by the way,

today's paper was great. i feel like i'm Da Vinci. (: finding a substitution cipher to encrypt and decrypt messages. this is so cool. let's try it out.

first, let me explain wad is a substitution cipher - every occurrence of a given letter is replaced systematically by another letter.

eg. using sub cipher of "letter plus two", decrypt HELLO. ans: JGNNQ

SO, the question is like that.

QUESTION: Find a sub cipher such that you can use exactly the SAME cipher to encrypt and decrypt messages. In other words,

Message: "I love you" ---apply cipher----> ciphered text


ciphered text ----apply same cipher------->Message: "I love you"

demonstrate the cipher on the message. (:

OKAYS, maybe its easy lar, if so, then i am stupid. CUZ i really spent quite some time thinking of this. AND AND AND! while i was doing, i kept laughing to myself cuz i really feel like da vinci. HAHAHA. and prof tan saw me laughing. DAMN. (: