Alice would like to send confidential and authenticated messages for Bob. Consid
ID: 3888314 • Letter: A
Question
Alice would like to send confidential and authenticated messages for Bob. Consider the following security protocol between Alice, Bob, using a trusted Server. Notation: E(M,K) encryption of message M with key K; D(M,K) decryption of message M with key K; Sign(M,K) signature of message M with key K, KD-X is the private key of X, KE-X is the public key of X, Ksession is a secret key, Id-X is the identity of X, h(M) is the hash value of message M, Timel is a time stamp, and l| denotes a concatenation of the messages. Assume, Alice and Bob know the Server's public key (KE-S) in a reliable manner. Message 1: A®S: "Reqest signed public keys for A and B" Message 2: SBA: Sign(IKE-B | Id-B, KD-S) Sign(IKE-A Il Id-A], KD-S) Why did the Server sign both KE-B and KE-A?Explanation / Answer
Suppose that Alice has to send bob a message using Symmetric Encryption so the steps involved would be :
1) Alice's private key would be used to generate the signature ( encryption using issuer's private-key )
2) The name of the hashing algorithm used by the issuer (alice) will be also attacged to the signature.
3) Now, In order to decrpyt and verify the issuer
Alice's public key and hashing algorithm would be used and then the reciepent has proof that the data was protected and was issued by Alice only .
4) Here we are using Symmetric key algorithms, So the message would be encrypted with signature using SymK ( generated in the process ).
5) SymK will be used by the reciever BOB to decrpyt the message, So in order to make it available to our reciever Bob only we would be encrypting the Symk using the Bob's public key ( which would be available )
The above process will ensure more security amongst the symmetric key encryption also.
I hope it helps
Thank you for reading :)
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