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Asked: 2026-06-14T12:05:17+00:00

I’m taking a crypto course, and we’re going over substitution ciphers and their Key

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I’m taking a crypto course, and we’re going over substitution ciphers and their Key space.
per the instructor, the key space is 26! (approx 2^88) for the English alphabet. there is no reference to key length, probably because a subst cipher’s length would be a function of the length of the alphabet, just as the number of options would.

per wikipedia the keyspace is the set of all possible keys of a certian length, and is calculated in the same way brute force try counts would be options^length or in this case 26^26.

so what am I not getting here?

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1 Answer

  1. Editorial Team

    If your key is a set of digits, options^length is correct. Every digit may occur several times.

    If your key is an alphabet, Factorial N is correct. Say, you want to place the A first. You have 26 options. After that, you have only 25 options for the B because A already occupies one. 24 For the C and so on.

    26*25*24*…*1 = 26!

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