Online Cryptography Course Dan Boneh Introduc/on Course Overview Dan Boneh Welcome Course objec/ves: • Learn how crypto primi/ves work • Learn how to use them correctly and reason about security My recommenda/ons: • Take notes • Pause video frequently to think about the material • Answer the in-‐video ques/ons Dan Boneh Cryptography is everywhere Secure communica,on: – web traffic: HTTPS – wireless traffic: 802.11i WPA2 (and WEP), GSM, Bluetooth Encryp,ng files on disk: EFS, TrueCrypt Content protec,on (e.g DVD, Blu-‐ray): CSS, AACS User authen,ca,on … and much much more Dan Boneh Secure communica/on no eavesdropping no tampering Dan Boneh Secure Sockets Layer / TLS Two main parts Handshake Protocol: Establish shared secret key using public-‐key cryptography (2nd part of course) Record Layer: Transmit data using shared secret key Ensure confiden/ality and integrity (1st part of course) Dan Boneh Protected files on disk Disk Alice File 1 File 2 Alice No eavesdropping No tampering Analogous to secure communica/on: Alice today sends a message to Alice tomorrow Dan Boneh Building block: sym encryp/on Alice m E Bob E(k,m)=c c D D(k,c)=m k k E, D: cipher k: secret key (e.g 128 bits) m, c: plaintext, ciphertext Encryp/on algorithm is publicly known • Never use a proprietary cipher Dan Boneh Use Cases Single use key: (one /me key) • Key is only used to encrypt one message • encrypted email: new key generated for every email Mul, use key: (many /me key) • Key used to encrypt mul/ple messages • encrypted files: same key used to encrypt many files • Need more machinery than for one-‐/me key Dan Boneh Things to remember Cryptography is: – A tremendous tool – The basis for many security mechanisms Cryptography is not: – The solu/on to all security problems – Reliable unless implemented and used properly – Something you should try to invent yourself • many many examples of broken ad-‐hoc designs Dan Boneh End of Segment Dan Boneh