http://giggles.vernccvbvyi5qhfzyqengccj7lkove6bjot2xhh5kajhwvidqafczrad.onion/tutorial/encrypt-pendrive.html
If all ok, just proceed to the following step.
[ Step 3 - Opening your device ]
This is the way you will make your pendrive ready to be used, you need to "open" it, which will acctually map it to another file where you will can use it and will have encryption going on in a tranparent manner: sh-5.1 # cryptsetup open /dev/sdb pendrive...