Reaction Attack on CKKS Deployments with Asymptotically Optimal Query Complexity
The study shows that combining public coefficient-to-slot keys with a client's 1-bit validity response allows an attacker to recover ternary secret keys in asymptotically optimal query complexity. This attack exploits the interaction between validity checks and public homomorphic transformations, proving that observable reactions can leak secret information without breaking the underlying RLWE security.