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Unformatted text preview: Comments on Chapter 7 Who does what using whose keys? Suppose there are a number of users in the communication network (such as the internet). Let them be user 1 , 2 , 3 , , etc. Each user i has to pick his/her own public and private keys. So, each will pick p i , q i , and calculate N i = p i q i and e i coprime to ( p i 1)( q i 1), and d i satisfying e i d i 1 mod ( p i 1)( q i 1). For example, if there are 100 users, there will be 100 pairs of public and private keys. Suppose user i wants to send a message M to user j . To encrypt, user i encrypts by using user j s public key ( e j , N j ). To decrypt, user j decrypts by using his/her own private key ( d j , N j ). To sign, user i uses his own private key ( d i , N i ). We can understand, rather than remember all these. A message is encrypted for a specific receiver, but every sender has follows the same encryption procedure. So, it must use the receivers key. Furthermore, everyone can do it, so, it must use the public key. Likewise, only the receiver can decrypt. So, decryption must use the private key of the receiver. Now, a signature has nothing to do with the receiver, and verifies who is the sender. So, it has to use the senders key, and since only the sender can sign, it has to use the private key. Whats in the last half page of Chapter 7 (p 179) concerning digital signature? It assumes knowledge of Chapter 6. We summary the concepts here....
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This note was uploaded on 04/13/2010 for the course MATH 135 taught by Professor Andrewchilds during the Spring '08 term at Waterloo.
 Spring '08
 ANDREWCHILDS

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