I am working on upgrading my code base to PHP-7 and I'm having trouble with some old users that have a salt format that is not compatible with DES. My idea is to authenticate the user and then transform the hash salt into a new format like Blowfish that is compatible with the new crypt.
The problem comes when I try to use 'crypt()' with the old salt in order to authenticate the user before changing the salt, I get the following error:
crypt(): Supplied salt is not valid for DES. Possible bug in provided salt format.
Is there are way to use crypt (or an alternative function) with other algorithms so I can use the old format salt?
For the people that have the same problem, I solved it using password_verify that actually underneath uses password_hashwhich supports existing password hashes as Joachim suggested.