3 ms·

Is it possible to change a phone's device id to match the initial target, though?

by theoh 11y ago

KMag 11y ago
I believe the FBI is suggesting that Apple tie the update to the phone's IMEI, which I believe phone thieves routinely change by desoldering and replacing a chip.
- ryanlol 11y ago
  Apple firmware updates are signed on a per-install basis.
  - ryanlol 11y ago
    Not sure why this got downvoted, I'm not too familiar with iOS but AFAIK this is exactly how the SHSH system works with the modern iPhones. Quick googling seems to support this.
    - KMag 11y ago
      I didn't downvote you, but I think you're being downvoted because the information content isn't much more than "but cryptography something something!" I mentioned that the most common method for uniquely identifying a handset (the IMEI) can be changed by switching a chip on the iPhone's main board. (At least this was true 6 years ago.) So, unless Apple uses an interactive signature scheme or prevents the FBI/intelligence agencies from ever seeing the signature (using TLS with hard-coded certs), then the signature can be replayed. If the signature can be replayed, then in order to prevent FBiOS being used on multiple phones, it must be tied to one or more unique identifiers, probably excluding the IMEI. Many people understood my post as shorthand for the above. Responding to this with "[But] Apple firmware updates are signed on a per-install basis." doesn't add to the conversation unless you provide further details. At least, that's my best guess as to why you've been downvoted.
      - ryanlol 11y ago
        >I mentioned that the most common method for uniquely identifying a handset (the IMEI) can be changed by switching a chip on the iPhone's main board. (At least this was true 6 years ago.) https://www.theiphonewiki.com/wiki/ECID https://www.theiphonewiki.com/wiki/ECID Firmware updates use this, not IMEIs. And I think the IMEI is more commonly used to identify the radio, not the device itself. But I could be wrong about that. >So, unless Apple uses an interactive signature scheme or prevents the FBI/intelligence agencies from ever seeing the signature (using TLS with hard-coded certs), then the signature can be replayed. Every time you update an iPhone it generates a nonce, called APTicket. Apple signs that, your ECID and the firmware. The nonce essentially makes replay attacks impossible, even if you managed to swap a devices ECID.
        KMag 11y ago
        Thanks for the research! If they're signing the ECID using an interactive signature algorithm, then it sounds like they've thought it through pretty well. > And I think the IMEI is more commonly used to identify the radio, not the device itself. Across manufactures, I'm not sure another quasi-unique identifier in common use. > Every time you update an iPhone it generates a nonce, called APTicket. Apple signs that, your ECID and the firmware. This is one variant of interactive signature scheme.

Is it possible to change a phone's device id to match the initial target, though?

by theoh 11y ago

Is it possible to change a phone's device id to match the initial target, though?

KMag 11y ago

I believe the FBI is suggesting that Apple tie the update to the phone's IMEI, which I believe phone thieves routinely change by desoldering and replacing a chip.

ryanlol 11y ago
Apple firmware updates are signed on a per-install basis.
- ryanlol 11y ago
  Not sure why this got downvoted, I'm not too familiar with iOS but AFAIK this is exactly how the SHSH system works with the modern iPhones. Quick googling seems to support this.
  - KMag 11y ago
    I didn't downvote you, but I think you're being downvoted because the information content isn't much more than "but cryptography something something!" I mentioned that the most common method for uniquely identifying a handset (the IMEI) can be changed by switching a chip on the iPhone's main board. (At least this was true 6 years ago.) So, unless Apple uses an interactive signature scheme or prevents the FBI/intelligence agencies from ever seeing the signature (using TLS with hard-coded certs), then the signature can be replayed. If the signature can be replayed, then in order to prevent FBiOS being used on multiple phones, it must be tied to one or more unique identifiers, probably excluding the IMEI. Many people understood my post as shorthand for the above. Responding to this with "[But] Apple firmware updates are signed on a per-install basis." doesn't add to the conversation unless you provide further details. At least, that's my best guess as to why you've been downvoted.
    - ryanlol 11y ago
      >I mentioned that the most common method for uniquely identifying a handset (the IMEI) can be changed by switching a chip on the iPhone's main board. (At least this was true 6 years ago.) https://www.theiphonewiki.com/wiki/ECID https://www.theiphonewiki.com/wiki/ECID Firmware updates use this, not IMEIs. And I think the IMEI is more commonly used to identify the radio, not the device itself. But I could be wrong about that. >So, unless Apple uses an interactive signature scheme or prevents the FBI/intelligence agencies from ever seeing the signature (using TLS with hard-coded certs), then the signature can be replayed. Every time you update an iPhone it generates a nonce, called APTicket. Apple signs that, your ECID and the firmware. The nonce essentially makes replay attacks impossible, even if you managed to swap a devices ECID.
      - KMag 11y ago
        Thanks for the research! If they're signing the ECID using an interactive signature algorithm, then it sounds like they've thought it through pretty well. > And I think the IMEI is more commonly used to identify the radio, not the device itself. Across manufactures, I'm not sure another quasi-unique identifier in common use. > Every time you update an iPhone it generates a nonce, called APTicket. Apple signs that, your ECID and the firmware. This is one variant of interactive signature scheme.