A (Bit)slice of Rainbow.

We explore the performance impact of bitslicing on implementations of the NIST PQC Round 3 Finalist Digital Signature Algorithms: Rainbow. We show that for the Ia parameters set, when not using special or vector instructions, our bitsliced implementation signs 40% faster and verifies 50% faster than the submission implementation while remaining constant time. We argue that using this technique, when combined with vector instructions might lead to substantial speed-up as well.