Jesse's change to add the -secret option.

This mechanism enables the installed JNLP slaves to retrieve the *.jnlp file from the server without using a valid user credential.
Java 1.6 dependency
Use a proper block cipher mode.

If we let each 16 byte block encrypted separately (as in the default ECB
mode), it still reveals too much without even knowing the secret key.
fixup
got these two parameters mixed up
Jenkins