# Tag Info

1

When using a salted, key-stretching KDF, like PBKDF2 or scrypt, you are in effect stretching both the salt and the password. That is to say, what you're calculating is $$\rm key = KDF(password, salt)$$ where changing either of $\rm password$ or $\rm salt$ requires the slow $\rm KDF$ function to be entirely recomputed. In fact, if changing the salt did ...

0

To answer your literal question: "Specifically, is it practically possible to increase the difficulty of someone with knowledge of $\rm pass1$ to derive $\rm pass2$ to be more than the difficulty of guessing $\rm password$ itself, even if it requires spending portions of available $\rm password$ entropy?" The answer is "no". To see why, observe that, ...

5

Having a random length makes very little total difference in the entropy of your password compared to the entropy you would get using just the maximum length allowed. This is because there are a lot more passwords of, say, length 10 than any shorter length (in fact, there are more 10-character passwords than any other shorter password). So if your attacker ...

1

Some devices I've been working with do indeed update biometric information. The reasons is that there may be additional information: acceptable fingerprint was scanned (required features are found), but the scan shows some area of finger not involved in previous scans. some other additional information helping make more exact scans in the future

0

The first thing I would want to know is if the encoding is deterministic. This should be easy to test. Change the password, but make it the same value. If the value in the DB doesn't change, then it is deterministic. Also try this for a few users. Give them all the same password and see if the DB entries are the same. If so, you don't really even need to ...

0

One potential consideration is that combinations of security principles may have unintended vulnerabilities. This is not to say they you cannot combine such approaches, but most combinations have been well studied and then recommended by trusted 3rd parties (academic or governmental or institutional). While not in the same domain has hash functions, the ...

2

One potential issue with this strategy revolves around compliance. You might be subject to various regulations (such as Government/DoD regulations) that prohibit unsafe hash functions. You might have a very unpleasant experience trying to explain to the audit team how using MD5 as part of user authentication does not mean "the terrorists win!"... In the best ...

5

As K.G. and nightcracker note, the reason we don't recommend this method of password storage is that it becomes insecure if the secret $k$ is compromised. Given that the whole point of password hashing is to protect the passwords in the event that your server is compromised, it's generally not safe to assume that the compromise won't include the secret key ...

4

You can, but you don't because you need secure storage for $k$ as well as a secure computing platform. Those things are expensive.

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