I am interested in fixed pseudo-random permutation algorithms that are defined for any number of words in the input (but there might be some minimal number of words, e.g. 8), where the word size may be 8/16/32/64 bits. Such permutation may be used as the core function in sponge construction for hashing the message.

The only example that I have found is MD6 core function (although it may be slow, and I don't know if it can be used as a basis of the sponge construction).

Are there any newer (maybe experimental, with unknown cryptographical security) algorithms that match the above requirements?

  • $\begingroup$ ‘Fixed pseudo-random permutation’ is a contradiction in terms. Are you asking about a fixed permutation, or are you asking about a keyed pseudorandom permutations family? If you're asking for a fixed permutation—or a fixed permutation ensemble, indexed by the size—you're unlikely to get an answer because general cryptographic practice is to start with a fixed-size primitive and then use a generic domain extender to extend it to variable sizes. $\endgroup$ – Squeamish Ossifrage Apr 23 '19 at 15:23
  • $\begingroup$ There are some systems with variable-width blocks like XXTEA and the Hasty Pudding Cipher but they are broken and the design never caught on. How you conclude that the MD6 core function is defined for any number of words in the input is unclear—the specification clearly defines it on exactly 89 words (of which 15 are constant, much like Salsa20). $\endgroup$ – Squeamish Ossifrage Apr 23 '19 at 15:26

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