ceasar cipher uses a shift to move the letters along by the same ammount. Hi and a shift of 4 would LM vernam cipher uses a key generated that is as long as the text you want to Encrypt. then you XOR each character value togerther that you have decided on, to get a Bitwise XOR result. Computational security is when it may be posable to crack the enctyption but its very inporactical to do whereas Perfect security means thats it is inposable to crack. there is nothing in the string that can help you to crack the code