5 ms·

At the end of the day, the user's hardware/software has to be given a decryption key for the content, and the DRM scheme is all about obfuscating that encryptio

At the end of the day, the user's hardware/software has to be given a decryption key for the content, and the DRM scheme is all about obfuscating that encryption key so that users can't find it.

klodolph 4y ago
I’d say that a key stored on hardware is not merely obfuscated, when that hardware is designed to prevent you from recovering the key.
- Nextgrid 4y ago
  The hardware ultimately has to decrypt and play the content, so you can use it as a decryption oracle even if you can't extract the key itself.
  - klodolph 4y ago
    Sort of, within constraints. L1 both decrypts and decodes, so you can’t really use it as a pure decryption oracle, but it doesn’t matter if you’re going to re-encode it anyway. Not that it really matters, since HDCP has been cracked. There are a lot of holes here and a lot of problems with DRM.
mardifoufs 4y ago
Eehhh at the end of the day, L1 is still almost impossible to bypass and hasn't been broken in years. So it still works, meaning it doesn't really matter even if it's security by obscurity (I dont think it qualifies for the term but anyways).
- grishka 4y ago
  If it hasn't been broken, then where do all those 4K HDR torrents come from?
  - judge2020 4y ago
    Nvidia Shield[0] 0: https://forum.xda-developers.com/t/nvidia-shield-pro-widevine-keys-extraction-and-re-flashing.4203089/ https://forum.xda-developers.com/t/nvidia-shield-pro-widevin...
  - DeathArrow 4y ago
    From cracked HDMI HDCP?
- dublinben 4y ago
  Circumventing higher levels of Widevine has been unnecessary until now, since the HDCP protecting the inevitable HDMI video output has been thoroughly cracked. Pristine 1080p and 4k copies of Netflix content is widely available.
  - loeg 4y ago
    > since the HDCP protecting the inevitable HDMI video output has been thoroughly cracked My impression is the stuff coming from the various streaming services is not captured and reencoded, but direct bit-for-bit copy of the original H.264 (or H.265) encoding (sans DRM). (Yeah, others will do reencodes later but quite a bit of the source material encoding comes directly from the streaming sites.)
    - dublinben 4y ago
      You're right that there is plenty of directly stream-ripped content out there, presumably using cracks of various levels of Widevine. The makers of these tools and the groups using them tend to keep quiet about the details of the precise exploits they're using, for obvious reasons. Ultimately, there's no shortage of DRM-free 4K content, whether from streaming services or Blu-Ray, since there's always a weak point in the chain somewhere.
      - loeg 4y ago
        Yeah. With blurays, you can always extract the device key out of some Bluray player. It's an extremely poor user experience for bluray consumers to have their devices stop working for new movies, so my impression is these keys aren't blacklisted all that quickly. For the streaming sites, I have no idea. But, yeah, the cleartext bits need to get in front of the user eventually.
        mike_hearn 4y ago
        BluRay has two security systems. One is based on key revocation (AACS) and one is based on embedding programs written by companies contracted by the movie studios which do dynamic detection of rippers. AACS failed almost immediately because indeed, keys leaked faster than they could be revoked. BD+ proved much harder, at least in the early years. But it was only ever designed to last about 10 years according even to the sales pitch of the designers and it's older than that now, so I wouldn't expect it to be all that effective anymore especially since Intel pulled SGX from their client chips.
- a257 4y ago
  L1 has been bypassed by piracy groups for years (through social engineering). They just don't share the keys publicly because it would give their opponents an advantage. See [1]. [1] https://news.ycombinator.com/item?id=29702110 https://news.ycombinator.com/item?id=29702110
  - mardifoufs 4y ago
    True, I didn't realize those were l1 keys. I'll have to read up on the revocation mechanism, if there is any. I'm also wondering how those keys usually leak. Is it through vulns, or just exploiting unsecure key handling?
    - GOATS- 4y ago
      The Nexus 6's L1 keys were dumped through a vulnerability in Qualcomm's trusted code execution environment. http://bits-please.blogspot.com/2016/05/qsee-privilege-escalation-vulnerability.html http://bits-please.blogspot.com/2016/05/qsee-privilege-escal... https://googleprojectzero.blogspot.com/2017/07/trust-issues-exploiting-trustzone-tees.html https://googleprojectzero.blogspot.com/2017/07/trust-issues-...

