BCrypt
BCrypt Pbkdf implementation.
This was originally based on https://github.com/hierynomus/sshj/blob/master/src/main/java/com/hierynomus/sshj/userauth/keyprovider/bcrypt/BCrypt.java .
public BCrypt()
Applies the Bcrypt kdf to derive a key and iv from the passphrase,
the key/iv are returned in the output variable.
Ported from the SSHJ library. https://github.com/hierynomus/sshj