Computer Laboratory

Course pages 2011–12

Security I

Principal lecturer: Dr Markus Kuhn
Taken by: Part IB
Past exam questions: Security I, Introduction to Security
Information for supervisors (contact lecturer for access permission)

No. of lectures: 12
Prerequisite courses: Discrete Mathematics II, Operating Systems
This course is a prerequisite for Security II.


This course covers essential concepts of computer security and cryptography.


  • Cryptography. Introduction, terminology, finite rings and fields, modular arithmetic, GF($2^n$), pseudo-random functions and permutations.

  • Classic ciphers. Vigenére, perfect secrecy, Vernam, computational security, Kerckhoffs’ principle, random bit sources.

  • Stream ciphers. Attacking linear-congruential RNGs and LFSRs, Trivium, RC4.

  • Block ciphers. SP networks, Feistel/Luby-Rackoff structure, DES, AES, modes of operation, message authentication codes.

  • Secure hash functions. One-way functions, collision resistance, Merkle-Damgård construction, padding, birthday problem, MD5, SHA, HMAC, stream authentication, Merkle tree, Lamport one-time signatures.

  • Asymmetric cryptography. Key-management problem, signatures, certificates, PKI, discrete-logarithm problem, Diffie-Hellman key exchange, ElGamal encryption and signature, hybrid cryptography.

  • Entity authentication. Passwords, trusted path, phishing, CAPTCHA. Authentication protocols: one-way and challenge-response protocols, Needham-Schroeder, protocol failure examples, hardware tokens.

  • Access control. Discretionary access control matrix, DAC in POSIX and Windows, elevated rights and setuid bits, capabilities, mandatory access control, covert channels, Clark-Wilson integrity.

  • Operating system security. Trusted computing base, domain separation, reference mediation, residual information protection.

  • Software security. Malicious software, viruses. Common implementation vulnerabilities: buffer overflows, integer overflows, meta characters, syntax incompatibilities, race conditions, unchecked values, side channels.

  • Network security. Vulnerabilities of TCP/IP, DNS. HTTP authentication, cookies, cross-site scripting, browser sandboxes. Firewalls, VPNs.

  • Security policies and management. Application-specific security requirements, targets and policies, security management, BS 7799.


By the end of the course students should

  • be familiar with core security terms and concepts;

  • have a basic understanding of some commonly used attack techniques and protection mechanisms;

  • have gained basic insight into aspects of modern cryptography and its applications;

  • appreciate the range of meanings that “security” has across different applications.

Recommended reading

* Paar, Ch. & Pelzl, J. (2010). Understanding cryptography. Springer.
Gollmann, D. (2010). Computer security. Wiley (3rd ed.).