some major compelling reason we cannot or should not.

What I'm trying to be is realistic and give the guy a side that's non-religious.

I agree with you as a hacker, but on the practical side, no coding decision is all-or-nothing with me.

If you're a new developer and have read this far and want to know where to find decent bcrypt packages for your favorite language, Google's AWT page has a good explanation and handy links to those (scroll down):

http://code.google.com/p/google-web-toolkit-incubator/wiki/L...

Also here's instructions for using crypt with Django auth:

http://docs.djangoproject.com/en/dev/topics/auth/#changing-p...

Re: Ask HN: Which login method do you use?

#52

Post by tptacek »

lsc wrote: post #49
decode wrote: post #47

Earlier quoted context omitted.

On average, the attacker will have to search half of the hash space to find a given password. So, your 40,000 searches is way too small as long as you require more than 2 character passwords. If you assume lowercase + uppercase + numbers for the passwords, and require at least 6 characters, you get (26 + 26 + 10) ^ 6 = 56,800,235,584 combinations searching half of that would be about 28 billion combinations. At 50ms…

if passwords are randomly generated, I agree with you completely, and everything I've said is crazy talk. But most passwords are not randomly generated. Most passwords are dictionary words, or two dictionary words. You don't need to search the hash space; you only need to search the password space, and if everyone uses the name of their dog, well, that's not a very large space. http://www.schneier.com/blog/archives/2…

If passwords are two dictionary words, then even with the system dictionary, a single 50ms hash takes 889,251 hours to crack. 8 million if people put a single digit at the end of it. You won't win this argument.

Re: Ask HN: Which login method do you use?

#53

Post by tptacek »

thorax wrote: post #51
tptacek wrote: post #33

Earlier quoted context omitted.

It's painful to see someone recommend "at least" MD5+salt, when that solution is a single for() loop away from being at least adequate. If you're wondering why I'm using such strong words, it's because you talked about "strong salt" (which means nothing), but ignored stretching, which actually does improve security. SHA1+"strong salt" is extremely weak. It mitigates only one attack, which every respected authenticati…

Your article is great advice. As I worded it, I'm providing practical advice to a new web developer. Let me elaborate on my position: First and foremost, don't write the password handling yourself if you can avoid it. If you do it yourself, I'm only firing the developers who put the password in plain text, and I'm not even going to give grief to the ones who at least use a rainbow-dodging salt and hash (like what mos…

Two responses.

First, we don't have pages and pages of comments and discussions because the topic isn't cut-and-dry. The topic is cut-and-dry. It just takes 5-10 round trips to explain to someone why clientside Javascript crypto is a bad idea.

Second, I agree with you. I'm not firing someone for using SHA1+nonce. But I will bitch if you recommend it, because even though it's not a game-over mistake, it's still a mistake.

Re: Ask HN: Which login method do you use?

#54

Post by lsc »

tptacek wrote: post #52
lsc wrote: post #49

Earlier quoted context omitted.

if passwords are randomly generated, I agree with you completely, and everything I've said is crazy talk. But most passwords are not randomly generated. Most passwords are dictionary words, or two dictionary words. You don't need to search the hash space; you only need to search the password space, and if everyone uses the name of their dog, well, that's not a very large space. http://www.schneier.com/blog/archives/2…

If passwords are two dictionary words, then even with the system dictionary, a single 50ms hash takes 889,251 hours to crack. 8 million if people put a single digit at the end of it. You won't win this argument.

adding two dictionary words and a number, yeah, that helps a lot. looks like you are right, and that if your users use 2 words and a number, and you use a hash that takes 50ms to calculate, you are probably OK.

but my point is that passwords are a lot less secure than they sound if you just add up the characters. And most hash functions take a whole lot less than 50ms of cpu time to calculate. Bcrypt does look pretty cool in it's ability to slow down brute force attacks. It does still require a minimum amount of entropy in the user passwords, though.

Re: Ask HN: Which login method do you use?

#55

Post by Confusion »

modoc wrote: post #4

I have my own code I use on my projects. It uses secure SHA 256 hashing for the passwords. The code handles registration, login, logout, and forgot password flows.

As opposed to insecure SHA 256 hashing?

Anyway, if you don't use a nonce per user or a time consuming hashing method, then all tptacek's comments apply. His link in http://news.ycombinator.com/item?id=576021 is worth your time.

Re: Ask HN: Which login method do you use?

#56

Post by siong1987 »

tptacek wrote: post #15
siong1987 wrote: post #14

Earlier quoted context omitted.

Rainbow Table is unavoidable. Block those IPs which have more than certain times of failed password. And, people usually cannot access to those hashed passwords.

Three sentences, three fallacies. (1) Not only are rainbow tables avoidable, but they've been trivially avoidable since Unix crypt(3) was invented in the '70s. The only way you can become susceptable to them is if you make the mistake of designing your own scheme. So don't do that. (2) There's a reason that no mainstream consumer application actually does this: as soon as you lock a normal user out of their account f…

Security is an never ending war. It is evolving. And, there is always a way to crack whatever you want(it may take time). But, the question is: do you really have to waste so much time on secure something? Or, you can use your time to implement something useful.

You are right. Use whatever auth system which is available.

Re: Ask HN: Which login method do you use?

#57

Post by weavejester »

tptacek wrote: post #37
weavejester wrote: post #34

Earlier quoted context omitted.

You're correct that rainbow tables are trivially avoidable, but it shouldn't take a single stupid mistake to expose your database. Password hashing is a last line of defense, not something that should ever be necessary unless something has gone very wrong indeed.

It shouldn't take a single stupid mistake to turn a string copy into a passwordless remote software update mechanism. $3+Bn USD of "shouldn't", down the drain. Can we talk about the real world, now? The reason Microsoft is driving modern offensive computing researchers nuts isn't that they got rid of the "stupid errors"; it's that they figured out how to make the runtime mitigate those errors with ASLR, NX, safe exce…

Could you give an example of a stupid mistake that could expose the database? SQL injection attacks are pretty hard to accidentally put into any reasonably well-built system, so I'm curious if you know of any other mechanism through which you could entice a database dump out of a web application.

I guess you could go after the OS or the web server, but I was under the impression you were talking about stupid mistakes from the web developer, not the developers of the OS or web server.

Re: Ask HN: Which login method do you use?

#58

Post by kineticac »

Just put the TwitterAuth gem into my rails app, and am using OAuth with twitter now. This is a niche though, meaning unless you already have twitter, or actually like it, it's a long process and could keep people from signing up. Logging in is easy though.

http://kineticac.posterous.com/rails-and-twitter-signin

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