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T2, FileVault and brute force attack protection

November 1, 2018 1 comment

Apple recently released an overview document for its new T2 chip, which includes how the new T2 chip-equipped Macs have new protections against brute force attacks. This protection only applies if FileVault is enabled and is similar in concept to how iOS devices set with passcodes are protected against brute force attacks.

On iOS, if an incorrect passcode is entered more than five times, a one minute delay is set.

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After the sixth try, the delay is now five minutes and the delays get longer from there until the device has the 10th wrong passcode entered and the device wipes.

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On Apple iOS devices with a Secure Enclave, those delays are enforced by the Secure Enclave processor. Similarly, the T2 chip-equipped Macs also have a Secure Enclave processor which is managing access attempts and introducing delays.

For Macs with Secure Enclave, the enforcement looks like this:

  • 30 unlock attempts via using the password at the login window or target disk mode
  • 10 unlock attempts via using the password in Recovery Mode
  • 30 unlock attempts for each enabled FileVault recovery mechanism
    • iCloud recovery
    • FileVault personal recovery key
    • FileVault institutional recovery key

The maximum number of unlock attempts is 90, regardless of the mix of methods used. After 90 attempts, the Secure Enclave processor will no longer process any requests to do the following:

  • Unlock the volume
  • Decrypt the volume
  • Verify the password / recovery key

Delays are also imposed on macOS between attempts.

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So what happens after 90 attempts? Does the Mac lock forever and become a paperweight?

After checking with AppleCare Enterprise, the answer is that the Mac will not be a paperweight, but that the Mac’s boot drive will need to be erased before it can be used again. This approach helps make sure that the Mac is still usable, but also ensures that the encrypted data stored on the boot drive is no longer recoverable.

For more information about brute force protection for encrypted iOS and macOS devices, I recommend checking out Apple’s currently available white papers:

The T2 Macs, the end of NetBoot and deploying from macOS Recovery

August 15, 2018 9 comments

In late 2017, Apple released the iMac Pro. Along with the new Secure Enclave protection provided by Apple’s T2 chip, the iMac Pro brought another notable development: It did not support booting from a network volume, otherwise known as NetBoot.

The one exception was Apple’s Internet Recovery, where Apple is providing a NetBoot-like service to provide access to macOS Recovery. The iMac Pro is still able to boot to Internet Recovery, which provides a way to repair the Mac or reinstall the operating system in situations where the Mac’s own Recovery volume is missing or not working properly.

With NetBoot not being available for the iMac Pro but still available for other models, it wasn’t yet clear if NetBoot-based workflows for setting up new Macs or rebuilding existing ones were on the way out. However, Apple’s release of of T2-equipped MacBook Pros in July 2018 which also could not use NetBoot has made Apple’s direction clear. As Apple releases new Mac models equipped with T2 chips and Secure Enclave, it is unlikely that these future Mac releases will be supporting NetBoot.

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For Mac admins using NetBoot-based workflows to set up their Macs, what are the alternatives? Apple has been encouraging the use of Apple’s Device Enrollment Program, which leverages a company, school or institutions’ mobile device management (MDM) service. In this case, you would need to arrange with Apple or an Apple reseller to purchase Macs that are enrolled in your organization’s DEP.

When a DEP-enrolled Mac is started for the first time (or started after an OS reinstall), it is automatically configured to use your organizations’ MDM service and the device checks in with the MDM service. The MDM service then configures the Mac as desired with your organization’s software and configuration settings. A good example of what this process may look like can be seen here.

What if you don’t have DEP, or you don’t have MDM? In that case, you may still be able to leverage Recovery-based deployment methods, which would allow you install the desired software and configuration settings onto the Mac’s existing OS, or install a new OS along with software and configuration settings. For more details on these methods, please see below the jump.

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Secure Enclave, Mac SSD hardware encryption and the future of FileVault

January 8, 2018 5 comments

The iMac Pro introduced a number of new features, but one that may have been little noticed is the introduction of hardware encryption for the iMac Pro’s SSD storage. Apple references the hardware encryption on the iMac Pro page this way:

T2 also makes iMac Pro even more secure, thanks to a Secure Enclave coprocessor that provides the foundation for new encrypted storage and secure boot capabilities. The data on your SSD is encrypted using dedicated AES hardware with no effect on the SSD’s performance, while keeping the Intel Xeon processor free for your compute tasks.

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This hardware encryption means that, even if FileVault is not enabled, the data stored on the iMac Pro’s SSD storage is encrypted. What’s more, the key to unlock the encryption is stored in the iMac Pro’s Secure Enclave and never leaves the machine. Physically remove the SSD storage from the iMac Pro and you won’t be able to access any data stored on the SSD, even if you have an otherwise identical iMac Pro available.

For those with knowledge of how Apple protects data stored on iOS devices, this should sound familiar. The main difference between the iOS and macOS implementation at this point appears to be that macOS does not have the equivalent passcode lock screen.

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Instead, the needed encryption key to unlock the hardware encryption is automatically provided by the Secure Enclave when the iMac Pro boots. This behavior is just like that seen on an iOS device where a passcode has not been enabled.

This is referenced when you run the following command on an iMac Pro:

diskutil apfs list

On an iMac Pro where FileVault is not enabled, FileVault is shown with the following status:

FileVault: No (Encrypted at rest)

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This recognizes that encryption is available, but that the encryption only provides protection when the data is at rest. “Data at rest” in this context should be understood to mean when the Secure Enclave has not provided the needed encryption unlock key, which would be the case in either of the following scenarios:

  1. The iMac Pro is off.
  2. The SSD storage has been removed from the iMac Pro.

For more, please see below the jump.

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