Extracting Qualcomm’s KeyMaster Keys – Breaking Android Full Disk Encryption

Even with full-disk encryption, Qualcomm-based Android devices can be broken by OEMs who can self-sign TrustZone images to extract master keys which can then be brute-forced. Thus, set a sufficiently strong MASTER encryption password (the one that only needs to be entered on boot), preferably at least 16-20 characters with good entropy. To my knowledge, non-rooted devices CANNOT set a separate boot and unlock password, which is a huge inconvenience and usually ends up sacrificing security. Rooted users can set a strong password for boot, and a 4-digit or pattern code for normal unlock use. It’s important to note, this is not a flaw in dm-crypt (which has been used in Linux for eons), but in Qualcomm’s implementation of FDE.

“Full disk encryption is used world-wide, and can sometimes be instrumental to ensuring the privacy of people’s most intimate pieces of information. As such, I believe the encryption scheme should be designed to be as “bullet-proof” as possible, against all types of adversaries. As we’ve seen, the current encryption scheme is far from bullet-proof, and can be hacked by an adversary or even broken by the OEMs themselves (if they are coerced to comply with law enforcement).”

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