Nt1310 Unit 4 Case Study

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Question 1 Yes, each user maintaining their own secret key is more secure than all three of them sharing the same key. For this scenario to work correctly, knowledge of a shared secret key must be used. For example, if Alice wants to talk to Carol, they must both have knowledge of a key KAC. First Alice will generate a random challenge, C1, to send to Carol. Carol will compute a message digest of the challenge C1 and the shared key KAC, and reply to Alice. Carol will also send another challenge, C2, to Alice. Alice will do the same thing with C2 and KAC, and send the response to Carol. When each recipient receives the challenge-response, they can compare it with their own digest of their challenge and the shared secret key. This allows for both one-way and mutual authentication between the two parties (Slides 05). Each party can verify the intended recipient without relaying any kind of passphrase or secret key over the network. Although this method is more secure for the sake of not sharing secret keys among each client, it is still susceptible to reflection and replay attacks. Simple challenge-response provides data-origin authentication, but does not provide non-repudiation (Slides 05). Further …show more content…

The fundamental problem with this is RSA requires the message being signed to be smaller than n. To generate the public key, a number e is chosen that is relatively prime to φ(n) which is equal to (p-1)(q-1). The private key is a number d that is the multiplicative inverse of e mod φ(n) (Kaufman, Perlman & Speciner, 2002). The book continues on to say “[t]o encrypt a message m (<n) with signature s=md mod n based on your private key” (Kaufman, Perlman & Speciner, 2002). This means that if a message m is larger than n, the raw message itself and m mod n would have the same

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