What appears to be the decryption key for Apple's Secure Enclave Processor (SEP) firmware was posted online by a hacker going by the name of xerub.
A coprocessor fabricated in the Apple S2, Apple A7, and later A-series CPUs, SEP uses encrypted memory, has a hardware random number generator and “provides all cryptographic operations for Data Protection key management and maintains the integrity of Data Protection even if the kernel has been compromised,” Apple explains in the iOS Security Guide.
At startup, the device creates an ephemeral key entangled with the UID (Unique ID), and uses it to encrypt the Secure Enclave’s portion of memory space. The key is also used to authenticate the Secure Enclave (except on Apple A7). Apple also explains that data “saved to the file system by the Secure Enclave is encrypted with a key entangled with the UID and an anti-replay counter.”
SEP uses its own secure boot and securely generates the UID on A9 or later A-series processors. Because SEP handles Touch ID transactions, password verification, and other security processes, along with the generation of the device's UID, it is critical to iOS’ security and the public availability of the decryption key could spell disaster.
Despite publishing the decryption key (tools needed to decrypt the key are available in this GitHub repository, while those needed to process it are available in this one), xerub didn’t provide details on the decryption process.
The availability of the key, however, doesn’t appear to affect the overall security of the enclave, and even the hacker suggested that SEP doesn’t add much to security, despite its “black box” design. While the key would allow for the decryption of the firmware, it wouldn’t provide access to user data.
While researchers could only speculate what was happening inside the Secure Enclave until now, the availability of this key could shed some more light into the matter. In addition to security researchers, hackers too could start looking for vulnerabilities in SEP, in an attempt to devise new exploits to bypass authentication or generate fraudulent transactions.
SecurityWeek has contacted Apple for a comment on this and will update the story if a response arrives.
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