# lec5-4 - Modern Cryptography Lecture 5 Yongdae Kim 2 Admin...

This preview shows pages 1–3. Sign up to view the full content.

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: Modern Cryptography Lecture 5 Yongdae Kim 2 Admin Stuff E-mail Subject should have [5471] in front, e.g. “[5471] Project proposal” CC TA and PostDoc: [email protected], [email protected] Office hours Me: T 1:30 ~ 2:30, Th 10:00 ~ 11:00 (and by appointment) TA: M 1:15 PM ~ 2:15 PM Work on projects Full proposal due: Feb 23 (Firm Deadline: Read instruction) Meeting with groups: This week and next week 3rd assignment is due: 3/2 9:00 AM. Programming, Test vector, Your name Study Guide Come and talk to me and TA as much as possible. (Google chat is good!) Check Calendar 3 Recap Math… Proof techniques Direct/Indirect proof, Proof by contradiction, Proof by cases, Existential/Universal Proof, Forward/backward reasoning Divisibility: a divides b (a|b) if ∃ c such that b = ac GCD, LCM, relatively prime, existence of GCD Eucledean Algorithm d = gcd (a, b) ⇒ ∃ x, y such that d = a x + b y. gcd(a, b) = gcd(a, b + ka) Modular Arithmetic a 㲇 b (mod m ) iff m | a-b iff a = b + mk for some k a 㲇 b (mod m ), c 㲇 d (mod m ) a+c 㲇 ( b+d ) (mod m ), ac 㲇 bd (mod m ) gcd(a, n) =1 a has an arithmetic inverse modulo n. Counting, probability, cardinality, … 4 Recap (cnt) Security Symmetric Key vs. Public Key, Hash function, MAC, Digital signature, Key management through SKE and PKE, certificate Block Cipher Modes of operation and their properties: ECB, OFB, CFB, CBC, CTR Meet-in-the-middle attack and the Double (triple) DES Feistal Cipher and DES 5 New Era! DES broken DES III Challenge by RSA Idle CPU time of around 100,000 computers In 22 hours Triple DES? Original DES was designed for H/W implementation 64 bit block size too small for security and efficiency Now what? 6 Advanced Encryption Standard In 1997, NIST issued a call for proposal Block length = 128 bit Key size = 128, 192, 256 bits In the first round, 15 algorithms were accepted Second round, 5 algorithms were selected In November 2001, final standard was published Rijndel, FIPS PUB 197 http://csrc.nist.gov/publications/fips/fips197/fips-197.pdf Joan Daemen and Vincent Rijmen 7 AES Evaluation Criteria Security Actual security: compared with other submissions Randomness: output is indistinguishable from random Soundness: of mathematical basis Other security factors: raised by security community Cost No licensing: World-wide, non-exclusive, royalty-free Computation efficiency: both S/W and H/W Memory requirements Algorithm and Implementation characteristics Flexibility: key-/block-size, wide variety of platforms Simplicity 8 Stream Cipher Definition encrypt individual characters of plaintext message one at a time, using encryption transformation which varies with time....
View Full Document

## This note was uploaded on 10/21/2011 for the course CSCI 5471 taught by Professor Staff during the Spring '08 term at Minnesota.

### Page1 / 9

lec5-4 - Modern Cryptography Lecture 5 Yongdae Kim 2 Admin...

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document
Ask a homework question - tutors are online