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If I wrote RC5-32/12/16, it would mean 32-bit words (which is 64-bit data blocks). What is "words".

I know the 12 is rounds and 16 is key size (16 bytes, so 128 bit).

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up vote 8 down vote accepted

The word size can be 16, 32, or 64 bits, and it determines the block size. "The algorithm assumes that the input block is given in two w-bit registers A and B..." This allows for optimization based on the target architecture.

Reference: The RC5 Encryption Algorithm (PDF)

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