1) Discuss the security of the following challenge-based scheme for mutual authentication, where Alice (A) and Bob (B) share a secret key K (information below is transmitted asclear text)A-- B: (A, NA. B)/ NA is a nonce chosen by AB-A: (B, Ng. K(NA), A) I Ng is a nonce chosen by BA-B: (A, K(NB). B)2) How would you improve the above schema?

The Needham – Schroeder protocol is one of two important modes of transport intended for use in the…

1) Discuss the security of the following challenge-based scheme for mutual authentication, where Alice (A) and Bob (B) share a secret key K (information below raSMied as clear text) A-B: (A NA. B)/ NA is a nonce chosen by A BA: (8, Ng. K(NA), A) Ng is a nonce chosen by B A-B (A, KINB), B) 2) How would you improve the above schema?

1) Discuss the security of the following challenge-based scheme for mutual authentication, where Alice (A) and Bob (B) share a secret key K (information below raSMied as clear text) A-B: (A NA. B)/ NA is a nonce chosen by A BA: (8, Ng. K(NA), A) Ng is a nonce chosen by B A-B (A, KINB), B) 2) How would you improve the above schema?

Database System Concepts

7th Edition

ISBN:9780078022159

Author:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan

Publisher:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan

Chapter1: Introduction

Section: Chapter Questions

Problem 1PE

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Assume there is a Certificate Authority (CA) with a well-known public key. Further assume every user is issued a certificate for his/her public key. For convenience, we use PKu and SKu to represent user’s public key and private key, respectively. Draw diagrams to answer the following questions. a) Suppose Alice wants to send a large secret message M to Bob. Describe how Alice should send M in an authenticated way. b) Assume Bob receives the message sent by Alice. Describe how Bob should process the message. c) Suppose Alice needs to send a number of large secret messages to Bob. Alice would like to avoid signing digital signatures for all these messages. Develop a protocol for Alice and Bob so that all the messages can be sent in a confidential and authenticated way. Briefly describe the intuition of your protocol first and then draw a diagram.
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Suppose that Alice and Bob communicate using ElGamal cipher and f (p. 9. Z) is common public values. Bob generates his private key d ER Z and then computes the corresponding and public public key y=g" (mod p). To save time, Bob uses the same number r each time he encrypts a plaintext message m (ie., r is a fixed nonce of Bob, and it is not randomly generated each time encryption is performed). Assume that Alice compute the ciphertext for the message m as (cc) = (g mod p, mxy mod p). and for the message m as (1,2)=(g" mod p, xy' mod p). Show how an adversary who possesses a plaintext-ciphertext pair (m. (c.ca)) can decrypt (1, 2) without knowing the private key d of Bob.
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Suppose that you receive a digital certificate that contains M and (h(M)]CA, where M = (Alice, Alice's public key) and "CA" is Certificate Authority. Assuming that you trust the CA, after verifying the signature on the certificate, what do you then know about the identity of the sender of the certificate? Remember that: [Xleob indicates encryption via Bob's private key to X (signature) h(X) indicates the cryptographic hash function applied to X O The sender is Alice O The sender is Trudy I cannot deduce the identity of the sender from the certificate The sender is the Certificate Authority
Suppose that Bob and Alice have access to a public key system that makes their public keys available to each other. KB - and KB + are Bob’s private and public keys, respectively. Each knows its own private key. Describe how Bob and Alice can use these keys so that Bob can know that when he is communication with Alice that he is indeed communicating with Alice. [
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t) Alice and Bob are using the ElGamal cipher with the parameters p 173 and a = 2. = Alice makes the mistake of using the same ephemeral key for two plaintexts, ₁ and 2. The eavesdropper Eve suspects that x₁ 169. She sees the two ciphertexts y₁ = 153 and y2 = 135 in transit; these are the encryptions of ₁ and 2, respectively. a) What is the masking key k? = b) What is the plaintext ₂ ?
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Question 1 Suppose that Bob and Alice have access to public key system that makes their public keys available to each other. KB- and KB+ are Bob's private and public keys, respectively. Each knows its own private key. Describe how Bob and Alice can use these keys so that Bob can know that when he is communication with Alice that is indeed communicating with Alice
Can anyone please explain to me why we have such equations below in part b) and c)? They are the solutions to the questions, but I can't really understand why and how to get that. Many thanks. ==== QUESTION ==== In the Shamir secret sharing scheme, we distribute a secret among q different users as follows. If our secret is a message (m1, . . . , mk) from V (k, q) then, we encode it as a codeword of the Reed-Solomon RSk(q) and give one coordinate to each user. In this problem, we will use q = 7, k = 4 and the parity check matrix H4 below for RS4(7). H4 = [1 1 1 1 1 1 1, 0 1 2 3 4 5 6, 0 1 4 2 2 4 1] a) Write a generator matrix for RS4(7) b) A new secret is selected and user #1 receives share value 0, user #2 receives share value 6 and user #3 receives share value 1 and are collaborating to discover the new secret. Explain why they can’t recover the secret with only this information. c) Now, suppose users #1, #2 and #3 (as in the previous item) discover, in addition to the values of…