Classical cryptography, substitution ciphers, permutation (transposition) cipher, symmetric cryptography, stream ciphers (RC4, A5/1), block ciphers(DES, 3DES). Asymmetric cryptography, Diffie-Hellman key exchange, certificates, basics of public key infrastructure (PKI). Authentication (passwords, biometrics), authorization (Access control lists, capabilities), multi-level security, security modeling, firewalls, CAPTCHA?s, intrusion detection systems, software flaws, buffer overflow, viruses, worms, trojan horses, and other forms of malicious code.