Presentation is loading. Please wait.

Presentation is loading. Please wait.

Introduction to Stream Cipher Sayed Mahdi Mohammad Hasanzadeh Spring 2004.

Similar presentations


Presentation on theme: "Introduction to Stream Cipher Sayed Mahdi Mohammad Hasanzadeh Spring 2004."— Presentation transcript:

1 Introduction to Stream Cipher Sayed Mahdi Mohammad Hasanzadeh Hasanzadeh@Raymandcrypto.ir Spring 2004

2 Why we need to Cryptography ?

3 Data transfer algorithm 1) Source  “Plain text” ABCD… 2) Source coding  100101001010111… 3) Encryption 4) Channel coding 5) Data Transfer

4 Why we need to Cryptography We have redundancy in every language Pr(A)  Pr(B)  Pr(C)  …  Pr(Z) Plain text redundancy leakage to Source Coding => Pr(1)  Pr(0)  ½ Attacker guesses some of the bites from sequence Then attacker guesses the plain text

5 Goals in cryptography 1) Cryptography remove the redundancy from sequence Pr(1)=Pr(0)=1/2 2) Cryptography is a mapping in the sequence space 3)Cryptography provide security in some cases: data integrity, Authentication and identification,…

6 Tools in Cryptography Symmetric encryption Hash functions Message authentication codes Random number generators Public-key encryption Digital signatures Authentication and identification Key establishment, management, and certification

7 Symmetric Encryption There are basically two ways to make a symmetric cipher: Stream cipher: The encryption rule depends on the plaintext symbol’s position in the stream of plaintext symbols. e.g.: Vigenere, RC4, A5 Block cipher: Encrypt several plaintext symbols at once in a block. e.g.: DES, AES, Twofish, RC6

8 Stream Cipher Pr(Ci=0) =Pr(Ci=1) =1/2 Pr(Pi=0)  Pr(Pi=1)  1/2 Pr(ai=0) =Pr(ai=1) =1/2

9 Generator Properties Randomness Provable security Bit rate Key length Complexity of algorithm Memory Resistant against every attack


Download ppt "Introduction to Stream Cipher Sayed Mahdi Mohammad Hasanzadeh Spring 2004."

Similar presentations


Ads by Google