CYSE 610 Midterm Exаm Tоtаl 110 pоints Nаme (first and last, as shоwn in Blackboard): ______________ Multiple choice. Each question only has one correct answer. 3 points each. In the following four layers, which one is the lowest of the four according to the OSI 7-layer model, consider the physical layer is at the bottom layer? Session layer Transport layer Network layer Data link layer Which of the following protocols helps the translation between a public IP address, such as 12.23.34.45 to a private IP address, such as 192.168.0.131? DNS NAT ICMP TCP As shown in the following picture, Host B sends a message to Host A. When the message is being transmitted on the section between the router R and Host A, what is the source MAC address of this message? 74-29-9C-E8-FF-55 1A-23-F9-CD-06-9B E6-E9-00-17-BB-4B 49-BD-D2-C7-56-2A Monoalphabetic cipher is the type of cipher where one letter is mapped to another arbitrary letter (without overlapping). For the English alphabet with 26 letters, how many different mapping schemes are there? 26 2626 26 * 26 26! Is the following a correct statement regarding Hash? Alice generates a message m, and Hash of the message H(m). Alice sends both m and H(m) to Bob. On receiving it, Bob calculates the Hash of m, and then compares the calculated hash value with the received H(m). If they match, Bob concludes the message has not been modified along the way. Yes, this statement is correct, and Bob can ensure the message has not changed as long as the two Hashes match. No, this statement is not correct, and Bob cannot ensure the message has not changed even if the two Hashes match. There is a symmetric cryptography algorithm whose key length is 128 bits. If we chain the algorithm twice, i.e., encrypt plaintext twice using this algorithm but with two different keys, what is the equivalent key length of the chained algorithm? 128 bits 129 bits 127 bits 255 bits The following figure is the Cipher Block Chaining (CBC) mode to encrypt large messages. Which of the followings statement is correct regarding this mode? If a message contains two identical 64-bit blocks, the corresponding ciphertext will also be identical. Switching the order of two cipher blocks will not cause any detectable error in the plaintext. Duplicating a block will not cause any detectable error in the plaintext. Deleting a block will cause some detectable error in the plaintext. Which of the following statement regarding Diffie-Hellman is incorrect? All the messages exchanged between Alice and Bob can be exposed to Trudy, but Trudy cannot infer the shared secret between Alice and Bob. Alice and Bob must already have a pre-shared secret in order to use Diffie-Hellman. Diffie-Hellman is subject to the Man-in-the-middle attack. Neither Alice nor Bob needs to reveal their own secret to the other party. “Given a message m1, it should be computationally infeasible to find a different message m2, such that H(m1) = H(m2)”, this statement refers to which property of Hash function? Preimage resistance Collision resistance Second preimage resistance Third preimage resistance Alice and Bob would like to communicate with each other using cryptography to protect the confidentiality of their communications. They exchanged digital certificates, which were issued by a CA, to begin this process, and they plan to use asymmetric encryption algorithm for the secure exchange of messages. Whose key should be used to encrypt Alice’s and Bob’s digital certificate? Alice’s public key Alice’s private key Bob’s public key Bob’s private key CA’s public key CA’s private key Based on the previous question, when Alice sends Bob a message, which key should Alice use to encrypt the message? Alice’s public key Alice’s private key Bob’s public key Bob’s private key CA’s public key CA’s private key Based on the previous question, Alice would like to enhance the security of her communication by adding a digital signature to the message. What goal of cryptography are digital signatures intended to enforce? Secrecy Availability Confidentiality Nonrepudiation Which method in the following is NOT a countermeasure against online password guessing? Lock the account if the password is entered incorrectly 5 times After 3 times of incorrect password, the system enforces CAPTCHA (see the following image if you are not familiar with CAPTCHA) Store the Hash of user password with salt Send a text message to the user’s phone if a password is entered incorrectly 3 times In a network whose authentication is build based on PKI, what will be the consequence if the Certification Authority (CA) stopped working? No one