Read the bcrypt paper: http://www.usenix.org/events/usenix99/provos/provos_html/index.html http://www.usenix.org/events/usenix99/provos/provos_html/ind... The

Read the bcrypt paper: http://www.usenix.org/events/usenix99/provos/provos_html/index.html http://www.usenix.org/events/usenix99/provos/provos_html/ind... The algorithm requires (cost, salt, password) as input, and the output hash includes the cost and salt. When generating a hash for a new password you should of course be choosing this salt randomly, and when checking a password be using the stored cost and salt. In particular see the Implementation section: An important requirement of any bcrypt implementation is that it exploit the full 128-bit salt space. OpenBSD generates the 128-bit bcrypt salt from an arcfour key stream, seeded with random data the kernel collects from device timings.