Manual:$wgPasswordDefault

Details
Default password type to use when hashing user passwords.

Changing the default

 * 1) Check the "DefaultSettings.php" file in the   directory for the available and preset password encryption types. (As of MW 1.30: ,  ,  ,  ,   and  )
 * 2) Add   with the parameter to the "LocalSettings.php" file in case you want to change the encryption, e.g. to restore the old MD5 hashing:
 * 3) In order for the password to be saved in a new format, one login from each user has to be done.  This way the database is updated.  Alternatively you can use the  maintenance script to convert the hashing algorithm of all passwords without waiting for users to log in. Note that this script only works for ,.
 * 4) Check the MySQL-database whether the new format has been applied to the fields.