In October 2012 NIST announced that the SHA-3 hash standard will be based on Keccak. Besides hashing, Keccak can be used in many other modes, including ones operating on a secret value. Many applications of such modes require protection against sidechannel attacks, preferably at low cost. In this paper, we present threshold implementations (TI) of Keccak with three and four shares that build further on unprotected parallel and serial architectures. We improve upon earlier TI implementations of

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... eccak in the sense that the latter did not achieve uniformity of shares. In our proposals we do achieve uniformity at the cost of an extra share in a four-share version or at the cost of injecting a small number of fresh random bits for each computed round. The proposed implementations are efficient and provably secure against first-order side-channel attacks.