For improved attack on shift cipher we can associate letters of English alphabet with numbers 0...25. Let pi denote the probability of the i-th letter in English text Using the frequency table: 2250P; 2 0.065 Let qi denote the probability of the i-th letter in this ciphertext: # of occurrences/length of ciphertext Compute 1; = = Pi . qi+j for each possible shift value j Output the value k for which Ik is closest to 0.065. 1; by Loli+j What happens if replace Will the attack work? For improved attack on shift cipher we can associate letters of English alphabet with numbers 0...25. Let pi denote the probability of the i-th letter in English text Using the frequency table: 2250P; 2 0.065 Let qi denote the probability of the i-th letter in this ciphertext: # of occurrences/length of ciphertext Compute 1; = = Pi . qi+j for each possible shift value j Output the value k for which Ik is closest to 0.065. 1; by Loli+j What happens if replace Will the attack work