1. Class 2 Cryptography Refresher CIS 755: Advanced Computer Security Spring 2014 Eugene Vasserman http://www.cis.ksu.edu/~eyv/CIS755_S14/

2. Administrative stuff Room change: Nichols 236 Office hours: – Monday 2 – 3:30 PM – Friday 2:30 – 4 PM – Or by appointment – In 316A Nichols Watch for quiz announcements Be sure to do the reading!! How was the reading?

3. Final projects (50% of your grade) (20%) Proposal (with projected timeline) (15%) Progress report (20%) Final presentation (in class) (45%) Final report (100% total for final project) Due dates will be posted in the schedule

4. Me being selfish Any questions about my research? (Just what is it that I do around here? :)

5. Security basics “What is being secured?” – And security goal/property “Secure against what?” – Threat/attacker model, players and resources Kerckhoffs’ principle – Roughly, the only thing secret about a security system should be the secret key Shannon’s maxim – “The enemy knows the system”

6. Always state your assumptions!

7. More basics Trusted vs. trustworthy – e.g. the recent SSL Certificate Authority fiasco Risk, hazard, vulnerability – Adversary, ROI, scale Assurance levels – “Rainbow” book series, Common Criteria Method of returning to secure states Fail-closed/secure or fail-open/insecure?

8. Attack success variants Derive/recover secret key – Total break Forge signature/tag on any message – Universal break Forge for some chosen messages – Selective break Forge for some (garbled?) message – Existential break xkcd.com

9. Basic cryptographic primitives Confidentiality (encryption) – Symmetric (e.g. AES) – Asymmetric (e.g. RSA) Hash functions Integrity and authentication – Symmetric (authentication codes) – Asymmetric (signatures) Key agreement Random numbers

10. Encryption Basic idea: someone seeing ciphertext learns nothing about plaintext without correct key With or without authentication Symmetric – based on tests/best guess – e.g. AES (block cipher) Asymmetric – based on math assumptions – e.g. RSA

11. Security properties of encryption Semantic security Chosen plaintext security (IND-CPA) Chosen ciphertext security (IND-CCA) – IND-CCA2 Security proof “games”

12. Aside: Information theory Conditional vs. unconditional security – Unconditional, e.g. one-time pad – Conditional e.g. RSA, AES … Symmetric encryption Hash functions Remember: confusion and diffusion

13. Basic (but more complex) primitives Confidentiality (encryption) – Symmetric (e.g. AES), asymmetric (e.g. RSA) – Malleable vs. non-malleable – Deterministic vs. randomized Hash functions Message authentication codes, signatures Random numbers Key agreement

14. Some basic cryptographic primitives Confidentiality (encryption) – Symmetric (e.g. AES)E K (M),D K (M) – Asymmetric (e.g. RSA)E PK (M),D SK (M) Hash functions (e.g. SHA-3)h(M) Integrity and authentication – Symmetric (MACs)MAC K (M) – Asymmetric (signatures)Sig SK (M),V PK (M) Key agreement Random numbersn = nonce or E -1

15. Questions?