Re: [RFC] Throw error for passwords longer than 72 bytes in password_hash() with bcrypt

On Tue, Sep 29, 2026, at 14:04, Kamil Tekiela wrote: > On Tue, 29 Sept 2026 at 12:35, Sjoerd Langkemper wrote: > > The proposal is to throw a ValueError when a password longer than 72 characters is passed > > to password_hash and bcrypt is used. > > Checking that the input is less than 72 bytes long is the > application's responsibility, not the algorithm's. Thank you for your feedback. It is clear to me that you oppose my proposal as is. Do you have a suggestion for improvement? Something I can change that would restrict misuse of password_hash but would have your approvement? > there will be users that will try such passwords and the > application will crash for them instead of working correctly as > before. Yes, this can happen. This is an intentional tradeoff: my proposed change makes the situation more secure, but could crash applications in some situations. I described in the RFC that users rarely/never use passwords longer than 72 characters, so I think this is acceptable. > Such a limitation would only help in really egregious cases of misuse, > when a developer prepends an almost 72-byte string to a password or > passes something other than a password as input. Both should be caught > in a code review by a senior developer, not runtime. The FreshRSS case is interesting here. Each change was reviewed and seemed secure, but the combination resulted in authentication bypass. https://pentesterlab.com/blog/freshrss-bcrypt-truncation-auth-bypass Regards, Sjoerd