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Seems more like short sightedness than "petty revenge." The new home button hardware can't be securely validated, and a future OS update fails on the unexpecte

Seems more like short sightedness than "petty revenge." The new home button hardware can't be securely validated, and a future OS update fails on the unexpected condition of invalid Touch ID hardware. I can imagine that this wasn't a prioritised testing scenario, likely not even considered by Apple when developing iOS. It's a lousy way to fail — the phone should just disable Touch ID and Apple Pay, and anything that relies on the secure co-processor. But it feels far more like there's an `else` branch sitting in the iOS codebase somewhere where a programmer has written: //NOTE: This should never, ever happen //.. code that triggers error 53

taspeotis 11y ago
The scenario they're protecting against appears (to me) to be a bad actor changing the hardware. If the Touch ID sensor is bad, and you propose falling back to a PIN, who's to say the digitizer isn't compromised too and is recording touches? Sounds a bit like a downgrade attack if they didn't fail fast and hard at the earliest opportunity.
- Sir_Substance 11y ago
  If I understand this correctly (not an iphone person), the touch ID sensor is just a fingerprint scanner? As a standalone measure, biometrics make a shitty password substitute because you can't change a finger print if it's compromised, so shouldn't the iphone be secured on the premise that the finger print scanner is already compromised, hence losing it should not qualify as a downgrade attack?
  - interpol_p 11y ago
    Touch ID is a fingerprint scanner, but the Touch ID system is paired with the "Secure Enclave" in Apple's AX chips. Secure Enclave is a separate coprocessor running its own L4-based microkernel. This hardware is directly paired with security-sensitive hardware (Touch ID, Apple Pay NFC chip, etc). It provides all cryptographic operations for data protection key management and maintains the integrity of data protection even if the kernel has been compromised. So when you stick a third-party Touch ID sensor in an iPhone it's obviously not going to be paired with the secure coprocessor. It doesn't really matter whether biometrics are shitty passwords, the iOS update process realises there is compromised hardware touching the Secure Enclave and fails in the worst possible way for the user.
    - Sir_Substance 11y ago
      Aha, that makes more sense.
    - nly 11y ago
      Does this mean your fingerprint never leaves the scanners coprocessor and is inaccessible to iOS and the other processors and OSs within the phone?
      - joosters 11y ago
        Yes. The OS can only tell if the fingerprint matched or not. The checking is done solely in the secure enclave. Presumably the OS also gets told which fingerprint matched too?
      - retromario 11y ago
        Yes, at least according to Apple: https://www.apple.com/business/docs/iOS_Security_Guide.pdf https://www.apple.com/business/docs/iOS_Security_Guide.pdf (page 7). "The Secure Enclave is responsible for processing fingerprint data from the Touch ID sensor, determining if there is a match against registered fingerprints, and then enabling access or purchases on behalf of the user. Communication between the processor and the Touch ID sensor takes place over a serial peripheral interface bus. The processor forwards the data to the Secure Enclave but _cannot_ read it".
      - interpol_p 11y ago
        Basically, yes. The Secure Enclave is hardware isolated from the rest of the chip. Apple's own security guide explains it best [1]: > The Secure Enclave is responsible for processing fingerprint data from the Touch ID sensor, determining if there is a match against registered ngerprints, and then enabling access or purchases on behalf of the user. Communication between the processor and the Touch ID sensor takes place over a serial peripheral interface bus. The processor forwards the data to the Secure Enclave but cannot read it. It’s encrypted and authenticated with a session key that is negotiated using the device’s shared key that is provisioned for the Touch ID sensor and the Secure Enclave. The session key exchange uses AES key wrapping with both sides providing a random key that establishes the session key and uses AES-CCM transport encryption. Regarding the actual fingerprint storage, it looks like the encryption key is kept in the Secure Enclave and the entire decryption and verification process occurs within the Secure Enclave. However the encrypted data itself may be stored outside the Secure Enclave: > The raster scan is temporarily stored in encrypted memory within the Secure Enclave while being vectorized for analysis, and then it’s discarded. The analysis utilizes sub-dermal ridge flow angle mapping, which is a lossy process that discards minutia data that would be required to reconstruct the user’s actual fingerprint. The resulting map of nodes is stored without any identity information in an encrypted format that can only be read by the Secure Enclave, and is never sent to Apple or backed up to iCloud or iTunes. [1] https://www.apple.com/business/docs/iOS_Security_Guide.pdf https://www.apple.com/business/docs/iOS_Security_Guide.pdf
