Eksblowfish is a variant of the Blowfish cipher, modified to make the
key setup very expensive.  ("Eks" stands for "expensive key
schedule".)  This doesn't make it significantly cryptographically
stronger, but is intended to hinder brute-force attacks.  It also
makes it unsuitable for any application requiring key agility.  It was
designed by Niels Provos and David Mazieres for password hashing in
OpenBSD.

Eksblowfish is a parameterised (family-keyed) cipher.  It takes a cost
parameter that controls how expensive the key scheduling is.  It also
takes a family key, known as the "salt".  Cost and salt parameters
together define a cipher family.  Within each family, a key determines
an encryption function in the usual way.

This distribution also includes an implementation of "bcrypt", the
Unix crypt() password hashing algorithm based on Eksblowfish.