In general, using the defaults (mcrypt_create_iv() using dev/urandom for the salt and bcrypt with a work factor of 10 are specified with PASSWORD_DEFAULT in the

In general, using the defaults (mcrypt_create_iv() using dev/urandom for the salt and bcrypt with a work factor of 10 are specified with PASSWORD_DEFAULT in the curreent implementation) along with password_needs_rehash() will keep you up to date with no "retouch" necessary. When the default changes, password_needs_rehash() returns true, and you then rehash with the new defaults. All you need to do is make the db column wider than necessary for the current defaults to put maintenance off into the future. (The only real problem is that the hash function truncates passwords at 72 characters at the moment, which will force you to pre-hash the user value with something like SHA256 for very long passphrases.)