Paper - 1999 USENIX Annual Technical Conference, June 6-11, 1999, Monterey, California, USA
A Future-Adaptable Password Scheme
Niels Provos and David Mazières
Many authentication schemes depend on secret passwords. Unfortunately, the length and randomness of user-chosen passwords remain fixed over time. In contrast, hardware improvements constantly give attackers increasing computational power. As a result, password schemes such as the traditional UNIX user-authentication system are failing with time.
This paper discusses ways of building systems in which password security keeps up with hardware speeds. We formalize the properties desirable in a good password system, and show that the computational cost of any secure password scheme must increase as hardware improves. We present two algorithms with adaptable cost--eksblowfish, a block cipher with a purposefully expensive key schedule, and bcrypt, a related hash function. Failing a major breakthrough in complexity theory, these algorithms should allow password-based systems to adapt to hardware improvements and remain secure well into the future.
Niels Provos and David Mazieres
This paper was originally published in the
Proceedings of the 1999 USENIX Annual Technical Conference, June 6-11, 1999, Monterey, California, USA
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