Security

Lecturer: Dr R. Anderson (rja14@cl.cam.ac.uk)

No. of lectures: 12

Prerequisite courses: Introduction to Security, Discrete Mathematics, Operating Systems, Digital Communication I, Digital Communication II, Information Theory and Coding

Aims

This course aims to give students a thorough understanding of computer security technology. This includes high-level issues such as security policy (modelling what ought to be protected) and engineering (how we can obtain assurance that the protection provided is adequate). It also involves the protection mechanisms supported by modern processors and operating systems; cryptography and its underlying mathematics; electrical engineering issues such as tempest and tamper resistance; and a wide variety of attacks ranging from network exploits through malicious code to protocol failure.

Lectures

• What is security? A review of security applications and policy models. Bell-LaPadula, the lattice model, Clark-Wilson, Biba, Chinese Wall, the BMA policy.

• Introduction to access control. Access matrices, access control lists, capabilities, role-based systems, granularity. VME and MVS systems; Intel processors. Typical vulnerabilities: social engineering, password cracking.

• Unix and Internet security. The Internet worm. Attacks based on the TCP/IP protocol suite and on stack overflow. Firewalls. Intrusion detection and audit.

• Malicious code and countermeasures. Trojans: the motivation for multilevel security. The problems: polyinstantiation and covert channels. Composability of trusted systems. Viruses: scanners, checksummers and their vulnerabilities. Defensive techniques inspired by biology.

• Information hiding. Steganography. Covert channels. Subliminal channels. Copyright marking schemes. Tempest.

• Stream ciphers. Historical systems: Caesar, Vigenère, Playfair. The role of information theory: unicity distance and the one-time-pad. Shift register based systems: the multiplexer generator, the filter generator, A5. Attacks on these systems: divide and conquer, fast correlation.

• Block ciphers. Typical block ciphers: SAFER, TEA, DES. The theory of block ciphers: differential and linear cryptanalysis, the random oracle model. Splicing and meet-in-the-middle attacks. Message authentication codes and hash functions.

• Symmetric cryptographic protocols. Needham-Schroder, Otway-Rees, Kerberos, the wide-mouthed frog. The BAN logic.

• Asymmetric cryptosystems. Euler's theorem and RSA: an overview of factoring algorithms. Schemes based on discrete logarithm. Identity based and threshold schemes; zero knowledge; blind signatures and digital cash.

• Asymmetric cryptographic protocols. Needham-Schroder, Denning-Sacco, TMN. Applications including SSL, SSH, SET, PGP and PEM. The BAN logic applied to public key systems.

• Security engineering. What goes wrong with real systems. Examples from banking, military and other applications. Threat trees; risk models; robustness; dependability; engineering disciplines. Verification and evaluation: TCSEC, ITSEC and the Common Criteria.

• Legal and organisational aspects of computer security. Why is security management hard? Risk reduction versus transference, due diligence and the role of insurance. The Data Protection Act; the Computer Misuse Act; international aspects. Export control and key escrow.

Objectives

At the end of the course students should be able to tackle an information protection problem by drawing up a threat model, formulating a security policy, and designing specific protection mechanisms to implement the policy.

Recommended books

Gollmann, D. (1999). Computer Security. Wiley.
Schneier, B. (1995). Applied Cryptography: Protocols, Algorithms, and Source in C. Wiley (2nd ed.).

Further reading:

Kahn, D. (1966). The Codebreakers: the Story of Secret Writing. Weidenfeld and Nicolson.
Cheswick, W.R. & Bellovin, S.M. (1994). Firewalls and Internet Security: Repelling the Wily Hacker. Addison-Wesley.
Biham, E. & Shamir, A. (1993). Differential Cryptanalysis of the Data Encryption Standard. Springer-Verlag.
Koblitz, N. (1994). A Course in Number Theory and Cryptography. Springer-Verlag (2nd ed.).
Neumann, P. (1994). Computer Related Risks. Addison-Wesley.
Leveson, N.G. (1995). Safeware: System Safety and Computers. Addison-Wesley.
Garfinkel, S. & Spafford, G. (1996). Practical Unix and Internet Security. O'Reilly (2nd ed.).
Davies, D.W. & Price, W.L. (1984). Security for Computer Networks. Wiley.
Beker, H. & Piper, F. (1982). Cipher Systems. Northwood.
Cohen, F.B. (1994). A Short Course on Computer Viruses. Wiley (2nd ed.).
Amoroso, E. (1994). Fundamentals of Computer Security Technology. Prentice-Hall.