5 ms·

Just goes to show that the DRM is just security through obscurity.

by trollied 4y ago

klodolph 4y ago
True for Widevine L3, which is what the article is talking about. Not true in general, and not true for L2 or L1.
- babypuncher 4y ago
  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
- no_time 4y ago
  I'd argue the same goes for L1 and L2. But the obscurity is provided by the silicon packaging process. Would be nice to crowdfund a lab to break these hardware backed treachery schemes.
  - klodolph 4y ago
    When you say “security through obscurity” there’s a certain understanding that we’re drawing a line between implementation secrecy (obscurity / obfuscation) and key secrecy. If we extend the word “obscurity” to include the notion of physical security, I think we’ve gone too far—even if physical security is just the physical security of a secret embedded in silicon that you have physical access to (because it is super difficult to recover secrets from silicon).
    - the8472 4y ago
      With DRM the user who owns the machine is the "attacker". The keys have already been handed to the user, he only needs to get them out. This is like hiding an API key in a public website's javascript with rot13. Very much security by obscurity. Proper security means that the attacker should never be in possession of the key.
      - klodolph 4y ago
        You’re saying that a hardware security module is like rot13? When you say the attacker “only” needs to get them out, the “only” is doing a lot of work, there.
        yipbub 4y ago
        Yes, but it only has to be done once.
        the8472 4y ago
        The standard for cryptographic security is that the attacker can do no better than brute force. And the complexity for that is usually set high enough that it is out of range for the entire computational capacity of our civilization for years to come. I'd say handing the key to the attacker in a package that requires somewhere between a skilled reverse-engineer and a semiconductor lab to untangle falls far short of that standard.
- Retr0id 4y ago
  I believe that L2 would be weaker than L3 in practice, which likely explains why I've also never seen it implemented (If you know about an L2 instance I would be genuinely interested in taking a look)
  - calgarymicro 4y ago
    > I believe that L2 would be weaker than L3 in practice How come?
    - Retr0id 4y ago
      According to the descriptions I can find, L2 does cryptography in secure hardware, but video decoding in software. (as opposed to L3 that does both in software, and L1 that does both in hardware). In L3, you can obfuscate the cryptography and the video codecs together as a unit, blurring any defined border between them. A determined reverse-engineer can inevitably unravel that obfuscation, but it's non-trivial. In L2, there must be some interface between the hardware and software components. That interface presents itself as a very obvious weak point. As an attacker, all you'd have to do is watch the data flowing out of the cryptography hardware, and into the video decoder software, and you'd be able to siphon out the plaintext video data. (To be clear, this is entirely "in theory" because I've never seen an L2 implementation)
socRate35 4y ago
The “security through obscurity” chant needs to die. It’s such a generalized concept it applies too broadly. Encryption is “security through obscurity”. Having few admins is security through obscurity; a guessing game of who is the admin?
deleted 4y ago
[deleted]
compsciphd 4y ago
security through obscurity is generally not about keeping a well known encryption scheme's keys "private". It's generally about not knowing how a system works at all. In this case (and the same for blurays actually), we know exactly how the system works, given the keys we could decrypt the content, but the keys are kept "well" protected (depending on widevine level, different levels of protection). In BluRay land enough player keys have leaked to make it basically irrelevant. It's also harder to determine whose keys are being used to decrypt, making it harder to revoke. In an online widevine world where one has to use one's baked in device keys to get the content key, its much easier to determine if a single device's key is being used an abnormal amount of time and then revoke it. while one can view the efforts to protect a widevine l3 key as security through obscurity, its mostly there to make the effort hard enough that most people are interested in doing it, than to keep it perfectly secure.

Just goes to show that the DRM is just security through obscurity.

klodolph 4y ago

True for Widevine L3, which is what the article is talking about. Not true in general, and not true for L2 or L1.

babypuncher 4y ago
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
no_time 4y ago
I'd argue the same goes for L1 and L2. But the obscurity is provided by the silicon packaging process. Would be nice to crowdfund a lab to break these hardware backed treachery schemes.
- klodolph 4y ago
  When you say “security through obscurity” there’s a certain understanding that we’re drawing a line between implementation secrecy (obscurity / obfuscation) and key secrecy. If we extend the word “obscurity” to include the notion of physical security, I think we’ve gone too far—even if physical security is just the physical security of a secret embedded in silicon that you have physical access to (because it is super difficult to recover secrets from silicon).
  - the8472 4y ago
    With DRM the user who owns the machine is the "attacker". The keys have already been handed to the user, he only needs to get them out. This is like hiding an API key in a public website's javascript with rot13. Very much security by obscurity. Proper security means that the attacker should never be in possession of the key.
    - klodolph 4y ago
      You’re saying that a hardware security module is like rot13? When you say the attacker “only” needs to get them out, the “only” is doing a lot of work, there.
      - yipbub 4y ago
        Yes, but it only has to be done once.
      - the8472 4y ago
        The standard for cryptographic security is that the attacker can do no better than brute force. And the complexity for that is usually set high enough that it is out of range for the entire computational capacity of our civilization for years to come. I'd say handing the key to the attacker in a package that requires somewhere between a skilled reverse-engineer and a semiconductor lab to untangle falls far short of that standard.
Retr0id 4y ago
I believe that L2 would be weaker than L3 in practice, which likely explains why I've also never seen it implemented (If you know about an L2 instance I would be genuinely interested in taking a look)
- calgarymicro 4y ago
  > I believe that L2 would be weaker than L3 in practice How come?
  - Retr0id 4y ago
    According to the descriptions I can find, L2 does cryptography in secure hardware, but video decoding in software. (as opposed to L3 that does both in software, and L1 that does both in hardware). In L3, you can obfuscate the cryptography and the video codecs together as a unit, blurring any defined border between them. A determined reverse-engineer can inevitably unravel that obfuscation, but it's non-trivial. In L2, there must be some interface between the hardware and software components. That interface presents itself as a very obvious weak point. As an attacker, all you'd have to do is watch the data flowing out of the cryptography hardware, and into the video decoder software, and you'd be able to siphon out the plaintext video data. (To be clear, this is entirely "in theory" because I've never seen an L2 implementation)

socRate35 4y ago

The “security through obscurity” chant needs to die. It’s such a generalized concept it applies too broadly. Encryption is “security through obscurity”. Having few admins is security through obscurity; a guessing game of who is the admin?

deleted 4y ago

[deleted]

compsciphd 4y ago

security through obscurity is generally not about keeping a well known encryption scheme's keys "private". It's generally about not knowing how a system works at all. In this case (and the same for blurays actually), we know exactly how the system works, given the keys we could decrypt the content, but the keys are kept "well" protected (depending on widevine level, different levels of protection). In BluRay land enough player keys have leaked to make it basically irrelevant. It's also harder to determine whose keys are being used to decrypt, making it harder to revoke. In an online widevine world where one has to use one's baked in device keys to get the content key, its much easier to determine if a single device's key is being used an abnormal amount of time and then revoke it. while one can view the efforts to protect a widevine l3 key as security through obscurity, its mostly there to make the effort hard enough that most people are interested in doing it, than to keep it perfectly secure.