> If you care about the security of your account use a 20+ character random password and do not reuse that password at any other sites. There are several excellent password managers that can generate and remember such a password for you and make it easy to use. Here's a list: <link to list of password managers>.
> We allow all normal US printable characters in your password: upper and lower case A-Z, digits, and <list of punctuation>. Set your password generator to length 20+ and to use mixed case, digits, and symbols and you will be fine.
> If you think you might have to manually type this password at some point, you can use a reduced character set with a longer password. If you use just mixed case letters and digits make the password 22+ characters long. If you use just mixed case letters make it 23+ characters. Letters all of the same case? Make it 28+ characters. 32+ characters of hex is fine, too. Heck, you can make it all digits if you use at least 39 of them.
> If your password manager offers other options, such as patterns like groups of digits or pronounceable syllables separated by some symbol, that too is fine as long as you make it long enough. Make it long enough that your password manager gives it its highest strength rating.
> The exact upper limit on password length that our password entry fields allow might vary from time to time as we update the site, but will always be at least 64 characters.
NIST says there's no reason to limit password length any more[0]:
"Memorized secrets SHALL be at least 8 characters in length if chosen by the subscriber. Memorized secrets chosen randomly by the CSP or verifier SHALL be at least 6 characters in length and MAY be entirely numeric. If the CSP or verifier disallows a chosen memorized secret based on its appearance on a blacklist of compromised values, the subscriber SHALL be required to choose a different memorized secret. No other complexity requirements for memorized secrets SHOULD be imposed. A rationale for this is presented in Appendix A Strength of Memorized Secrets."
Is that why websites sometimes have low maximum password length requirements ? Ex: must be less than 20 characters.
Websites (like some banks used to) that have less-than 20 char limits for passwords are purely bad security strategy.
I've run across that at least once and it was a total pain to troubleshoot and figure out.
There needs to be a limit, yes, but surely something like 100 characters, or even 50, would be more sensible.
Banks all have systems that will stop you from attempting to bruteforce them.
"A password one megabyte in size, for example, will require roughly one minute of computation to check when using the PBKDF2 hasher."
I expect the parent's concern came from experience with PBKDF2, where the length is unbounded. It's good to consider possible denial of service attacks: if someone submits an enormous 1 MB password a PBKDF2 hasher can be knocked offline for 60s. Sha256 will quickly crunch that attack to a more manageable length.
https://en.m.wikipedia.org/wiki/Bcrypt
This sounds undesirable to me, so I'd support sha256 and an alternative.
I'd also recommend adding a max password length to any API. No point in allowing million character passwords.