can start new session with others, existing sessions are not affected. No new sessions can be started, and all existing sessions become unsecure and should be immediately terminated. Those with a valid certificate can still start new sessions with others, those without a valid certificate can’t start new sessions because they can’t obtain a valid certificate. There will not be any impact at all because the CA dose not need to be online at all. Whose key is used to encrypt the Ticket Granding Ticket (as in Kerberos)? Alice’s master secret Bob’s master secret KDC’s master secret CA’s master secret During the TLS handshake, both Alice and Bob send a “keyed Hash of previously exchanged messages”, what is the purpose of sending such messages? For Alice and Bob to authenticate each other. For Alice and Bob to proof to each other that they know the secret key. For Alice and Bob to verify that there were no man in the middle during the initial message exchange. For Alice and Bob to inform each other that they are ready to start the communication. Short answer questions: Please write legibly and list only the essentials, excessive description will not earn extra points. And we reserve the right to refuse grading if we can not recognize your handwriting. (8 pts) The following figure shows the design of 3DES. As shown in this figure, even though the encryption goes through 3 operations (encryption, decryption, and then encryption), it only uses 2 keys instead of 3 keys. Won’t it be more secure if we use three different keys, that is, K1, K2, K3, instead of K1, K2, K1? Briefly explain your reason. (9 pts) Design a simple communication protocol where Alice authenticates herself to Bob (i.e., one way authentication only), using a public key algorithm, a secret key algorithm, and a hash algorithm. Your answers MUST include: A line-and-arrow diagram, as we used in the slides, that shows the message exchange between Alice and Bob. Associate the lines with appropriate and legit message content. A brief explanation of the content of each message. Authentication using a public key algorithm (assume Alice and Bob both have a public/private key pair, and they have already known each other’s public key) Authentication using a secret key algorithm (assume Alice and Bob have a pre-shared secret) Authentication using a Hash algorithm (Assume Alice and Bob have a pre-shared secret) (8 pts) Choose p = 11, q = 17, and e = 7. Find out the RSA private key . You must show all your steps to get full credit. (8 pts) Briefly explain how do KDC and CA works by comparing KDC and CA from the following four perspectives. What secrets does a KDC/CA have. In a KDC/CA network, if two hosts want to communicate securely, how are they going to establish a shared secret. What are the consequences if a KDC/CA stopped working. What are the consequences if a KDC/CA is compromised by an attacker and all stored secrets are stolen. (8 pts) The following authentication protocol is subject to the reflection attack. Explain how does a reflection work. Your answer must include a block-and-arrow diagram and verbal explanation. What modification can make it on longer vulnerable to the reflection attack? (12 pts) Explain what is Perfect Forward Secrecy, do the following protocols have perfect forward secrecy, why or why not? Explain what is perfect forward secrecy. Alice and Bob have a shared secret K. Alice generates a random value R and sends (R)K to Bob. Alice and Bob use R as the session key to exchange data and both forget R when the session is finished. Alice and Bob both have a public/private key pair and know each other’s public key. Alice generates a random value R, and send (R)Kb+ to Bob. Alice and Bob use R as the session key to exchange data and both forget R when the session is finished. Alice and Bob both have a public/private key pair and know each other’s public key. Alice generates a pair of public/private keys, K+ and K-, and sends K+ to Bob. Bob generates a random value R, and sends (R)K+ to Alice. Alice and Bob use R as the session key to exchange data and both forget R, K-, and K+ when the session is finished. (9 pts) The following protocol is a strong password protocol. Explain: What does it mean to be a strong password protocol, why do we need such protocols? Why is this protocol a strong password protocol? Explain what is the difference between the strong password protocol and the credentials download protocol?
Why is tаking pаrоxetine (Pаxil) cоnsistently and never running оut of medication more important with this drug.
The Mоrmоns were led intо the Utаh Territory by Joseph Smith.