Consider a public key encryption. Ann wants to send Bill a message. Let Annpriv
ID: 3681231 • Letter: C
Question
Consider a public key encryption. Ann wants to send Bill a message. Let Annpriv and Annpub be Ann’s private and public keys respectively. The same for Bill (Billpriv and Billpub). (a) If Ann sends a message to Bill, what encryption should Ann use so that only Bill can decrypt the message (secrecy)? (b) Can Ann encrypt the message so that anyone who receives the message is assured that the message only came from Ann (authenticity)? (c) Is it possible for Ann to devise a method that will allow for both secrecy and authenticity for her message? Please justify your answer.
Explanation / Answer
a) Ann must first encrypt her message with private key Annpriv. The recieved encrypted message then will be decrypted by Bill using his public key Billpub.
b) Yes, the authencity will be provided assuring the reciever that the message is sent by Ann only, because the message sent by Ann can be encrypted with her private key which will be only with her.
c) Yes, it is possible for Ann to devise a method that will allow for both secrecy and authenticity for her message. the method is know as envelope method which is hybrid method for providing authenticated encryption.This method uses Public Key Encryption and Digital Signatures for providing Security and Encryption.
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