Paper 2022/952

When Frodo Flips: End-to-End Key Recovery on FrodoKEM via Rowhammer

Abstract

In this work, we recover the private key material of the FrodoKEM key exchange mechanism as submitted to the NIST Post Quantum Cryptography (PQC) standardization process. The new mechanism that allows for this is a Rowhammer-assisted \emph{poisoning} of the FrodoKEM Key Generation (KeyGen) process. The Rowhammer side-channel is a hardware-based security exploit that allows flipping bits in DRAM by “hammering” rows of memory adjacent to some target-victim memory location by repeated memory accesses. Using Rowhammer, we induce the FrodoKEM software to output a higher-error Public Key (PK), $(\mathbf{A}, \mathbf{B} = \mathbf{A}\mathbf{S}+\mathbf{\widetilde{E}}),$ where the error $\widetilde{\mathbf{E}}$ is modified by Rowhammer. Then, we perform a decryption failure attack, using a variety of publicly-accessible supercomputing resources running on the order of only 200,000 core-hours. We delicately attenuate the decryption failure rate to ensure that the adversary's attack succeeds practically, but so honest users cannot easily detect the manipulation. Achieving this public key "poisoning" requires an extreme engineering effort, as FrodoKEM's KeyGen runs on the order of 8 milliseconds. (Prior Rowhammer-assisted attacks against cryptography require as long as 8 hours of persistent access.) In order to handle this real-world timing condition, we require a wide variety of prior and brand new, low-level engineering techniques, including e.g. memory massaging algorithms -- i.e. "Feng Shui" -- and a precisely-targeted performance degradation attack on the extendable output function SHAKE. We explore the applicability of our techniques to other lattice-based KEMs in the NIST PQC Round 3 candidate-pool, e.g. Kyber, Saber, etc, as well as the difficulties that arise in the various settings. To conclude, we discuss various simple countermeasures to protect implementations against this, and similar, attacks.