In such a situation, the only recourse for attackers is to clone smartcards, i.e. Nowadays, the publishers have begun to learn, and they use proper encryption. Of course, such secrets were never maintained for long because reverse engineering works well and, inevitably, these homemade encryption algorithms almost invariably turned out to be pathetically weak and breakable. In older times, media publishers had the habit of doing everything "their way", which means that they designed their own encryption algorithms, and they were very proud of them, and kept them secret. The next time K is updated (it happens several times per day), the ex-subscriber is "kicked out". When a subscriber is no longer a subscriber (he ceased to pay), the publisher simply stops sending the blob containing K encrypted with the corresponding K s. Thus, a given decoder will just wait for the blob which contains K encrypted with his card-specific key K s, and use the card to obtain K and decrypt the stream. That is, every minute or so, thousands of small blobs are sent in some "holes" in the data stream (apparently there is sufficiently free bandwidth for that) all these blobs contain K, but encrypted with the key of a subscriber. Along with the media stream, the publisher sends K encrypted with each K s in circulation.The media stream is encrypted with a key K.Each subscriber has a smartcard, and that card contains a key K s specific to that subscriber.The generic problem is known as broadcast encryption. The receivers cannot do anything but receive they cannot emit anything.
A satellite TV system must face the following challenge: it is one-way.
0 kommentar(er)
