4 ms·

Ah, I thought L1 keys were burned into hardware, so blacklisting this key was effectively blacklisting a bunch of Lenovo tablets from accessing 4K HDR streaming

Ah, I thought L1 keys were burned into hardware, so blacklisting this key was effectively blacklisting a bunch of Lenovo tablets from accessing 4K HDR streaming? Edit: looks like I'm wrong about this, and the Widevine L1 keys can be changed with a firmware update. There's an interesting breakdown of how it works on Qualcomm chips here: http://bits-please.blogspot.com/2016/04/exploring-qualcomms-secure-execution.html http://bits-please.blogspot.com/2016/04/exploring-qualcomms-...

londons_explore 5y ago
Does this mean if I have a lenovo tablet that currently streams 4K, that it will lose 4K video support? Could I ask Lenovo for a refund?
- nikanj 5y ago
  Yes and yes. Lenovo probably doesn’t give a shit, though. But you can ask!
  - Scoundreller 5y ago
    Depends on the country. Some do have some liability on manufacturers and/or vendors for defects. Unsure if an asterisk in their click through contract about key revocation would even matter.
- garblegarble 5y ago
  I would think so (the repo suggests this is a Lenovo TB-X505X key, I'd imagine they're at least per-product). I could certainly be be wrong about L1 keys being burned-in, that was just my understanding of it (vendor docs say things like "Hardware DRM", but maybe I'm jumping to conclusions from marketing speak) The Widevine spec doesn't say either, it just says that all processing is within the Trusted Execution Environment, so I suppose the keys could be loaded/updated in firmware. I'm looking for more docs now... Edit: looks like I was wrong and they can be changed with firmware updates: http://bits-please.blogspot.com/2016/04/exploring-qualcomms-secure-execution.html http://bits-please.blogspot.com/2016/04/exploring-qualcomms-...
  - alias_neo 5y ago
    TEE is an environment with hardware backed attestation, you run a piece of software in the "black box" to do things like key generation etc. My educated guess, having used TEE/TrustZone for keys is that they could update the payload (the "Trusted Executable") with a new one to resolve the issue.
- jeroenhd 5y ago
  You should be able to ask Lenovo for a refund if you've bought the device with this feature in mind and if Lenovo advertised the ability to watch 4K on your preferred streaming service. If the device just happens to support 4k, you may be out of luck. You could try sueing the parties that are supposed to deliver the 4k content and have revoked the key, but I doubt you'll get much out of them. If you rely on DRM, the media industry has all the keys. You're left to their whims when it comes to content consumption, and there's very little you can do.
NavinF 5y ago
Would they release a firmware update with new keys though? If they can’t fix the vulnerability, the new keys would get dumped just like the old ones.

londons_explore 5y ago

Does this mean if I have a lenovo tablet that currently streams 4K, that it will lose 4K video support? Could I ask Lenovo for a refund?

nikanj 5y ago
Yes and yes. Lenovo probably doesn’t give a shit, though. But you can ask!
- Scoundreller 5y ago
  Depends on the country. Some do have some liability on manufacturers and/or vendors for defects. Unsure if an asterisk in their click through contract about key revocation would even matter.
garblegarble 5y ago
I would think so (the repo suggests this is a Lenovo TB-X505X key, I'd imagine they're at least per-product). I could certainly be be wrong about L1 keys being burned-in, that was just my understanding of it (vendor docs say things like "Hardware DRM", but maybe I'm jumping to conclusions from marketing speak) The Widevine spec doesn't say either, it just says that all processing is within the Trusted Execution Environment, so I suppose the keys could be loaded/updated in firmware. I'm looking for more docs now... Edit: looks like I was wrong and they can be changed with firmware updates: http://bits-please.blogspot.com/2016/04/exploring-qualcomms-secure-execution.html http://bits-please.blogspot.com/2016/04/exploring-qualcomms-...
- alias_neo 5y ago
  TEE is an environment with hardware backed attestation, you run a piece of software in the "black box" to do things like key generation etc. My educated guess, having used TEE/TrustZone for keys is that they could update the payload (the "Trusted Executable") with a new one to resolve the issue.
jeroenhd 5y ago
You should be able to ask Lenovo for a refund if you've bought the device with this feature in mind and if Lenovo advertised the ability to watch 4K on your preferred streaming service. If the device just happens to support 4k, you may be out of luck. You could try sueing the parties that are supposed to deliver the 4k content and have revoked the key, but I doubt you'll get much out of them. If you rely on DRM, the media industry has all the keys. You're left to their whims when it comes to content consumption, and there's very little you can do.

NavinF 5y ago

Would they release a firmware update with new keys though? If they can’t fix the vulnerability, the new keys would get dumped just like the old ones.