Network Security Chapter 8
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Questions and Answers

What are the four main criteria of network security?

Confidentiality, Authentication, Message Integrity, and Access and Availability

What is the purpose of encryption and decryption in network security?

To ensure confidentiality, where only the sender and intended receiver can understand the message contents

Who are Alice, Bob, and Trudy in the context of network security?

Alice is the sender, Bob is the receiver, and Trudy is an intruder who might intercept, delete, or add messages

What are some examples of real-life Bobs and Alices in network security?

<p>Web browser/server for electronic transactions, on-line banking client/server, DNS servers, routers exchanging routing table updates, etc.</p> Signup and view all the answers

What is the purpose of authentication in network security?

<p>To confirm the identity of the sender and receiver to each other</p> Signup and view all the answers

What is the role of Trudy in network security scenarios?

<p>Trudy is an intruder who might intercept, delete, or add messages during transmission</p> Signup and view all the answers

What is eavesdropping in the context of network security?

<p>intercepting messages</p> Signup and view all the answers

What is hijacking in the context of network security?

<p>taking over an ongoing connection by removing the sender or receiver and inserting oneself in place</p> Signup and view all the answers

What is the main difference between symmetric key crypto and public-key crypto?

<p>symmetric key crypto uses a single key for encryption and decryption, while public-key crypto uses a public key for encryption and a secret key for decryption</p> Signup and view all the answers

What is the purpose of cryptography in network security?

<p>to protect data from unauthorized access</p> Signup and view all the answers

What is the main advantage of public-key crypto over symmetric key crypto?

<p>public-key crypto allows for secure key exchange over an insecure channel</p> Signup and view all the answers

What is the difference between encryption and decryption in cryptography?

<p>encryption is the process of converting plaintext into ciphertext, while decryption is the process of converting ciphertext back into plaintext</p> Signup and view all the answers

What is the methodology used to encrypt plaintext in the given example?

<p>Each letter of the plaintext is converted to its number, then the value for the key is added, and the resulting number is converted back to a letter.</p> Signup and view all the answers

What is the role of the key value in symmetric key cryptography?

<p>The key value is added to the plaintext number to get the ciphertext, and subtracted from the ciphertext to get the plaintext back.</p> Signup and view all the answers

What is the Caesar Cipher, and how does it work?

<p>The Caesar Cipher is a monoalphabetic rotation cipher, where each letter of the plaintext is rotated forward three times to encrypt.</p> Signup and view all the answers

What is the difference between symmetric and asymmetric key cryptography?

<p>In symmetric key cryptography, Bob and Alice share the same key, whereas in asymmetric key cryptography, they do not.</p> Signup and view all the answers

How does the ASCII character representation work?

<p>Each character can be represented using 8, 16, 24, or 32 bits, depending on the system.</p> Signup and view all the answers

What is DES, and what are its key characteristics?

<p>DES is the Data Encryption Standard, a US encryption standard that uses a 56-bit symmetric key and 64-bit plaintext input.</p> Signup and view all the answers

What is the problem with key agreement in symmetric key cryptography?

<p>The problem is how Bob and Alice agree on the key value without actually exchanging it.</p> Signup and view all the answers

How do you decrypt a ciphertext in symmetric key cryptography?

<p>You subtract the key value from the ciphertext to get the plaintext back.</p> Signup and view all the answers

How are public keys typically made available to users?

<p>Through a publicly accessible repository or directory</p> Signup and view all the answers

What is an additional property of public-key ciphers?

<p>The private decryption key can be used with the encryption algorithm to encrypt messages</p> Signup and view all the answers

What is the purpose of using the private decryption key to encrypt messages in public-key cryptography?

<p>Authentication</p> Signup and view all the answers

What type of cipher substitutes one letter for another?

<p>Monoalphabetic cipher</p> Signup and view all the answers

What is the difference between plaintext and ciphertext in a cipher?

<p>Plaintext is in lowercase letters, and ciphertext is in uppercase letters</p> Signup and view all the answers

Why are spaces often removed in the ciphertext of a monoalphabetic cipher?

<p>To make attacking the ciphertext more difficult</p> Signup and view all the answers

What is an example of a monoalphabetic cipher?

<p>Shift cipher</p> Signup and view all the answers

How can a monoalphabetic cipher like the one shown be broken?

<p>Brute force</p> Signup and view all the answers

What is the significance of the DES Challenge in the context of network security?

<p>The DES Challenge demonstrates that a 56-bit-key-encrypted phrase can be decrypted using brute force in 4 months, highlighting the limitations of DES encryption.</p> Signup and view all the answers

How does the DES operation work?

<p>The DES operation involves an initial transformation, followed by 16 identical rounds of function application, each using different 48 bits of the key, and finally a final transformation.</p> Signup and view all the answers

What is the purpose of using three keys sequentially in 3-DES encryption?

<p>Using three keys sequentially in 3-DES encryption makes it more secure by increasing the difficulty of brute force decryption.</p> Signup and view all the answers

What is the main difference between DES and AES encryption?

<p>AES encryption processes data in 128-bit blocks, whereas DES processes data in 64-bit blocks, and AES uses 128, 192, or 256-bit keys, whereas DES uses 56-bit keys.</p> Signup and view all the answers

How does block cipher chaining work?

<p>In block cipher chaining, each input block is XORed with the previous block of cipher text, producing a unique cipher text for each block.</p> Signup and view all the answers

What is the purpose of transmitting the initial cipher block in clear in cipher block chaining?

<p>The initial cipher block is transmitted in clear to the receiver, allowing them to decrypt the message.</p> Signup and view all the answers

What would happen in the 'HTTP/1.1' scenario if cipher block chaining were not used?

<p>If cipher block chaining were not used, the same input block 'HTTP/1.1' would produce the same cipher text, making it vulnerable to attacks.</p> Signup and view all the answers

What is the significance of the number of rounds in DES encryption?

<p>The 16 rounds of function application in DES encryption ensure that each input bit affects all output bits, making it more secure.</p> Signup and view all the answers

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