31 Jan 2017

MTN TV scores, PowerVu developer apparently out of retirement?

Submitted by drhans

Well well, almost exactly 2 years after PowerVu being cracked wide open, it seems like Cisco (or whoever is now in charge of the thing you'd call "the most secure encryption" just 2 years ago) found an old PowerVu developer from the 90's, probably in some rural retirement home, with the task of saving the (pay-tv) world. Although he wasn't dead, he almost died of laughter when he learnt PowerVu was still in use.

Now you might ask what the hell made Cisco do this. As usual, the problem was most likely Premier League and the Sports 24 channel broadcast by the maritime pay-tv provider MTN. Otherwise it would be hard to imagine that MTN would be the first one to take the PowerVu situation seriously, if there wouldn't be the risk of losing Premier League rights since the pirate reception of MTN's Sports 24 channel was quite popular - just google it and you'll even see companies selling pirate boxes, almost looking like legitimate Sports 24 subscription.

So here you have the motivation. The first step for MTN was getting rid of EMM patterns and switching S-box from 00 to 0A. That didn't solve anything. Last year, MTN initiated 15-minute key change cycles. Of course, that didn't help either as there was nothing preventing people from finding as many EMM keys from old EMM logs as they wish. Now I was thinking that MTN would continue like this for another year or so - but that wasn't the case. Not so long after implementing the constant key rolling, MTN got another upgrade, immediately making all emulators obsolete.

So what happened? Well, hard to tell, these measures have been introduced just yesterday but the impact of that is that all EMM keys are no longer able to decrypt the EMM messages. There's another step that needs to be taken before the EMM message would now reveal an ECM key. From this point, I can just speculate what that step could be. My theory would be that Cisco boxes got a firmware upgrade which is now able to handle additional EMM decryption before sending it to the ISE for final decryption.

Nothing indicates that much else has changed, for example, I think that:

1) ISE is still in use, there haven't been any smartcards issued, which is still an option of course so even if the new way of getting EMMs to decrypt is found from the new firmware, it's not yet over for 0E 00

2) It also seems like sbox 0A is still in use

3) DES encryption didn't change either

4) Nor did the ECM and EMM message structure

5) I don't think the EMM keys had changed either

Some of these assumptions are based on the fact that, interestingly, the first byte of the encrypted EMM still decrypts just fine to 0x0C. Just the rest of an EMM is messed up.

In the end, this doesn't really seem like a big countermeasure or even something we could call "PowerVu2" but that doesn't mean it won't be effective. What this brings now is uncertainity. It shows the PowerVu system isn't dead yet and the steps taken by MTN suggest more providers will follow, upgrading their Cisco receivers. Remember, there's no real need to upgrade the old Scientific Atlanta boxes as all operators are phasing out SD distribution anyway.