Introduction to Stream Cipher. Sayed Mahdi Mohammad Hasanzadeh [email protected] Spring 2004. Why we need to Cryptography ?. Data transfer algorithm. Source “ Plain text” ABCD… Source coding 100101001010111… Encryption Channel coding Data Transfer.
1) Cryptography remove the redundancy from sequence
2) Cryptography is a mapping in the sequence space
3)Cryptography provide security in some cases: data integrity, Authentication and identification ,…
Pr(Pi=0) Pr(Pi=1) 1/2
Pr(Ci=0) =Pr(Ci=1) =1/2
Pr(ai=0) =Pr(ai=1) =1/2