difference between video Scrambling and video Encryption

Question

I am bit confused between video scrambling and video encryption. I know both are the ways to make the safe delivery of the content and both have de-scrambler and de-crypt and use a key as well but in DVB broadcast we use scrambling at CAS level and not encryption like in MPEG2TS we send ECM info for scrambling.

So, my query is what is the exact difference between them, when to use what and why?

I know its a very common question but the googling is not giving much answers.

Can anyone help?

Answer 1

In case of Broadcast tv.

Scrambling is generating a 48-bit secret key called control word for the data stream .

And Encryption is used to protect the control word during transmission to the receiver: the control word is encrypted as an entitlement control message (ECM).

so first data is scrambled using control word and then it is protected using encryption by generating ecms

Answer 2

encryption is basically converting the signal into unreadable format. Secret keys like emm & ecm are encrypted .scrambling is process of restricting the access of Audio/Video content