> If they describe how passwords were hashed, it would make it easier for hackers to crack them.

I don't really agree with you.

If you store bcrypted stuff, you see $2a${integer exponent}$hash.

If you store SHA1'ed stuff, you see characteristic hashes and can trivially test against known hashes. So on for MD5, etc.

I don't need you to tell me "we store SHA1'ed stuff iterated 35 times with the following salt", but keeping that information secret wouldn't usually help you anyway. A determined attacker will test and iterate until they've figured out your scheme (or, if you're unlucky, they won't need to).

Telling the attacker "we bcrypted everything" doesn't tell them anything they couldn't plainly see on their own.

You may be joking, but for the sake of other people who might read that and not know the reality of the situation:

That is not the case. Even just the length makes it pretty clear which hash is in use ( https://en.wikipedia.org/wiki/List_of_hash_functions ), and even assuming some crazy "security" scheme in use for storing them (hashing and then padding, or some such), someone with the hashes only has to figure out one password to figure out the procedure used. Given the high likelihood of there being "password" or "12345" hashed somewhere in there, that's not so hard.

You are correct; any wise attacker would create accounts with known properties before compromising the database for these purposes.

No it doesn't. Attackers can obviously be presumed to have some number of password,digest pairs; for instance, for their own accounts. From that information it should be trivial to figure out the scheme used.

This of course leaves aside the fact that, having compromised any significant portion of the app, they are probably ε from source code anyways.

Kerckhoff's principle: "A cryptosystem should be secure even if everything about the system, except the key, is public knowledge."

This applies here too. If it's secure, which good hashing is, releasing the details should have little to no effect on the security of those hashed passwords. It's also trivial to determine what the hashing scheme is in many cases.

It seems like there are a number of trivial ways to determine what method was used to hash the passwords. For example, hash a common password like `password` or `password123` with all common hashing schemes and compare see which of the resulting hashes are in the list of hashes you got from kickstarter.

That's not how a properly implemented hash -- and cryptography in general -- is supposed to work.

This strategy is called "security by obscurity", and is seen as a very bad one.

Instead, cryptography aims to provide means to encrypt data in a way that anyone knows //how// it was encrypted, and still doesn't have a clue how to decrypt it -- because they don't have the key, in case of encryption, and because the hash is a "one-way" function, in case of hashing.

Disagree for systems. I take adding "security through obscurity" to the normal standard good methods as a defense in depth measure.

Adding "security through obscurity" is only a net win over "published security scheme" if your engineers are substantially better than any engineers who might comment on your published scheme. Even if you've hired world-class security engineers, there could still be some flaw they've overlooked, that an outside commentator might notice.

Note that the security of a whole system is harder to get right than the security of any one component; keeping it obscure just makes it much less likely that a white hat will notice the flaw and notify you. A simple example of this is the freshman CS majors' perennial idea that combining multiple PRNGs will yield a "more random" algorithm (it typically makes the result easier to predict). There are plenty of cases of a secure algorithm being used to build a system that ends up insecure because of some obscure flaw that nobody noticed initially.

"Adding "security through obscurity" is only a net win over "published security scheme" if your engineers are substantially better than any engineers who might comment on your published scheme."

I think that overstates the case. Your engineers don't have to be better, just good enough know what's correct and safe, or do research until they know.

My approach is to just add things that are clearly correct to published and studied systems that are thought to be correct. In this case, we're talking about applying multiple or multiple runs of one way hashing functions; I'd actually do some research before trying the latter, but it strikes me as safe, and the former is by definition safe, right? Whereas it would never even occur to me to combine PRNGs ... or not use a hardware source of entropy to begin with in the first place (they aren't that expensive in the scheme of things).

and that is exactly how we get clowns like linkedin storing all of their passwords as unsalted hashes...

See my other comment on starting with "published and studied systems that are thought to be correct". Salting your passwords has been state of the art for so long I can't remember when I first heard of it.

LinkedIn was not adding any sort of reasonable defense in depth security through obscurity, but foundational gross negligence.

Shouldn't matter. Something like "We hashed each password using PBKDF2 and a unique salt and a high number of iterations" doesn't help all that much. The attackers will still have a tough time brute forcing those.