Cryptography

a. Assume that a=15 and b=12 in affine cipher. What is the encryption of 8,11 , and 13 (e(8), e(11),e(13)) ? What is the decryption of 8,11 , and 13(d(8),d(11),d(13)) ? b. An obvious approach to increase the security of a symmetric algorithm is to apply the same cipher twice, i.e.: y=ek2(ek1(x)) As is often the case in cryptography, things are very tricky and results are often different from the expected and/ or desired ones. In this problem we show that a double encryption with the affine cipher is only as secure as single encryption! Assume two affine ciphers ek1=a1x+b1 and ek2=a2x+b2. Show that there is a single affine cipher ek3=a3x+b3 which performs exactly the same encryption (and decryption) as the combination ek2(ek1(x) ). Find the values for a3,b3 when a1=11,b1=8 and a2=17,b2=12