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CS707 – Network Security Midterm Exam Questions and Answers 2024
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CS707 – Network Security Midterm Exam Questions and Answers 2024
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CS707 – Network Security Midterm Exam Questions and Answers 2024 Q1 is a symmetric block cipher, uses a 64 bit key, puts the data through 16 rounds of transposition and substitution, and has 5 different modes of operation. • AES • DES • Blowfish • None of above Q2 Examples of asymmetric key algorithms are: • Diffie Hellman, RSA and El-Gamal • RC4, RC5, and RC6 • DES, 3DES, and AES • MD4, MD5, and MD6 Q3 The standard used in digital certificates that defines its structure, fields, and values is • Kerberos • End-to-end encryption • X.509 • The standard used in IPSEC VPNs Q4 A cryptosystem consists of: • Software, algorithms, protocols, and keys • PGP • An algorithm used for encryption and decryption • Is software used for testing security of applications Q5 Cryptanalysis is: • The practice of analyzing secret codes but not breaking them • The technique used by forensic investigators to trace the source of malware infection • The science related to research and development of cryptography • The practice of breaking cryptic systems Q6 An electro -mechanical cipher machine used by the Germans in World War II is • MAC • Enigma • Skytale • All above Q7 A digital signature is best described as: • An electronic verification system used for transactional integrity in banking • A hash value encrypted by the sender’s private key • An electronic verification system used for encryption and hashing • A hash value encrypted with the DES, 3DES, or AES algorithms Q8 A practice of Choosing a key that is extremely random and the algorithm should use the full range of the key -space is called . • Cipher management • Key combination • Key management • None of above Q9 uses two instances of the same key while encrypting and decrypting messages. • Skytale • Symmetric Cryptography • Asymmetric Cryptography • SSL Q10 is a program and protocol used to log in securely to another device or system on a network. • Secure Shell (SSH) • SSL • HTTP • PGP Q11 In Network Security CIA stands for: • Confidentiality, integrity, and. availability • Central Investigation Agency • Confidentiality, Intelligence, and Accountability • Ciphers, Initiation Vectors, Algorithms Q:12 Examples of asymmetric key algorithms are: • Diffie Hellman, RSA and El-Gamal • RC4, RC5, and RC6 • DES, 3DES, and AES • MD4, MD5, and MD6 Q:13 A mathematical function that is easier to compute in one direction than in the other direction, and forms the basis for all asymmetric algorithms • One-Way Function • Two Way Function • A mathematical function used in cryptanalysis • A technique used by forensic experts to lock all hard disk sectors of a computer Q:14 A hash value encrypted by the sender’s private key is • AES • Digital signature • DES • 3DES algorithms Q:15 Cryptanalysis is: The practice of analyzing secret codes but not breaking them • The technique used by forensic investigators to trace the source of malware infection • The science related to research and development of cryptography • The practice of breaking cryptic systems Q:16 Key management is a practice that requires: • Choosing a key that is extremely random and the algorithm should use the full range of the key-space • Labeling keys so that they are not lost or stolen • Returning the key to the CA after it has completed its lifetime • At least two senior officers of the company to issue and maintain a record of the keys Q:17 In end-to-end encryption: • only the header is encrypted, not the payload • Packets do not need to be decrypted and then encrypted at each hop • Only decryption takes place at each hop • The data link and physical layers are involved Q:18 Rootkits are a type of . • Virus • Worm. • Trojan Horse • None of above Q:19 Diffie Hellman is an example of key algorithms. • Symmetric • Asymmetric • Skytale • Enigma Q:20 The standard used in digital certificates that defines its structure, fields, and values is . • X.509 • Kerberose • Cryptography • PKI 2. In context of hashing what is meant by compression. Compression must occur before encryption, because compression is inefficient on encrypted data: compression algorithms work on detecting redundancies and structure in the data, and encryption is designed to hide redundancies and structure. Basically, compression does not work at all on properly encrypted data. Conversely, if compression works on encrypted data, then the encryption layer should be viewed with deep suspicion... When hashing occurs in PGP, it is as part of a signature algorithm, or as an integrity check which is generally known as a MAC. There are several ways to do a MAC; the theoretical "good" way is to apply the MAC on the encrypted data. However, PGP dates from an older time where theory was not yet fully worked out, and uses a hash value (i.e. a function which as no key) and then includes the hash in the encrypted data (see section 5.13 ); the hash value is turned into a MAC by virtue of reusing the encryption key. In the case of such a MAC, the MAC (i.e. the underlying hash) occurs on whatever is encrypted, so that's the compressed data (if compression was used at all). Since you talk about compression "between" the hash and the encryption, then I suppose that you are not talking about that hash at all. Compressing a sequence of characters drawn from an alphabet uses string substitution with no a priori information. An input data block is processed into an output data block comprised of variable length incompressible data sections and variable length compressed token sections. Multiple hash tables are used based on different subblock sizes for string matching, and this improves the compression ratio and rate of compression. The plurality of uses of the multiple hash tables allows for selection of an appropriate compression data rate and/or compression factor in relation to the input data. Using multiple hashing tables with a recoverable hashing method further improves compression ratio and compression rate. Each incompressible data section contains means to distinguish it from compressed token sections. 3. What is X.509 standard? PKI is an ISO authentication framework that uses public key cryptography and the X.509 standard. In cryptography, X.509 is an ITU-T standard for a public key infrastructure (PKI) and Privilege Management Infrastructure (PMI). X.509 specifies, amongst other things, standard formats for public key certificates, certificate revocation lists, attribute certificates , and a certification path validation algorithm . The standard for how the CA creates the certificate is X.509, which dictates the different fields used in the certificate and the valid values that can populate those fields We are currently at version 4 of this standard, which is often denoted as X.509v4. Many cryptographic protocols use this type of certificate, including SSL. The certificate includes the serial number, version number, identity information, algorithm information, lifetime dates, and the signature of the issuing authority. 4. What are one way functions? How they are implemented in cryptography? A one -way function is a mathematical function that is easier to compute in one direction than in the opposite direction. An analogy of this is when you drop a glass on the floor. Although dropping a glass on the floor is easy, putting all the pieces back together again to reconstruct the original glass is next to impossible. This concept is similar to how a one-way function is used in cryptography, which is what the RSA algorithm, and all other asymmetric algorithms, is based upon. The easy direction of computation in the one-way function that is used in the RSA algorithm is the process of multiplying two large prime numbers. Multiplying the two numbers to get the resulting product is much easier than factoring the product and recovering the two initial large prime numbers used to calculate the obtained product, which is the difficult direction. RSA is based on the difficulty of factoring large numbers that are the product of two large prime numbers. Attacks on these types of cryptosystems do not necessarily try every possible key value, but rather try to factor the large number, which will give the attacker the private key. When a user encrypts a message with a public key, this message is encoded with a one -way function (breaking a glass). This function supplies a trapdoor (knowledge of how to put the glass back together), but the only way the trapdoor can be taken advantage of is; if it is known about and the correct code is applied. The private key provides this service. The private key knows about the trapdoor, knows how to derive the original prime numbers, and has the necessary programming code to take advantage of this secret trapdoor to unlock the encoded message (reassembling the broken glass). Knowing about the trapdoor and having the correct functionality to take advantage of it are what make the private key private.The benefits of buying summaries with Stuvia:
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