- interpol_p 11y ago
  I don't think they are protecting against that scenario so much as not accounting for it. I expect Apple's assumption is that they provide all components for their devices. People who install unauthorised third party components can no longer have those devices serviced by Apple — so it no longer matters to Apple whether those devices are compromised, because they aren't really "Apple" devices at that point anyway. This botched handling of replaced hardware that hasn't been paired with the Secure Enclave ties into the above. Apple doesn't expect people to replace such hardware through a third-party, so they don't think to engineer their software to fail gracefully when it happens.
  - andromeduck 11y ago
    There's no need to be so hostile and assume malice when there's plenty of perfectly sound explanations otherwise. Apple is a fairly security conscious company now so security tradeoffs should not be a surprise.
    - interpol_p 11y ago
      Assume malice? How do you mean?
  - qb45 11y ago
    There is only one valid reason to authenticate the fingerprint scanner before using it, and that is to prevent the use of aftermarket replacements. No matter what the motives behind this mechanism were, it was put in place exactly to prevent 3rd party scanners from working. And if they implemented authentication and didn't even test what happens if it fails, then well... how do they know it works at all?
    - interpol_p 11y ago
      If you have a secure enclave within the device, then any hardware which has a direct connection to that secure enclave must be authenticated. It doesn't matter about aftermarket replacements. The entire purpose of the secure enclave is defeated if it trusts any hardware connected to it. I'm not saying they didn't test what happens when it fails. I'm saying they didn't do user testing on what happens when it fails. I'm sure the engineers tried out the hardware authentication system. They just didn't test the whole scenario once iOS was sitting on the end product. So yes, it was put in place to stop any hardware that could not be trusted from accessing users' secure data. But no, it was not done to prevent aftermarket replacements. The only reason I can see Apple caring about aftermarket replacements is because they are often low quality, and cause customers to go back to Apple with unauthorised repairs. (I've witnessed this more than once in an Apple store, someone coming in who had their screen replaced outside Apple and the touch digitiser was failing. Apple just sends them away.)
- qb45 11y ago
  > If the Touch ID sensor is bad, and you propose falling back to a PIN, who's to say the digitizer isn't compromised too and is recording touches? So why not brick the phone out of the box? Even if the finger scanner is original, somebody may have compromised the digitizer anyway.
Reason077 11y ago
There's a lot of stuff that depends on the secure element - in fact the phone would be quite useless without it. In fact, when you first reboot your phone, even contacts cannot be accessed until you authenticate with your passcode to unlock the secure element. Incoming text messages only show the phone number. You're right, however - a Touch ID sensor that cannot be verified should not brick the phone. Apple should just disable Touch ID and sever any link between the sensor and the secure element.
- brador 11y ago
  The issue is Apple cannot verify a secure touch ID replacement over a compromised touch ID replacement. Without knowing if your replacement is secure the change potentially compromises the security of the whole device. IMO bricking on touch ID issues is extreme, but maximises the security of the device.
  - izacus 11y ago
    How? TouchID is the less secure authentication than password/PIN anyway (which is shown by the fact that you need to enter PIN/Pass right after boot). How would just disabling TouchID auth be a worse option?
    - coldtea 11y ago
      >TouchID is the less secure authentication than password/PIN anyway (which is shown by the fact that you need to enter PIN/Pass right after boot). The fact that you need to enter PIN right after boot, just shows that they use "two factor authentication" to make it even more secure. It doesn't IN ANY WAY show that TouchID is "the less secure authentication" method of the two.
      - germanier 11y ago
        You can do anything you want on the phone without using Touch ID at all. The fingerprint sensor is not a necessary factor in their implementation, while the passcode is.
DonHopkins 11y ago
Too bad the compiler doesn't raise a fatal error for comments like that.
deleted 11y ago
[deleted]

