Why to try get key out of white box crypto? How can one protect WBC itself? Help me understand the following. With WBC the question is mainly being stated as can one try to break WBC to identify the key. My question is: Why would one ever want to do that anyways?

If one can locate the WBC itself it should be enough to enc/dec anything she wants with the embedded key. To me it comes to chicken and egg problem where now one would need to "hide" WBC itself within the code to make it any practical.
This is an excellent question.  Unfortunately, I'm afraid I don't know of any really convincing answer.

In principle, one possible application of white-box cryptography would be to build a public-key cipher out of a symmetric-key cipher.  If you could build a white-box cryptographic implementation of AES encryption (say) where no one can recover the key nor figure out how to perform the decryption process, you'd have a public-key cipher.

However in practice I don't think that's actually the motivation for most work on white-box cryptography.  For instance, most published white-box crypto schemes can be easily inverted: given a white-box implementation of encryption, you can easily derive a white-box implementation of decryption.  Most published schemes focus on preventing you from recovering the key, instead of preventing you from figuring out how to perform the decryption process.  So, building a public-key cipher does not appear to be their motivation.

I don't know any really good answer to your question.  I know of two not-very-good answers:


One possible answer is that the code of the white-box cipher might be a lot larger than the key, and if a cracker wants to share it with others, they'll have to spend a lot more bandwidth sharing it than they would sharing the key.  However, this seems very weak and unconvincing.
Another possible answer is that white-box encodings are usually randomized: you can give a million people a randomized white-box implementation of AES decryption under key $K$ (the same key for everyone, but they each get a separately randomized white-box implementation).  Thus, if someone shares the code of their white-box decryptor, it uniquely identifies them.  However, in practice, this doesn't seem like a very effective defense against copyright infringement (prosecution is usually too expensive, and false identity too easy to forge).


So, I'm afraid I don't know of a strong practical motivation for white-box crypto.  Maybe someone else will have a better answer for you.