Data Encryption Standard

• Most widely used encryption standard by banks

• Predates more famous “public key” cryptography

• DES encodes blocks of 64 bits at a time

• Key is length 56 bits

• Loop 16 times

  • break the plaintext in 2
  • combine one half with the key using “clever function” f
  • XOR combination with the other half
  • swap the two parts

• Security depends on the 16 iterations and on f