taspeotis 11y ago

The scenario they're protecting against appears (to me) to be a bad actor changing the hardware. If the Touch ID sensor is bad, and you propose falling back to a PIN, who's to say the digitizer isn't compromised too and is recording touches? Sounds a bit like a downgrade attack if they didn't fail fast and hard at the earliest opportunity.

Sir_Substance 11y ago
If I understand this correctly (not an iphone person), the touch ID sensor is just a fingerprint scanner? As a standalone measure, biometrics make a shitty password substitute because you can't change a finger print if it's compromised, so shouldn't the iphone be secured on the premise that the finger print scanner is already compromised, hence losing it should not qualify as a downgrade attack?
- interpol_p 11y ago
  Touch ID is a fingerprint scanner, but the Touch ID system is paired with the "Secure Enclave" in Apple's AX chips. Secure Enclave is a separate coprocessor running its own L4-based microkernel. This hardware is directly paired with security-sensitive hardware (Touch ID, Apple Pay NFC chip, etc). It provides all cryptographic operations for data protection key management and maintains the integrity of data protection even if the kernel has been compromised. So when you stick a third-party Touch ID sensor in an iPhone it's obviously not going to be paired with the secure coprocessor. It doesn't really matter whether biometrics are shitty passwords, the iOS update process realises there is compromised hardware touching the Secure Enclave and fails in the worst possible way for the user.
  - Sir_Substance 11y ago
    Aha, that makes more sense.
  - nly 11y ago
    Does this mean your fingerprint never leaves the scanners coprocessor and is inaccessible to iOS and the other processors and OSs within the phone?
    - joosters 11y ago
      Yes. The OS can only tell if the fingerprint matched or not. The checking is done solely in the secure enclave. Presumably the OS also gets told which fingerprint matched too?
    - retromario 11y ago
      Yes, at least according to Apple: https://www.apple.com/business/docs/iOS_Security_Guide.pdf https://www.apple.com/business/docs/iOS_Security_Guide.pdf (page 7). "The Secure Enclave is responsible for processing fingerprint data from the Touch ID sensor, determining if there is a match against registered fingerprints, and then enabling access or purchases on behalf of the user. Communication between the processor and the Touch ID sensor takes place over a serial peripheral interface bus. The processor forwards the data to the Secure Enclave but _cannot_ read it".
    - interpol_p 11y ago
      Basically, yes. The Secure Enclave is hardware isolated from the rest of the chip. Apple's own security guide explains it best [1]: > The Secure Enclave is responsible for processing fingerprint data from the Touch ID sensor, determining if there is a match against registered ngerprints, and then enabling access or purchases on behalf of the user. Communication between the processor and the Touch ID sensor takes place over a serial peripheral interface bus. The processor forwards the data to the Secure Enclave but cannot read it. It’s encrypted and authenticated with a session key that is negotiated using the device’s shared key that is provisioned for the Touch ID sensor and the Secure Enclave. The session key exchange uses AES key wrapping with both sides providing a random key that establishes the session key and uses AES-CCM transport encryption. Regarding the actual fingerprint storage, it looks like the encryption key is kept in the Secure Enclave and the entire decryption and verification process occurs within the Secure Enclave. However the encrypted data itself may be stored outside the Secure Enclave: > The raster scan is temporarily stored in encrypted memory within the Secure Enclave while being vectorized for analysis, and then it’s discarded. The analysis utilizes sub-dermal ridge flow angle mapping, which is a lossy process that discards minutia data that would be required to reconstruct the user’s actual fingerprint. The resulting map of nodes is stored without any identity information in an encrypted format that can only be read by the Secure Enclave, and is never sent to Apple or backed up to iCloud or iTunes. [1] https://www.apple.com/business/docs/iOS_Security_Guide.pdf https://www.apple.com/business/docs/iOS_Security_Guide.pdf
interpol_p 11y ago
I don't think they are protecting against that scenario so much as not accounting for it. I expect Apple's assumption is that they provide all components for their devices. People who install unauthorised third party components can no longer have those devices serviced by Apple — so it no longer matters to Apple whether those devices are compromised, because they aren't really "Apple" devices at that point anyway. This botched handling of replaced hardware that hasn't been paired with the Secure Enclave ties into the above. Apple doesn't expect people to replace such hardware through a third-party, so they don't think to engineer their software to fail gracefully when it happens.
- andromeduck 11y ago
  There's no need to be so hostile and assume malice when there's plenty of perfectly sound explanations otherwise. Apple is a fairly security conscious company now so security tradeoffs should not be a surprise.
  - interpol_p 11y ago
    Assume malice? How do you mean?
- qb45 11y ago
  There is only one valid reason to authenticate the fingerprint scanner before using it, and that is to prevent the use of aftermarket replacements. No matter what the motives behind this mechanism were, it was put in place exactly to prevent 3rd party scanners from working. And if they implemented authentication and didn't even test what happens if it fails, then well... how do they know it works at all?
  - interpol_p 11y ago
    If you have a secure enclave within the device, then any hardware which has a direct connection to that secure enclave must be authenticated. It doesn't matter about aftermarket replacements. The entire purpose of the secure enclave is defeated if it trusts any hardware connected to it. I'm not saying they didn't test what happens when it fails. I'm saying they didn't do user testing on what happens when it fails. I'm sure the engineers tried out the hardware authentication system. They just didn't test the whole scenario once iOS was sitting on the end product. So yes, it was put in place to stop any hardware that could not be trusted from accessing users' secure data. But no, it was not done to prevent aftermarket replacements. The only reason I can see Apple caring about aftermarket replacements is because they are often low quality, and cause customers to go back to Apple with unauthorised repairs. (I've witnessed this more than once in an Apple store, someone coming in who had their screen replaced outside Apple and the touch digitiser was failing. Apple just sends them away.)
qb45 11y ago
> If the Touch ID sensor is bad, and you propose falling back to a PIN, who's to say the digitizer isn't compromised too and is recording touches? So why not brick the phone out of the box? Even if the finger scanner is original, somebody may have compromised the digitizer anyway.

