Did a C++ code on Caesar Cipher to do encryption and decryption with my XMC4500 microcontroller but my lecturer said that Caesar Cipher is too simple. He wants me to use a non basic type of cipher and to include size of bit length of plain text and cipher text, secret and public message number and key. And the problem is no keyboard or display interface will be connected to my microcontroller so i could not use printf, scanf, cout and cin to input any of those values. Any ideas on what Cipher I should use and how I could do it?
UPDATE: Thank you for all the suggestions but my supervisor finally told me to use ASCON instead.