Dr. Jaffe
Advanced Topics in Mathematics
Homework due 12/16
NAME: ____________________________________________________________
1. If the most common letter in a long ciphertext, enciphered by a shift transformation C ≡ P + k (mod 26) is Q, then
what is the most likely value of k?
2. If the two most common letters in a long ciphertext, enciphered by an affine transformation C ≡ aP + b (mod 26)
are W and B, respectively, then what are the most likely values of a and b?
3. Encrypt the message THE RIGHT CHOICE using the affine transformation C ≡ 15P + 14 (mod 26).
4. CHALLENGE PROBLEM:
Given two ciphers, plaintext may be enciphered by using one of the ciphers, and by then using the other cipher.
This procedure produces a product cipher.
Find the product cipher by using the transformation C ≡ 5P + 13 (mod 26) followed by the transformation
C ≡ 17P + 3 (mod 26)