Reason077 11y ago

There's a lot of stuff that depends on the secure element - in fact the phone would be quite useless without it. In fact, when you first reboot your phone, even contacts cannot be accessed until you authenticate with your passcode to unlock the secure element. Incoming text messages only show the phone number. You're right, however - a Touch ID sensor that cannot be verified should not brick the phone. Apple should just disable Touch ID and sever any link between the sensor and the secure element.

brador 11y ago
The issue is Apple cannot verify a secure touch ID replacement over a compromised touch ID replacement. Without knowing if your replacement is secure the change potentially compromises the security of the whole device. IMO bricking on touch ID issues is extreme, but maximises the security of the device.
- izacus 11y ago
  How? TouchID is the less secure authentication than password/PIN anyway (which is shown by the fact that you need to enter PIN/Pass right after boot). How would just disabling TouchID auth be a worse option?
  - coldtea 11y ago
    >TouchID is the less secure authentication than password/PIN anyway (which is shown by the fact that you need to enter PIN/Pass right after boot). The fact that you need to enter PIN right after boot, just shows that they use "two factor authentication" to make it even more secure. It doesn't IN ANY WAY show that TouchID is "the less secure authentication" method of the two.
    - germanier 11y ago
      You can do anything you want on the phone without using Touch ID at all. The fingerprint sensor is not a necessary factor in their implementation, while the passcode is.

DonHopkins 11y ago

Too bad the compiler doesn't raise a fatal error for comments like that.

deleted 11y ago

[deleted]