Think about how to decrypt the Affine Cipher

Decryption

Inverse’of’multiplicative’cipher

How to compute the inverse of a key (Trial and Error Approach

Exercise

Decryption

Computational effort to break Affine Cipher

$$12 * 26 = 312$$

• Brute-force 312 keys.

Cryptoanalysis o Affine Cipher

• The Affine cipher incresed the key space over shift cipher

• However, it is still susceptible to:

  • Brute-Force and Frequency analysis attacks

Ciphertext: $y = {VKZIBEVCCH}$