a7sp06solutions - CS 414 Assignment 7 5 points per answer...

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CS 414 Assignment 7 5 points per answer for 1a-c, 4a-c and 10 points per answer for 2, 3 (50 max). Due Friday May 5. 1. Discuss how public key cryptography can be used to achieve the following goals. (a) Authentication: the receiver knows that only the sender could have generated message. Solution Let A be the sender and B be the receiver. Let E A , E B and D A , D B denote the en- cryption and decryption functions corresponding to A and B respectively. A sends M, E A ( h ( M )) (where h is a hash function - universally known) to B . (b) Secrecy: only the receiver can decrypt the message. Solution A sends K AB ( M ) , D B ( K AB ) ( D x can be computed by anyone using the public key of x ) to B (where K AB ( m ) is symmetric encryption using the key K AB ). (c) Authentication and secrecy: only the receiver can decrypt the message, and the receiver knows that only the sender could have generated the mssage. Solution A sends K AB ( M, E A ( h ( M ))) , D B ( K AB ) to B . 2. Some operating systems have a feature that allows for encrypting the filesystem, either in whole or in part. This encryption is done at the filesystem level, and programs running on the system never
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