Interesting idea! So for example, the user would provide the displayed hex digest as a note along with the payment. The payment verification server could then email the user the decrypted key.
Yeah, or more likely a Bitcoin address and payment amount would be generated based on the attacker's Bitcoin public key and a hash of the encrypted key. Then the victim would pay that address and somehow contact the attacker (email, forum, twitter, whatever). The point is that the attacker could rely on the victim's human ingenuity to make it harder for the authorities to block payments.
