1. Class 4 Asymmetric Cryptography and Trusting Internal Components CIS 755: Advanced Computer Security Spring 2014 Eugene Vasserman http://www.cis.ksu.edu/~eyv/CIS755_S14/

2. Administrative stuff Quiz on Thursday – Cryptography concepts – Examples… Project due dates posted Schedule always being updated – watch for changes What would you like to see covered? Paper reading and the “huh?” moment

3. Last time: Basic primitives Confidentiality (encryption) – Symmetric (e.g. AES) – Asymmetric (e.g. RSA) Hash functions Integrity and authentication – Symmetric (authentication codes) – Asymmetric (signatures) Random numbers

4. Asymmetric cryptography The idea: base security properties on mathematical statements – Facts or assumptions We need to be familiar with our toolset NEVER BUILD YOUR OWN WHEN SOLUTION EXISTS!!

5. NEVER BUILD YOUR OWN WHEN SOLUTION EXISTS!!!

6. Asymmetric No pre-shared keys Public and secret keys (key pairs) Asymmetric means…? – Non-repudiable Key agreement, e.g. Diffie-Hellman – Not like sending password in the clear Mathematical proof based on conjecture – Variants of conjecture (important)

7. Security (strength) Key size * – Commonly 2 256 for AES, 2 2048 for RSA – What is a [good] key? Underlying cryptosystem/primitives Composition e.g. MAC with broken underlying hash function may not itself be broken

8. Current state of symmetric encryption DES is too weak (56-bit key) 3DES is weak (168-bit keys but only 2 112 security – “meet-in-the-middle” attack) Recent weaknesses in AES: – AES-256 (2 254.4 ) AES-192 (2 189.7 ) AES-128 (2 126.1 ) http://research.microsoft.com/en- us/projects/cryptanalysis/aesbc.pdf

9. Current state of hash functions MD5 is broken – http://www.win.tue.nl/hashclash/ http://www.win.tue.nl/hashclash/ SHA-1 is known to be weak – http://theory.csail.mit.edu/~yiqun/shanote.pdf (2 69 ) http://theory.csail.mit.edu/~yiqun/shanote.pdf – http://eprint.iacr.org/2004/304 (2 106, generalizable) http://eprint.iacr.org/2004/304 – SHA-256 (variant) is even weaker SHA-3 currently in “development” (NIST) – We have a winner: all hail Keccak (SHA-3)! – http://csrc.nist.gov/groups/ST/hash/sha-3/ http://csrc.nist.gov/groups/ST/hash/sha-3/

10. Questions? Trusted component discussion