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Introduction to Information Security

Introduction to Information Security. Pieter.Hartel@utwente.nl. Overview. Definitions Design issues Cryptography Security Protocols.

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Introduction to Information Security

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  1. Introduction toInformation Security Pieter.Hartel@utwente.nl

  2. Overview • Definitions • Design issues • Cryptography • Security Protocols [And08] R. J. Anderson. Security Engineering: A guide to building dependable distributed systems. John Wiley & Sons Inc, New York, Second edition, 2008. http://www.cl.cam.ac.uk/~rja14/book.html [Sch04b] B. Schneier. Secrets and Lies: Digital Security in a Networked World. Wiley Publishing Inc, Indianapolis, Indiana, second edition, 2004. http://www.schneier.com/book-sandl.html 2 IIS

  3. Definitions [Men01a] A. J. Menezes, P. C. van Oorschot, and S. A. Vanstone. Chapter 1 of Handbook of applied cryptography. CRC Press, 2001. http://www.cacr.math.uwaterloo.ca/hac/

  4. Security is asset protection owners1 wish to minimize to reduce countermeasures5 impose that may be reduced by value that may possess vulnerabilities4 may be aware of threat agents7 that exploit leading to to risk3 give rise to that increase threats6 to assets2 wish to abuse and/or may damage [ISO09] ITSEC. Information technology security techniques evaluation criteria for IT security part 1: Introduction and general model. Int. Standard ISO/IEC 15408-1, ISO/IEC, Dec 2009. http://standards.iso.org/ittf/PubliclyAvailableStandards/c050341_ISO_IEC_15408-1_2009.zip 4 IIS

  5. Definitions • Availability: authorised users want the system to work as/when they expect it to • Reliability: the ability of a system or component to perform its required functions • Safety: being protected against non-desirable events (not specifically malicious) • Confidentiality: to stop unauthorised users from reading sensitive information • Integrity: Every data item/system component is as the last authorised modifier left it • Maintainability: ease with which a software product can be modified 5 IIS

  6. Dependability vs. Security Dependability Security [Avi04] A. Avižienis, J.-C. Laprie, B. Randell, and C. Landwehr. Basic concepts and taxonomy of dependable and secure computing. IEEE Trans. on Dependable and Secure Computing, 1(1):11-33, Jan 2004. http://doi.ieeecomputersociety.org/10.1109/TDSC.2004.2 6 IIS

  7. Access control model – AU3 Authentication Authorisation Do Operation Principal Reference Monitor Object Source request guard resource Audit log • Authentication: determine who makes request • Authorisation: determine who is trusted to do which operation on an object • Auditing: determine what happened and why [Lam04] B. W. Lampson. Computer security in the real world. IEEE Computer, 37(6):37-46, Jun 2004. http://doi.ieeecomputersociety.org/10.1109/MC.2004.17 7 IIS

  8. Privacy vs. Security • Privacy is the right of an individual to determine what information about oneself to share with others • Security can help • Selectively encrypt data • Security can hinder • Calling home to prevent piracy • (Audit) logging [War1890] S. D. Warren and L. D. Brandeis. The right to privacy. Harvard Law Review, 4(5):193-220, Dec 1890. http://www.jstor.org/stable/1321160 8 IIS

  9. Design issues

  10. Good: As secure as the real world [Lam04] Defense in depth Make it usable Be explicit about: naming, typing, freshness, assumptions, goals, limitations etc [And95a] Bad: Design security as an afterthought Security by obscurity [Ker1883] Make it complicated Examples of design goals [Ker1883] A. Kerckhoffs. La cryptographie militaire. J. des Sciences Militaires, IX:5-38, Jan 1883. http://www.petitcolas.net/fabien/kerckhoffs/ 10 IIS

  11. Tools • Policy – what is supposed to happen? • Access control • Mechanisms – how should it happen? • Tamper resistance • Biometrics • Cryptography, Hashing, Random numbers • Assurance – does it work? • Risk management • Protocol verification 11 IIS

