It's highly unlikely you'll be able to decrypt it, as you would also need to know the Base Derivation Key (BDK) and/or the Inital PIN Encrypting Key (IPEK) which the manufacturer has embeded into the device. You'd also need to know how they generate the KSN from the BDK. They're unlikely to share all that information with you, as it would render the encryption useless.
Source: http://en.wikipedia.org/wiki/Derived_unique_key_per_transaction
Which leads onto the next question. Why do you want to decrypt this information? The plain text portion of the returned data contains (PCI Compliant) segments of the card number (first four digits, last four digits). If you were able to decrypt the full card number, then the full weight of PCI compliance would fall on your shoulders, and consequently make using a 3rd party device useless.