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Date: Sun, 9 Feb 2025 15:20:40 +0000
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Subject: Re: [PHP-DEV] bcrypt warning on long passwords
To: Rob Landers <rob@bottled.codes>
Cc: internals@lists.php.net
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From: tekiela246@gmail.com (Kamil Tekiela)

Hi,

I would say that this is a pretty bad idea. 72 bytes of entropy are
quite a lot for *PASSWORDS*. Even if some users use a pass phrase
longer than that, the first 72 bytes are enough to provide sufficient
security. People who use it for other stuff, like in the linked
article, are only to blame themselves. They use the wrong tool for the
job. The limitation of bcrypt is very clearly documented[1].

Triggering a warning at runtime wouldn't be useful to the developer.
To avoid such a warning they would need to either reject passwords
longer than 72 bytes or truncate them before passing it to
password_hash. Both approaches provide no additional security or any
other value. That would only annoy either the developers or the users.

Letting bcrypt use only the first 72 bytes is a very safe and easy
solution. No need to overcomplicate it.

Regards,
Kamil

[1]: https://www.php.net/manual/en/function.password-hash.php#refsect1-function.password-hash-parameters