Cryptography

Forms of attack:
ciphertext-only
known-plaintext
chosen-plaintext

Forms of Cryptosystems

Private Key:
A single key is used for both encryption and decryption.
Key distribution problem - a secure channel is needed to transmit the key before secure communication can take place over an unsecure channel.
Public Key:
The encryption procedure (key) is public while the decryption procedure (key) is private.
Requirements:
  1. For every message M, D(E(M)) = M
  2. E and D can be efficiently applied to M
  3. It is impractical to derive D from E.
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