NetAuth stores secrets for entities. These secrets need to be cryptographically armored so that they can be stored with confidence. The cryptography engines of NetAuth are implemented on a plugin architecture, and can be chosen based on the needs of a particular site.
Swapping cryptography systems is not supported, so choose carefully. It is possible to build an engine that supports reencryption or re-hashing, but the provided engines do not do this.
The bcrypt engine is the only one compiled in by default. From Wikipedia:
bcrypt is a password hashing function designed by Niels Provos and David Mazières, based on the Blowfish cipher, and presented at USENIX in 1999. Besides incorporating a salt to protect against rainbow table attacks, bcrypt is an adaptive function: over time, the iteration count can be increased to make it slower, so it remains resistant to brute-force search attacks even with increasing computation power.
bcrypt is the default engine and unless you have a good reason why you should implement another cryptography engine, stick with the defaults.