There is a huge terminolgoy confusion - the actual encryption algorithms are pretty much your usual classical ones only... it's only the "key distribution" mechanism that has a quantum aspect to it.
So, getting an "imperfect" copy of the key (and with a phase-covariant cloner as mentioned in the article, you can do that with a fidelity of ~0.83) means you've broken into the entry level already. Now, if the key was being utilized to encrypt say, an-already-encrypted-data, then it's down to your classical cryptographic schemes to break open that cipher
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There is a huge terminolgoy confusion - the actual encryption algorithms are pretty much your usual classical ones only... it's only the "key distribution" mechanism that has a quantum aspect to it. So, getting an "imperfect" copy of the key (and with a phase-covariant cloner as mentioned in the article, you can do that with a fidelity of ~0.83) means you've broken into the entry level already. Now, if the key was being utilized to encrypt say, an-already-encrypted-data, then it's down to your classical cryptographic schemes to break open that cipher