Recovering an iPhone 5c Passcode

Remember the San Bernardino killer’s iPhone, and how the FBI maintained that they couldn’t get the encryption key without Apple providing them with a universal backdoor? Many of us computer-security experts said that they were wrong, and there were several possible techniques they could use. One of them was manually removing the flash chip from the phone, extracting the memory, and then running a brute-force attack without worrying about the phone deleting the key.

The FBI said it was impossible. We all said they were wrong. Now, Sergei Skorobogatov has proved them wrong. Here’s his paper:

Abstract: This paper is a short summary of a real world mirroring attack on the Apple iPhone 5c passcode retry counter under iOS 9. This was achieved by desoldering the NAND Flash chip of a sample phone in order to physically access its connection to the SoC and partially reverse engineering its proprietary bus protocol. The process does not require any expensive and sophisticated equipment. All needed parts are low cost and were obtained from local electronics distributors. By using the described and successful hardware mirroring process it was possible to bypass the limit on passcode retry attempts. This is the first public demonstration of the working prototype and the real hardware mirroring process for iPhone 5c. Although the process can be improved, it is still a successful proof-of-concept project. Knowledge of the possibility of mirroring will definitely help in designing systems with better protection. Also some reliability issues related to the NAND memory allocation in iPhone 5c are revealed. Some future research directions are outlined in this paper and several possible countermeasures are suggested. We show that claims that iPhone 5c NAND mirroring was infeasible were ill-advised.

Susan Landau explains why this is important:

The moral of the story? It’s not, as the FBI has been requesting, a bill to make it easier to access encrypted communications, as in the proposed revised Burr-Feinstein bill. Such “solutions” would make us less secure, not more so. Instead we need to increase law enforcement’s capabilities to handle encrypted communications and devices. This will also take more funding as well as redirection of efforts. Increased security of our devices and simultaneous increased capabilities of law enforcement are the only sensible approach to a world where securing the bits, whether of health data, financial information, or private emails, has become of paramount importance.

Or: The FBI needs computer-security expertise, not backdoors.

Patrick Ball writes about the dangers of backdoors.

EDITED TO ADD (9/23): Good article from the Economist.

Posted on September 15, 2016 at 8:54 AM • 45 Comments