Cryptology

Cryptology

1. Cryptography

   • The science of writing secret codes to hide the meaning of the message
   • Symmetric Ciphers
     • Two parties haven an encryption and decryption method for which they share a secret key
     • Ancient times - 1976
     • Still used today for data encryption and integrity check of messages
     • i.e. substitution cipher
       • attack #1 = exhaustive key search
       • attack #2 = letter frequency analysis
   • Asymmetric Ciphers
     • Also called Public-Key
   • Protocols
     • hash functions

2. Cryptanalysis

   • The science and art of breaking cryptosystems 
   • Only way to know that a cryptosystem is secure
   • Classic cryptanalysis
   • Attacks
     • Implementation attacks
     • Social engineering attacks
       • KERCKHOFFS' PRINCIPLE
         • A cryptosystem should be secure even if the attacker knows all details about the system, with the exception of the secret key. In particular, the system should be secure when the attacker knows the encryption and decryption algorithms
         • Security by obscurity
         • A cryptosystem should be secure even if everything about the system, except the key, is public knowledge
     • analytical & brute force
   • Lengths of ciphers
     • Short-term
     • Medium-term
     • Long-term

3. Cipher

   • Algorithm for performing encryption and decryption