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> When using bcrypt, make sure to use the following algorithm to prevent the leading NULL byte problem. and the 72-character password limit:

> bcrypt(base64(sha-512(password)))

Pre-hashing the password, in this context, without a salt, is susceptible to hash shucking: https://security.stackexchange.com/questions/234794/is-bcryp...

Instead, use:

  bcrypt(base64(sha-512(password + global_salt)))


The stack exchange article seems to ascribe the risk to using MD5. While adding a (global or appended data) hash as you suggest cannot hurt, I wonder if the suggested weakness exist for sha-512.


The same principle applies to SHA-512 just the same (much cheaper to attack non-stretched SHA-512 hash than attacking directly the bcrypt hash).

There are both MD5 hashes and SHA-512 hashes lying around, which makes "hash shucking" possible for both of them.


Firefox is great on desktop, been my primary browser for 15+ years.

Sadly though, the mobile version (still) lacks support for "pull to refresh" gesture. Other than that, mobile FF is great (privacy features, browser addons...).


This was probably the most notorious misuse of scrypt.

Memory usage of scrypt was tuned to take 128KB, which made Litecoin mining ~10 times faster on GPUs than on CPUs.


Some of this is good advice, but there's a BIG point on the 'Password Storage Cheatsheet' that's linked and referenced by the above article, that I don't think is solid.

I read they recommend to use the both (adaptive hashing and "local parameterization"). As even if you utilize separate device (HSM for example) for encrypting the passwords (I'd encrypt instead HMAC), you should indeed not give up on adaptive hashing.

Here's some good commentary on this by Solar Designer (user solardiz on Reddit): http://www.reddit.com/r/netsec/comments/26d52c/yescrypt_pass...


"I read they recommend to use the both (adaptive hashing and "local parameterization")."

I read their text as recommending A or B, based on the intro where they state "Two approaches facilitate this, each imperfectly."

"As even if you utilize separate device (HSM for example) for encrypting the passwords (I'd encrypt instead HMAC), you should indeed not give up on adaptive hashing."

Right, this is the sort of thing that led me to hedge by saying I MIGHT be convinced if an HMAC were involved; it still gives me pause, for sure.


Before the Breaker 101 course starts, I invite you to take a quick (15 questions) quiz about web application security practices and quirks: http://timoh6.github.io/WebAppSecQuiz/index.html


> But salts don't have to be strictly unique, they only have to be a barrier to rainbow tables.

Rainbow tables are not the only "attack vector" that proper use of salts defeats.


What else do they protect against?


At least, testing passwords against multiple hashes (at the price of one) is impossible. And it is not possible to see if different entries shares a same password (or to see if they have a different password). Also, it (probably unintentionally) mitigates timing attacks when comparing if the entered password matches.


>testing passwords against multiple hashes (at the price of one) is impossible

That's defending against a newly generated rainbow table.

> And it is not possible to see if different entries shares a same password (or to see if they have a different password).

That's repeating the first point with different words! It's defending against a pre-generated table. i.e. a rainbow table.

Timing attacks are not mitigated by salts; they're mitigated by the design of the encryption. You should not rely on salts for this. In fact, if your hash is exposed you should assume your salt is also exposed.

What do salts guard against other than rainbow tables?


> That's defending against a newly generated rainbow table.

You lost me here. Anyway, the attacker does not need a rainbow table at all to attack against multiple hashes at the price of one.

> That's repeating the first point with different words! It's defending against a pre-generated table. i.e. a rainbow table.

Again, no rainbow tables at all are needed to see if different entries shares a password or not.

About timing attacks, see my earlier comment in this comment chain.

> You should not rely on salts for this. In fact, if your hash is exposed you should assume your salt is also exposed.

I see and agree with your point about "relying on salts", but salts just happens to (as a side-effect probably) mitigate the attack. Remember, your salts are not exposed "as-is" if the attacker manages to fetch the password hash using timing.


As long as the salts are relatively unique, the first two aren't an issue. I don't understand how salts could help against timing attacks, though.


> I don't understand how salts could help against timing attacks, though.

The salt which is unknown/unpredictable (and contains enough entropy) to the attacker makes his offline attack against the hash unfeasible (after he has managed to fetch the password hash from the server using timing leaks). I'm not sure if it is possible to fetch the (whole) hash using timing, because it is not a direct comparison. But anyway, if the attacker managed to do that, now because of "a proper salt" he would have to crack a hash that was composed of, say, 128 bits of salt and 20 bits of the actual password. It is unfeasible because of that 128 bits of salt alone.


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