Differential Attacks on Deterministic Signatures.

Deterministic signature schemes are becoming more popular, as illustrated by the deterministic variant of ECDSA and the popular EdDSA scheme, since eliminating the need for high-quality randomness might have some advantages in certain use-cases. In this paper we outline a range of differential fault attacks and a differential power analysis attack against such deterministic schemes. This shows, contrary to some earlier works, that such signature schemes are not naturally protected against such advanced attacks. We discuss different countermeasures and propose to include entropy for low-cost protection against these attacks in scenarios where these attack vectors are a real threat: this does not require to change the key generation or the verification methods and results in a signature scheme which offers high performance and security for a wide range of use-cases.