Passcodes and passwords
To protect user data from malicious attack, Apple uses passcodes in iOS and iPadOS and passwords in macOS. The longer a passcode or password is, the stronger it is—and the easier it is to discourage brute-force attacks. To further discourage attacks, Apple enforces time delays (for iOS and iPadOS) and a limited number of password attempts (for Mac).
In iOS and iPadOS, setting up a device passcode or password, the user automatically enables Data Protection. Data Protection is also enabled on other devices that feature an Apple system on chip (SoC)—such as a Mac with Apple silicon, Apple TV, and Apple Watch. In macOS, Apple uses the built-in volume encryption program FileVault.
How strong passcodes and passwords increase security
iOS and iPadOS support six-digit, four-digit, and arbitrary-length alphanumeric passcodes. Besides unlocking the device, a passcode or password provides entropy for certain encryption keys. This means an attacker in possession of a device can’t get access to data in specific protection classes without the passcode.
The passcode or password is entangled with the device’s UID, so brute-force attempts must be performed on the device under attack. A large iteration count is used to make each attempt slower. The iteration count is calibrated so that one attempt takes approximately 80 milliseconds. In fact, it would take more than five and one-half years to try all combinations of a six-character alphanumeric passcode with lowercase letters and numbers.
The stronger the user passcode is, the stronger the encryption key becomes. And by using Face ID and Touch ID, the user can establish a much stronger passcode than would otherwise be practical. The stronger passcode increases the effective amount of entropy protecting the encryption keys used for Data Protection, without adversely affecting the user experience of unlocking a device multiple times throughout the day.
If a long password that contains only numbers is entered, a numeric keypad is displayed at the Lock Screen instead of the full keyboard. A longer numeric passcode may be easier to enter than a shorter alphanumeric passcode, while providing similar security.
Users can specify a longer alphanumeric passcode by selecting Custom Alphanumeric Code in the Passcode Options in Settings > Touch ID & Passcode or Face ID & Passcode.
How escalating time delays discourage brute-force attacks (iOS, iPadOS)
In iOS and iPadOS, to further discourage brute-force passcode attacks, there are escalating time delays after the entry of an invalid passcode at the Lock Screen, as shown in the table below.
If the Erase Data option is turned on (in Settings > Touch ID & Passcode), after 10 consecutive incorrect attempts to enter the passcode, all content and settings are removed from storage. Consecutive attempts of the same incorrect passcode don’t count toward the limit. This setting is also available as an administrative policy through a mobile device management (MDM) solution that supports this feature and through Microsoft Exchange ActiveSync, and can be set to a lower threshold.
On devices with Secure Enclave, the delays are enforced by the Secure Enclave. If the device is restarted during a timed delay, the delay is still enforced, with the timer starting over for the current period.
How escalating time delays discourage brute-force attacks (macOS)
To help prevent brute-force attacks, when Mac starts up, no more than 10 password attempts are allowed at the Login Window or using Target Disk Mode, and escalating time delays are imposed after a certain number of incorrect attempts. The delays are enforced by the Secure Enclave. If Mac is restarted during a timed delay, the delay is still enforced, with the timer starting over for the current period.
The table below shows delays between password attempts on a Mac with Apple silicon and a Mac with at T2 chip.
To help prevent malware from causing permanent data loss by trying to attack the user’s password, these limits aren’t enforced after the user has successfully logged in to the Mac, but they are reimposed after reboot. If the 10 attempts are exhausted, 10 more attempts are available after booting into recoveryOS. And if those are also exhausted, then 10 additional attempts are available for each FileVault recovery mechanism (iCloud recovery, FileVault recovery key, and institutional key), for a maximum of 30 additional attempts. After those additional attempts are exhausted, the Secure Enclave no longer processes any requests to decrypt the volume or verify the password, and the data on the drive becomes unrecoverable.
To help protect data in an enterprise setting, IT should define and enforce FileVault configuration policies using an MDM solution. Organizations have several options for managing encrypted volumes, including institutional recovery keys, personal recovery keys (that can optionally be stored with MDM for escrow), or a combination of both. Key rotation can also be set as a policy in MDM.
On a Mac with the Apple T2 Security Chip, the password serves a similar function except that the key generated is used for FileVault encryption rather than Data Protection. macOS also offers additional password recovery options:
FileVault institutional key