Optimizing Picnic for Limited Memory Resources

Picnic is a post-quantum digital signature scheme, where the security is based on the difficulty of inverting a symmetric block cipher and zero-knowledge proofs. However, generating a Picnic signature to a specific message requires up to 300 kB content depending RAM. As the memory of an IoT device is limited this can lead to issues at the implementation. Our target is bringing post-quantum cryptography to IoT systems. We propose three structural adjustments of the Picnic algorithm to reduce the memory usage. Two adjustments are compatible with the reference implementation, one of them breaks backward compatibility. We show analytically that the content depending memory for generating a signature can be decreased to under 10 kB.With these adjustments, Picnic becomes suitable for IoT devices with little RAM. Since our approach also aims at easier parallelization, a speed-up depending on the number of instances is possible.