# 16-bit entry in a S-Box of a SPN block cipher: Would it have the same speed/performance than a 8-bit entry?

I learned that in Substitution–permutation block ciphers, the maximum size of S-Box set to receive an entry from a data is the max numeric count of the data, for example, if the entry is 8-bits the S-Box set to be used is 256-bytes as 2^8=256.

Would 16-bits entries in a S-Box set of 65536-bytes (2^16) deliver the same speed/performance (cycles per byte) to the cipher as well as if was used 8-bits entries in a 256-byte S-Box set?

16-bits entries require a larger S-Box set (65536 bytes), would it be 256 times slower that if it was used a 8-bits entry? (as 65536/256=256).

• Speed is generally dependent on implementation details. Apr 6, 2022 at 9:12

Firstly note that a $$2^{16}$$-long look up table of 16-bit=2-byte entries takes up 131,072 bytes of space.