Unpatchable Vulnerability in Apple Chip Leaks Secret Encryption Keys
Freeman writes:
A newly discovered vulnerability baked into Apple's M-series of chips allows attackers to extract secret keys from Macs when they perform widely used cryptographic operations, academic researchers have revealed in a paper published Thursday.
The flaw-a side channel allowing end-to-end key extractions when Apple chips run implementations of widely used cryptographic protocols-can't be patched directly because it stems from the microarchitectural design of the silicon itself.
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cryptographic engineers have devised constant-time programming, an approach that ensures that all operations take the same amount of time to complete, regardless of their operands. It does this by keeping code free of secret-dependent memory accesses or structures.The breakthrough of the new research is that it exposes a previously overlooked behavior of DMPs in Apple silicon: Sometimes they confuse memory content, such as key material, with the pointer value that is used to load other data. As a result, the DMP often reads the data and attempts to treat it as an address to perform memory access. This "dereferencing" of "pointers"-meaning the reading of data and leaking it through a side channel-is a flagrant violation of the constant-time paradigm.
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The attack, which the researchers have named GoFetch, uses an application that doesn't require root access, only the same user privileges needed by most third-party applications installed on a macOS system.
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The GoFetch app connects to the targeted app and feeds it inputs that it signs or decrypts. As its doing this, it extracts the app secret key that it uses to perform these cryptographic operations. This mechanism means the targeted app need not perform any cryptographic operations on its own during the collection period.
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The DMP on the M3, Apple's latest chip, has a special bit that developers can invoke to disable the feature. The researchers don't yet know what kind of penalty will occur when this performance optimization is turned off. (The researchers noted that the DMP found in Intel's Raptor Lake processors doesn't leak the same sorts of cryptographic secrets. What's more, setting a special DOIT bit also effectively turns off the DMP.)
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