The briefing with engineers was highly technical and comes as Apple is at odds with the U.S. government over the importance of device security. The FBI and other government organizations want Apple to build a backdoor into their devices.
Apple engineers said that protection starts with the Boot ROM, or memory chip, that includes a certificate that only Apple has access to. If a hacker tried to modify iOS to run their own code, the software wouldn't run because they wouldn't have access to the secret key. This applies to the iPhone 3GS and newer devices.
The boot chain ensures that the certificate or key is validated before the boot process begins. Since there is relative few lines of code at the boot level, the chances of finding a bug and exploiting it are very very low.
Apple also stresses how important iOS updates and their high adoption rate is for security. Smaller updates and the 'while you were sleeping' update option has resulted in an update rate of 80% for iOS 9.
Encryption also plays an important role in device security. Apple uses hardware between its flash memory and RAM to perform encryption and since the iPhone 5s it has utilized a 'Secure Enclave' that uses encrypted memory and can't be accessed by other parts of the device.
The introduction of Touch ID has also helped Apple secure devices by requiring the creation of a passcode in order to enable the feature.
Notably, it was the passcode feature that the FBI managed to circumvent to gain access to an iPhone 5c used by one of the San Bernardino shooters. The Washington Post reports that hackers were able to "create a piece of hardware ... to crack the iPhone's four-digit personal identification number without triggering a security feature that would have erased all the data."
Apple's press briefing comes ahead of another Congressional hearing next week where it will again present its case for encryption and device security.
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