3 ms·

Looking the bottom part, is APRR the only mitigation exclusive to Apples own CPUs? Also, is trustzone not available on these?

RL_Quine 6y ago
There's no trustzone, no, but boot is completely verified in much stronger ways. Software updates are uniquely signed per device, per execution to prevent downgrade attacks.
- q3k 6y ago
  TrustZone is orthogonal to secure boot. It's close to functionality to SGX, trying to allow for some SecureElement-like functionality on the main SoC (in which you can do crypto, DRM, etc).
  - panpanna 6y ago
    Just a tiny remark: I think trustzone is mostly used for drm these days, SE has its own dedicated security processor on Qualcomm and (iirc) Huawei socs
- panpanna 6y ago
  This confused me. How does these unique signatures work and how does it improve boot security?
  - ghostpepper 6y ago
    IIRC the general idea is that the pin code or password is required to be entered when an update is requested, which unlocks a key pair. The public key is included in the update request, which is then sent to Apple. Apple sends back a download that is signed in a way that the firmware can verify, and Apple guarantees never to send another download in response to that exact request. This protection also relies on the secure enclave never authorizing the installation of an unsigned OS update.
    - runeks 6y ago
      > Apple sends back a download that is signed in a way that the firmware can verify, and Apple guarantees never to send another download in response to that exact request. Interesting! Thank you for the detailed explanation.
  - dbuder 6y ago
    Each device has a code, the manufacturer knows the code for each device and what device is being updated and the firmware is modified to need that code to update/work. It is more secure because if you crack the code you only have it cracked for one device - which is still bad but it is less likely to lead to an exploit that bricks all the devices.
saagarjha 6y ago
I think KTRR is also something they’ve designed themselves. Or at least, I don’t think anyone is shipping anything comparable at the moment.

RL_Quine 6y ago

There's no trustzone, no, but boot is completely verified in much stronger ways. Software updates are uniquely signed per device, per execution to prevent downgrade attacks.

q3k 6y ago
TrustZone is orthogonal to secure boot. It's close to functionality to SGX, trying to allow for some SecureElement-like functionality on the main SoC (in which you can do crypto, DRM, etc).
- panpanna 6y ago
  Just a tiny remark: I think trustzone is mostly used for drm these days, SE has its own dedicated security processor on Qualcomm and (iirc) Huawei socs
panpanna 6y ago
This confused me. How does these unique signatures work and how does it improve boot security?
- ghostpepper 6y ago
  IIRC the general idea is that the pin code or password is required to be entered when an update is requested, which unlocks a key pair. The public key is included in the update request, which is then sent to Apple. Apple sends back a download that is signed in a way that the firmware can verify, and Apple guarantees never to send another download in response to that exact request. This protection also relies on the secure enclave never authorizing the installation of an unsigned OS update.
  - runeks 6y ago
    > Apple sends back a download that is signed in a way that the firmware can verify, and Apple guarantees never to send another download in response to that exact request. Interesting! Thank you for the detailed explanation.
- dbuder 6y ago
  Each device has a code, the manufacturer knows the code for each device and what device is being updated and the firmware is modified to need that code to update/work. It is more secure because if you crack the code you only have it cracked for one device - which is still bad but it is less likely to lead to an exploit that bricks all the devices.

saagarjha 6y ago

I think KTRR is also something they’ve designed themselves. Or at least, I don’t think anyone is shipping anything comparable at the moment.