Caesar Cipher

Shift every letter by a fixed amount. One number is the whole key, and the whole keyspace fits on one screen.

Monoalphabeticdemo

Objectives

33%

C = (P + k) mod 26; D = (C − k) mod 26; key = one number, 1–25.

Plaintext

Shift k

plain

cipher

ciphertext

ZHKDY HDPRO HDERU WWKHG HDO

Keyspace: 25. Twenty-five is small enough that you do not need to find the weakness in the cipher at all; you can try them all.

Brute force needs you to recognise the right answer. You can do that for 25 candidates. For 26! you need a statistic instead.

step 1/3