Because the format of hashed string ($2y$10$salt....) itself gives clues to hacker(i.e, who hacked the DB) that the encryption is done using Bcrypt algorithm and so he can easily hack by using password_verify() in php by passing parameters as his guess passwords.
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3I wouldn't say 'easily': brute forcing Bcrypt will take a very, very long time.Jim– Jim2014-06-23 13:42:43 +00:00Commented Jun 23, 2014 at 13:42
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Yes, it is fine to do so. Brute force attacks on bcrypt are not a very effective method, especially when you increase the cost.Brett Santore– Brett Santore2014-06-23 13:45:42 +00:00Commented Jun 23, 2014 at 13:45
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1 Answer
There is no disadvantage in storing those BCrypt hashes directly in the database, none of the parameters are meant to be secret. Furthermore they allow to switch to a better algorithm (or increase the cost factor), without becoming incompatible with older hashes.
If those parameters would be hidden somehow, an attacker would have to guess them. But there are not this many possible values, a cost factor e.g. only makes sense between 9-13. If you really want to add such a server side secret, there are much better ways to do it. You could encrypt (two-way) the already hashed values with a strong key, then an attacker has to "guess" this key, which is impossible.
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user3767551
Some where in the internet i saw, bcrypt is based on Blowfish cipher. But it seems Blowfish implementation is having both encrypt and decrypt also. so it means is it possible to decrypt the bcrypted hash values ?
martinstoeckli
@user3767551 - It is true that BCrypt is based on Blowfish, but while Blowfish is an encryption algorithm (two-way), BCrypt is a true hash algorithm (one-way).