Lecture2-Study

# Lecture2-Study - Technology ITEC443 Lecture2Questions...

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Lecture 2- Questions Eastern Mediterranean University School of Computing and  Technology ITEC 443 Cryptography and Network Security

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Review Questions 2.1  What are the essential ingredients of a  symmetric cipher? Solution Plaintext,  Encryption algorithm,  Secret key,  Ciphertext,  Decryption algorithm. Dr. E. Iscioglu                                                 Cryptography and Network Security 2
Review Questions 2.3  How many keys are required for two  people to communicate via a cipher?  Solution: One key for symmetric ciphers,  Two keys for asymmetric ciphers. Dr. E. Iscioglu                                                 Cryptography and Network Security 3

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Review Questions 2.4  What is the difference between a block  cipher and a stream cipher?  Solution: stream cipher  is one that encrypts a  digital data stream one bit or one byte at a  time. block cipher  is one in which a block of  plaintext is treated as a whole and used to  produce a ciphertext block of equal length. Dr. E. Iscioglu                                                 Cryptography and Network Security 4
Review Questions 2.5  What are the two general approaches  to attacking a cipher?   Solution: Cryptanalysis and brute force. Dr. E. Iscioglu                                                 Cryptography and Network Security 5

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Review Questions 2.5  What is the difference between an unconditionally  secure cipher and a computationally secure cipher?  Solution: An encryption scheme is  unconditionally secure  if  the ciphertext generated by the scheme does not  contain enough information to determine uniquely the  corresponding plaintext, no matter how much  ciphertext is available.  An encryption scheme is said to be  computationally  secure  if: (1) the cost of breaking the cipher exceeds  the value of the encrypted information, and (2) the  time required to break the cipher exceeds the useful  lifetime of the information. Dr. E. Iscioglu                                                 Cryptography and Network Security 6
Review Questions 2.8  Briefly define the Caesar cipher. 2.9  Briefly define the monoalphabetic cipher. 2.10  Briefly define the Playfair cipher.

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Lecture2-Study - Technology ITEC443 Lecture2Questions...

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