I'm coming slightly late to this thread, but wanted to add a note... > If we did implement this approach, the next question is, could we also > implement a scheme whereby if the algo is changed, when someone goes to > change their password, the system can confirm that the old password is > provided correctly and then store the new password under the new scheme? >
If you do decide to use the passlib <http://packages.python.org/passlib>library (per João Gulineli's post <http://../d/msg/web2py/WEiNGgDya58/zoKCedgl-qwJ>), it also offers a CryptContext<http://packages.python.org/passlib/lib/passlib.context-usage.html#basic-usage>class which can configurably let you support multiple hashes at once; but more importantly (with regards the quoted question), it also lets you mark certain hash schemes as "deprecated", and offers a method verify_and_update()<http://packages.python.org/passlib/lib/passlib.context-interface.html#passlib.context.CryptContext.verify_and_update>method which takes care of that exact operation you described: verify password, and re-encode if previously stored using a deprecated hash (the function docs link to a usage example). - Eli Collins
