1 / 9

Introduction to Stream Cipher

Introduction to Stream Cipher. Sayed Mahdi Mohammad Hasanzadeh Hasanzadeh@Raymandcrypto.ir Spring 2004. Why we need to Cryptography ?. Data transfer algorithm. Source  “ Plain text” ABCD… Source coding  100101001010111… Encryption Channel coding Data Transfer.

bree
Télécharger la présentation

Introduction to Stream Cipher

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

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

  2. Why we need to Cryptography ?

  3. Data transfer algorithm • Source  “Plain text” ABCD… • Source coding  100101001010111… • Encryption • Channel coding • 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(Pi=0) Pr(Pi=1) 1/2 Pr(Ci=0) =Pr(Ci=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

More Related