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Prof. Jk LEE/security1 Secure Encryption Systems 암호화복호화 공통비밀키 암호시스템.

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Presentation on theme: "Prof. Jk LEE/security1 Secure Encryption Systems 암호화복호화 공통비밀키 암호시스템."— Presentation transcript:

1 Prof. Jk LEE/security1 Secure Encryption Systems 암호화복호화 공통비밀키 암호시스템

2 Prof. Jk LEE/security2 3.Secure Encryption Systems  Symmetric encryption  Asymmetric encryption  Encryption algorithms DES,RSA and El Gamal  Hash algorithms  Clipper

3 Prof. Jk LEE/security3 Hard Problems:complexity  NP-complete problems:  easy to state,no hard understand, straight forward to solve  satisfiability: true or false  Knapsack: target  Clique: a graph in which each vertex is connected to every other vertex

4 Prof. Jk LEE/security4  Characteristics of NP-complete problems  The class P and NP  NP-completeness and Cryptography

5 Prof. Jk LEE/security5 Properties of Arithmetic  Primes  Greatest common divisor  Modular arithmetic  Properties of Modular Arithmetic  Fermat’s theorem  Algorithm for computing Inverses

6 Prof. Jk LEE/security6  Public key encryption Systems  Proposed by Diffie and Hellman 1976  Merkle-Hellman knapsacks  Rivest-Shamir-Adelman(RSA) Encryption  El Gamal and Digital Signature Algorithms  Hash Algorithms

7 Prof. Jk LEE/security7 Symmetric systems(SS) Symmetric systems(SS)  Single key system-->symmetric system  problem of ss:  if the key revealed?  Distribution of key?  The number of keys increase?  Weak about the attack?

8 Prof. Jk LEE/security8 DES( data Encryption Standard )  Developed by US gov. for use by the general public- 1970.  Plain text:64bit  key: 56bit

9 Prof. Jk LEE/security9 Using Encryption:protocols and Practices

10 Prof. Jk LEE/security10 Distributed center for EI

11 Prof. Jk LEE/security11 Cycles of Substituition and Permutation

12 Prof. Jk LEE/security12 A Cycle in the DES

13 Prof. Jk LEE/security13

14 Prof. Jk LEE/security14

15 Prof. Jk LEE/security15

16 Prof. Jk LEE/security16 Key transformation

17 Prof. Jk LEE/security17

18 Prof. Jk LEE/security18 P-Boxs

19 Prof. Jk LEE/security19

20 Prof. Jk LEE/security20

21 Prof. Jk LEE/security21 Decryption Decryption

22 Prof. Jk LEE/security22 DES 에 관한 우려사항  56 비트 키 사용에 관한 우려  DES 알고리즘의 성질에 관한 우려

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