1. The problem statement, all variables and given/known data "Compare this cipher (transposition cipher) to a mixed (substitution) cipher and state under what circumstances a transposition cipher can be thought of as a mixed cipher." 2. Relevant equations --- 3. The attempt at a solution For the first part of a question I stated that a mixed/substitution cipher changes the letters of the plaintext but not the order whilst a transposition cipher changes the order but not the letters of the plaintext (thus can be analysed through letter frequency count). For the second part the only example I can think of is the obvious cipher where nothing changes, but I'm pretty sure that's not what they're looking for. Any clues? EDIT: I tried taking a general example and got that they were only equivalent when the shift was zero and every letter was equal. I think I'm on the totally wrong track here. :/ Thanks!