How? If you can truncate user passwords, you should never handle user passwords again, unless you’re a student or hobbyist learning a valuable lesson.

Yeah. The real reason to be alarmed is worse than the obvious one.

If a partial version of what was originally set actually works later, it implies a scary chance they're not even hashing the password before storing it.

[–] kautau 5 points 1 week ago

I think it's a nonzero chance they're not hashing it. Pretty much every hashing function, in the interest of preventing collisions, provides vastly different responses on small amounts of input. Even if they were hashing it, it would just appear to be the same password in a situation where they somehow got a collision, but again, the column length for passwords would always be fixed since a hash function always outputs the same data length.

[–] [email protected] 1 points 1 week ago* (last edited 1 week ago) (1 children)

Also suggests the user may be reusing the same prefix if only the changed bits are getting truncated.

Should use different random passwords every time. Completely random or a random string of words. While it doesn't solve the cleartext password storage issue, a data breach won't compromise all your other accounts to same degree.

Doesn't hurt to also randomize usernames, emails, and even security question answers.

edit: or my new favorite passkeys, just make sure you trust whatever tool is managing your private keys.

[–] kautau 5 points 1 week ago* (last edited 1 week ago) (1 children)

Not how password hashing works. Demonstrated with sha256:

hunter2butitsreallylong:
a9953dfbfec699349341edc857dcfe5c7a617c81f312cf57297d5b852881bab3

hunter2:
f52fbd32b2b3b86ff88ef6c490628285f482af15ddcb29541f94bcf526a3f6c7

a hash algorithm encompasses all provided data and returns a single fixed length data response

https://en.wikipedia.org/wiki/Cryptographic_hash_function

Any changes, even just removing a few characters, drastically changes the output of the hash function (https://en.wikipedia.org/wiki/Avalanche_effect)

You have no way of knowing a user password when you are storing hashes, you can't truncate them, and the user password length doesn't matter (up to a certain point where it's technologically dumb to hash user input over a certain amount of data)

I do agree however that changing / randomizing your password is important, as someone brute forcing or running rainbow tables etc on a hash dump can quickly attack a common password across different dumps

[–] [email protected] 2 points 1 week ago (1 children)

Ultimately we don't know the implementation. I've seen some bad sites like stealth truncating on the registration form but leaving the login form unbounded so the password you pasted in both times doesn't work.

Separate issue from truncating, I get suspicious when I see passwords capped to 16-20 chars for the reason you gave that they should be stored as fixed length hashes.

[–] kautau 1 points 6 days ago

That’s true, there’s no way to know what sort of back asswards string modifications are happening to the password before it makes it to a hashing function, if it ever does. But the OP did say they told him his previous password was too long, and he was required to change it, so they were either storing it in plaintext, or storing the length of it somewhere. One is really really bad, one is weird, but also bad