How do encryption services work

[stoneyja]

Hi everyone, just wondering how does NDS videoguard work and how is it different to N3 and what is a patched reciever

[TheCoder]

Originally Posted by stoneyja

Hi everyone, just wondering how does NDS videoguard work and how is it different to N3 and what is a patched reciever

In essence there is essentially no difference between the two (or indeed, any other TV encryption system).

The 'System' (NDS/Nagra/Conax etc) doesn't actually encrypt the video/audio. It only encrypts something called the CW's (codewords). These CW's are the things used to actually descramble the mpeg video/audio information via a DVB standard algorithm called the DVB-CSA (Common scrambling algorithm). All DVB platforms use this same algorithm to actually descramble the video/audio.

Most smartcards consist of handlers for two seperate datastreams called ECM's (Entitlement control messages) & EMM's (Entitlement management messages). The ECM's are messages which contain the encrypted CW's and the response is a decrypted CW (it may be re-encrypted using a different method that a particular box understands - hence pairing). EMM's are messages which control how the card deals with ECM's, for example, setting up access to certain channels or tiers only. When you add another channel to a card the providers subscriber control centre will send out a specific EMM that only your card understands that will configure the card to accept ECM's for the new channel.

Pretty much all TV smartcards work in the above described manner. Where they differ is simply in the implementation of the methods. They may use different encryption algorithms and probably a different protocol (its like them speaking a different language).

A 'patched' receiver can mean many things. Generally it simply means that the box has been modified to do something that its original firmware was not intended to do. It can often mean adding code to implement a 'SoftCam' or similar (a 'SoftCam' is basically something that pretends to be a smartcard in that it generates decrypted CW's).