  12. Attacks • Definition: a successful exploitation of a vulnerability • Examples: • Attacker shuts you out by trying to log in as you • Cold boot attack (remember the movie?) [Hal08] J. A. Halderman, S. D. Schoen, N. Heninger, W. Clarkson, W. Paul, J. A. Calandrino, A. J. Feldman, J. Appelbaum, and E. W. Felten. Lest we remember: Cold boot attacks on encryption keys. In 17th USENIX Security Symp., pp 45-60, San Jose, California, Jul 2008. USENIX Association. http://citp.princeton.edu/memory/ 12 IIS

  13. Cryptography [Men01a] A. J. Menezes, P. C. van Oorschot, and S. A. Vanstone. Chapter 1 of Handbook of applied cryptography. CRC Press, 2001. http://www.cacr.math.uwaterloo.ca/hac/

  14. “gfd6#Q” “attack” Algorithms + keys • Cipher (aka cryptosystem) • “Public” algorithm + • Secret keys “attack” “sdwr$350” encrypt decrypt 14 IIS

  15. Symmetric ciphers • Public algorithm + one secret key • Standard algorithms: DES, AES • Example: one time pad 15 IIS

  16. Asymmetric ciphers • Public algorithm+private key+public key • Example: El Gamal • Multiplicative group Zn*={1...n-1} with n prime • Generator g: Zn* = { gi | i  N } • Private key: x  Zn* • Public key: h = gx • Salt: y R Zn* • Enc(m,h): (c,d) = (mhy,gy) • Dec((c,d),x): c/dx • Exercise: prove that this works... All calculations modulo n 16 IIS

  17. Random numbers • Pseudo random in SW • True random in HW • Standard statistical tests • NIST web site • For example • Linear Congruential Method • r0 = s • rn+1=(a rn+c) mod m • Cyclic  • Deterministic  17 IIS

  18. Hash functions • Map arbitrary bit string to fixed size output • Easy to calculate for given input • Practically impossible to invert • Extremely unlikely that two inputs give the same hash • For example • Knuth’s variant on Division • Hash(n) = n(n+h) mod m • Try it out… 18 IIS

  19. Visual Cryptography [Nao97] M. Naor and B. Pinkas. Visual authentication and identification. In Burton S. Kaliski Jr., editor, 17th Int. Conf. on Advances in Cryptology (CRYPTO), volume LNCS 1294, pages 322-336, Santa Barbara, California, Aug 1997. Springer. http://www.springerlink.com/content/ghv31wm0pexkd3kq/ 19 IIS

  20. Security Protocols [And95a] R. J. Anderson and R. Needham. Programming satan's computer. In J. van Leeuwen, editor, Computer Science Today, volume LNCS 1000, pages 426-440. Springer, 1995. http://dx.doi.org/10.1007/BFb0015258

  21. Definitions • Sequence of communications by two or more parties to achieve security objective(s) • Not like this (why?): 21 IIS

  22. Dolev Yao attacker model • Eve can: • See all messages • Delete, alter, inject and redirect messages • Initiate new communications • Reuse messages from past sessions • Eve cannot: • Solve “hard” problems (such as?) • Guess pseudo-random values (eg. nonces) • Get another identity (identity theft) • Time computations • What to do: Make everything explicit 22 IIS

  23. Design is hard • ‘‘Security protocols are three line programs that people still manage to get wrong’’ (Roger Needham) [Low96] G. Lowe. Breaking and fixing the Needham-Schroeder Public-Key protocol using FDR. In 2nd Int. Workshop on Tools and Algorithms for the Construction and Analysis of Systems (TACAS), volume LNCS 1055, pages 147-166, Passau, Germany, Mar 1996. Springer. http://dx.doi.org/10.1007/3-540-61042-1_43 23 IIS

  24. Authentication protocol (1) • What’s the problem with this? • The nonce Nb leaks, so it cannot be used to secure the session 24 IIS

  25. Authentication protocol (2) • (Wo)man in the middle attack: 25 IIS

  26. Authentication protocol (3) • Does it work now? 26 IIS

  27. Conclusions • Consider the system as a whole • Know your enemy • Be explicit • Use standard tools 27 IIS

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