That being said, from a security standpoint, any gain in entropy by adding characters would be negligible past a certain point.
That would be completely based on the hash being used. In the example above I showed SHA512 which is 64Bytes. If we’re using ASCII (7 bit per character) as our input then 64 Bytes is just over 73(73.1428…) characters. After that you’re losing data in the hashing process and by that effect it would be negligible… (There’s some wiggle room here in that we can’t type hidden ASCII characters so some passwords over 73 characters would fill those spaces… but detecting collisions is silly and non-trivial… better to just not worry about those at all.)
Extended ASCII would be same premise, just 64 characters instead of 73.
The reality is that nobody is using much more than 64 Bytes for their hashing algorithm for passwords… 64 characters is a good number to max out most of them. Databases don’t need to store much at all regardless of the length of your actual password. If you’re developing an app you can set the database to limit based on the algorithms you’re using. If you have no idea what the web-dev will actually use… then 128 characters on the database field is probably pretty safe (88 I think if storing as Base64, 128 if storing in Hex. Could be off by one here.) and literally trivial to store. The point being that even if every one of your users submitted 10000 character long passwords… that’s irrelevant and trivial for storage as hashes.
There’s a more practical limit. Using US standard keyboard symbols, a 40 char password is about as secure as a 256-bit block cipher key. That’s impossible to break due to thermodynamic limits on computing.
The reason to put a high char limit is to mitigate DoS attacks. It can still be a few hundred chars.
That would be completely based on the hash being used. In the example above I showed SHA512 which is 64Bytes. If we’re using ASCII (7 bit per character) as our input then 64 Bytes is just over 73(73.1428…) characters. After that you’re losing data in the hashing process and by that effect it would be negligible… (There’s some wiggle room here in that we can’t type hidden ASCII characters so some passwords over 73 characters would fill those spaces… but detecting collisions is silly and non-trivial… better to just not worry about those at all.)
Extended ASCII would be same premise, just 64 characters instead of 73.
The reality is that nobody is using much more than 64 Bytes for their hashing algorithm for passwords… 64 characters is a good number to max out most of them. Databases don’t need to store much at all regardless of the length of your actual password. If you’re developing an app you can set the database to limit based on the algorithms you’re using. If you have no idea what the web-dev will actually use… then 128 characters on the database field is probably pretty safe (88 I think if storing as Base64, 128 if storing in Hex. Could be off by one here.) and literally trivial to store. The point being that even if every one of your users submitted 10000 character long passwords… that’s irrelevant and trivial for storage as hashes.
There’s a more practical limit. Using US standard keyboard symbols, a 40 char password is about as secure as a 256-bit block cipher key. That’s impossible to break due to thermodynamic limits on computing.
The reason to put a high char limit is to mitigate DoS attacks. It can still be a few hundred chars.