This will NOT replace a lost or broken key that shipped with any of the Cubase family of products. It is for use with VST instruments that did not include the key originally in the package. You must contact Steinberg directly for help with a lost or broken key for any Cubase products which originally came with the key, this will not help you with that situation.
The USB-eLicenser (formerly "Steinberg Key") is a copy protection unit (sometimes called "dongle") which is needed to use Steinberg's software range. With the host applications Cubase, Nuendo and WaveLab, the USB-eLicenser is already included in the product package. The USB-eLicenser is also required to run Steinberg VST instruments, but is not included in the product boxes and must be purchased separately if no USB-eLicenser/Steinberg Key is already present on the system.
The USB-eLicenser is actually a tiny computer which stores licenses for Steinberg products, and is connected to a USB port on your computer. All current Steinberg products that use a copy protection device use exactly the same system. The Steinberg copy protection system allows the storage of several licenses on the same USB-eLicenser. Licenses can also be transferred between USB-eLicensers with certain limitations. This can be very useful, for example in the unlikely event of a Steinberg customer wishing to sell a product.
*This applies only for the full version of the product, as updates do not contain a Steinberg Key (USB-eLicenser).