At the end of the day, the user's hardware/software has to be given a decryption key for the content, and the DRM scheme is all about obfuscating that encryption key so that users can't find it.

klodolph 4y ago

I’d say that a key stored on hardware is not merely obfuscated, when that hardware is designed to prevent you from recovering the key.

Nextgrid 4y ago
The hardware ultimately has to decrypt and play the content, so you can use it as a decryption oracle even if you can't extract the key itself.
- klodolph 4y ago
  Sort of, within constraints. L1 both decrypts and decodes, so you can’t really use it as a pure decryption oracle, but it doesn’t matter if you’re going to re-encode it anyway. Not that it really matters, since HDCP has been cracked. There are a lot of holes here and a lot of problems with DRM.

mardifoufs 4y ago

Eehhh at the end of the day, L1 is still almost impossible to bypass and hasn't been broken in years. So it still works, meaning it doesn't really matter even if it's security by obscurity (I dont think it qualifies for the term but anyways).

grishka 4y ago
If it hasn't been broken, then where do all those 4K HDR torrents come from?
- judge2020 4y ago
  Nvidia Shield[0] 0: https://forum.xda-developers.com/t/nvidia-shield-pro-widevine-keys-extraction-and-re-flashing.4203089/ https://forum.xda-developers.com/t/nvidia-shield-pro-widevin...
- DeathArrow 4y ago
  From cracked HDMI HDCP?
dublinben 4y ago
Circumventing higher levels of Widevine has been unnecessary until now, since the HDCP protecting the inevitable HDMI video output has been thoroughly cracked. Pristine 1080p and 4k copies of Netflix content is widely available.
- loeg 4y ago
  > since the HDCP protecting the inevitable HDMI video output has been thoroughly cracked My impression is the stuff coming from the various streaming services is not captured and reencoded, but direct bit-for-bit copy of the original H.264 (or H.265) encoding (sans DRM). (Yeah, others will do reencodes later but quite a bit of the source material encoding comes directly from the streaming sites.)
  - dublinben 4y ago
    You're right that there is plenty of directly stream-ripped content out there, presumably using cracks of various levels of Widevine. The makers of these tools and the groups using them tend to keep quiet about the details of the precise exploits they're using, for obvious reasons. Ultimately, there's no shortage of DRM-free 4K content, whether from streaming services or Blu-Ray, since there's always a weak point in the chain somewhere.
    - loeg 4y ago
      Yeah. With blurays, you can always extract the device key out of some Bluray player. It's an extremely poor user experience for bluray consumers to have their devices stop working for new movies, so my impression is these keys aren't blacklisted all that quickly. For the streaming sites, I have no idea. But, yeah, the cleartext bits need to get in front of the user eventually.
      - mike_hearn 4y ago
        BluRay has two security systems. One is based on key revocation (AACS) and one is based on embedding programs written by companies contracted by the movie studios which do dynamic detection of rippers. AACS failed almost immediately because indeed, keys leaked faster than they could be revoked. BD+ proved much harder, at least in the early years. But it was only ever designed to last about 10 years according even to the sales pitch of the designers and it's older than that now, so I wouldn't expect it to be all that effective anymore especially since Intel pulled SGX from their client chips.
a257 4y ago
L1 has been bypassed by piracy groups for years (through social engineering). They just don't share the keys publicly because it would give their opponents an advantage. See [1]. [1] https://news.ycombinator.com/item?id=29702110 https://news.ycombinator.com/item?id=29702110
- mardifoufs 4y ago
  True, I didn't realize those were l1 keys. I'll have to read up on the revocation mechanism, if there is any. I'm also wondering how those keys usually leak. Is it through vulns, or just exploiting unsecure key handling?
  - GOATS- 4y ago
    The Nexus 6's L1 keys were dumped through a vulnerability in Qualcomm's trusted code execution environment. http://bits-please.blogspot.com/2016/05/qsee-privilege-escalation-vulnerability.html http://bits-please.blogspot.com/2016/05/qsee-privilege-escal... https://googleprojectzero.blogspot.com/2017/07/trust-issues-exploiting-trustzone-tees.html https://googleprojectzero.blogspot.com/2017/07/trust-issues-...