This is the public reference implementation of an anonymous block cipher called S-1: https://en.wikipedia.org/wiki/S-1_block_cipher

This code was taken from: https://groups.google.com/g/sci.crypt/c/vLtuBDoqPfc/m/jm6MshFbomgJ

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See also:
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The S-1 Algorithm: https://groups.google.com/g/sci.crypt/c/l4nsjVu27lU/m/LIycdmVxJZ0J
Cryptanalysis of S-1: https://groups.google.com/g/sci.crypt.research/c/5N0zarU4XPs

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PS: I don't know the key and block sizes that this cipher uses and neither the number of rounds that should be used with different key/block sizes.