International Association
for Cryptologic Research

We present the first side-channel attack on a lattice-based signature scheme, using the FLUSH+RELOAD cache-attack. The attack is targeted at the discrete Gaussian sampler, an important step in the Bimodal Lattice Signature Schemes (BLISS). After observing only 450 signatures with a perfect side-channel, an attacker is able to extract the secret BLISS-key in less than 2 minutes, with a success probability of 0.96. Similar results are achieved in a proof-of-concept implementation using the FLUSH+RELOAD technique with less than 3500 signatures.

We show how to attack sampling from a discrete Gaussian using CDT or rejection sampling by showing potential information leakage via cache memory. For both sampling methods, a strategy is given to use this additional information, finalize the attack and extract the secret key.

We provide experimental evidence for the idealized perfect side-channel attacks and the FLUSH+RELOAD attack on two recent CPUs.