Imagine you wrote a decoder program with the key embedded in it. From looking at the program you can't work out what the key is, but you can use it to decode a

Imagine you wrote a decoder program with the key embedded in it. From looking at the program you can't work out what the key is, but you can use it to decode a secret message. You can have a secret encoder program too. Effectively blackbox obfuscation among other things allows you to turn symmetric encryption into asymmetric encryption. Another possible use is in cloud computing. You could prepare a program with private information in it and still safely submit it to a third party to execute. This would also be very useful with smartcontracts. Since the smart contract code is public it can't contain any secrets unless it's safely obfuscated. As I understand it we are still quite a way off from any of these techniques being feasible, since the overhead at the moment is huge.