Very compact (or tweetable) implementations of Keccak, written by D. J. Bernstein, Peter Schwabe and Gilles, are now available. In their most compact form, the 6 instances of SHA-3 and SHAKE can fit in just 9 tweets.

We published a series of compact implementations, from the more readable one to the most compact one.

• First, a readable and compact implementation of all the Keccak instances approved in the FIPS 202 standard, where we focused on clarity and on source-code compactness (excluding the comments), rather than on the performance. As much as possible, we used the same notation as in the specifications.
• Second, a more compact (but less readable) implementation, demonstrating that Keccak is conceptually simple.
• Third, a very compact implementation aimed at minimizing the number of tweets (i.e., lines of up to 140 characters each). With just 9 tweets, this means an average of 1.5 tweets per instance! As a comparison, SHA-512 alone takes about 27 tweets when extracted from TweetNaCl.

Dan presented the tweetable implementation at the rump session of Crypto 2015 [slides].