BCrypt of PHP cannot verify the password

Question

I have tested the password_verify of PHP that does not verify correctly. I am using centOS and PHP version 5.3.3. I know the 5.3.3 version of PHP does not provide the password_hash function, so i have used the https://github.com/ircmaxell/password_compat

However, it is always to return true with different passwords when i verify it. Is my code has bug?

Here is my code:

    $password = 'k32AlGOPqvCzoh*Sp(Hdrr26]M=lQb00R&W=hew|-|([(03vp==A8%m?l=eA2^bs_|\qVV3WZ';

    $verify_pw = 'k32AlGOPqvCzoh*Sp(Hdrr26]M=lQb00R&W=hew|-|([(03vp==A8%m?l=eA2^bs_|\qVV3WZasdasdasdasdqweqa13123';

    $options = array(
                'cost' => 15
            );

    $hash = password_hash($password, PASSWORD_BCRYPT,$options);

    var_dump(password_verify($verify_pw ,$hash)); // always true

I don't think you'll find much random in password_verify() but if you really believe that there is a bug in the code then you create a SSCCE to prove your assertion and post an issue on github for the compatibility pack, or a bug report on bugs.php.net — Mark Baker
– Mark Baker, Commented Nov 25, 2015 at 8:08
But it is really happen to me, that is very sad what i get. I know password_verify() should be work correctly, but still cannot figure it out what thing cause this happen at my level. Or i should provide more info. — Jacky Shek
– Jacky Shek, Commented Nov 25, 2015 at 8:30
bcrypt by design always give out different hash output, look at this sof question. or just try this bcrypt calculator. However, i wonder if your different password means different plain text or a same plain text that passed into bcrypt and spit out different output - please verify. also, notice several first characters in your hashes, it defines hash length and salts, wiki had explained this. — Bagus Tesa
– Bagus Tesa, Commented Nov 25, 2015 at 8:41
well, it stated in wiki that Many implementations of bcrypt truncate the password to the first 72 bytes.. tried to shorten your password, it works as expected. — Bagus Tesa
– Bagus Tesa, Commented Nov 25, 2015 at 8:57

ins0 · Accepted Answer · 2015-11-25 08:51:40Z

2

The problem is not your code. Bcrypt has a string limit from 56 bytes e.g. 55 Chars

https://www.usenix.org/legacy/events/usenix99/provos/provos_html/node4.html

the key argument is a secret encryption key, which can be a user-chosen password of up to 56 bytes (including a terminating zero byte when the key is an ASCII string).

So your string gets truncated and is the reason why your password_verify returns allways true as the truncated strings are identical.

answered Nov 25, 2015 at 8:51

ins0

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3 Comments

Jacky Shek Over a year ago

Thank you very much, therefore i need limit user characters length or use SHA-512 with sperating random salt. Am i right?

ins0 Over a year ago

Internally the algorithm manages characters better so you can go to at least 71 characters in total. I don't know if SHA-512 has a similar behavior

Bagus Tesa Over a year ago

SHA-512 should do it, it'll make digest of the string.

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