Network Security

Question 1

What is the goal of confidentiality in network security?

Answer 1

The goal of confidentiality is to ensure that only the sender and intended receiver can understand the message contents. This is typically achieved through encryption by the sender and decryption by the receiver.

Question 2

What is authentication in the context of network security?

Answer 2

Authentication is the process by which the sender and receiver confirm each other’s identities to ensure that communications are secure and trustworthy.

Question 3

Describe a passive attack in network security.

Answer 3

A passive attack involves monitoring the traffic being sent to try to learn secrets, like eavesdropping or snooping, without the user’s knowledge. It is difficult to detect.

Question 4

What is meant by message integrity in network security?

Answer 4

Message integrity refers to the measure taken to ensure that a message is not altered in transit or after receipt without detection.

Question 5

What is a denial of service attack?

Answer 5

A denial of service (DoS) attack aims to make resources (like a server or bandwidth) unavailable to legitimate traffic by overwhelming the resource with bogus traffic.

Question 6

What is symmetric key cryptography?

Answer 6

In symmetric key cryptography, both the sender and receiver share the same secret key, which is used both to encrypt and decrypt messages.

Question 7

What is the Data Encryption Standard (DES)?

Answer 7

DES is an influential symmetric-key encryption algorithm developed in the early 70s that uses a 56-bit key and processes 64-bit plaintext blocks through a series of operations.

Question 8

What replaced DES and why?

Answer 8

The Advanced Encryption Standard (AES) replaced DES because it provides stronger security through longer key lengths (128, 192, or 256 bits) and is efficient in processing data in 128-bit blocks.

Question 9

What is AES and its significance?

Answer 9

AES (Advanced Encryption Standard) is a symmetric-key NIST standard that replaced DES. It is used globally and was adopted by the U.S. government due to its robust security features that render brute force decryption impractical with current technology.

Question 10

What is public key cryptography?

Answer 10

Public key cryptography is an encryption method where the sender and receiver do not share a secret key. Instead, each participant has a pair of keys: a public key known to everyone and a private key known only to the recipient of the messages.

Question 11

What are the main components of a public key encryption system?

Answer 11

In a public key system, there are two main components: an encryption algorithm that uses a public key and a decryption algorithm that uses a corresponding private key.

Question 12

How does RSA encryption work?

Answer 12

RSA encryption involves choosing two large prime numbers, computing their product (n), and a totient (z). A public exponent (e) and a private exponent (d) are then determined. The public key is (n, e) and the private key is (n, d). To encrypt a message (m), compute c = m^e mod n. To decrypt, compute m = c^d mod n.

Question 13

What is the significance of the modulus operation in RSA?

Answer 13

The modulus operation ensures that the calculations of encryption and decryption stay within manageable bounds and are computationally feasible even for very large numbers.

Question 14

Why is it difficult to break RSA encryption?

Answer 14

Breaking RSA encryption typically requires factoring a very large number (n), which is the product of two large primes (p and q). Factoring such a large number is computationally intensive and currently infeasible with conventional technology, making RSA secure.

Question 15

How are symmetric keys used in conjunction with public key cryptography in practice?

Answer 15

Due to the computational intensity of public key operations, they are often used to exchange a symmetric session key securely. Once both parties have the symmetric key, they switch to the faster symmetric key cryptography for regular communications.

Question 16

What modular arithmetic properties are essential for RSA?

Answer 16

Essential properties include the ability to add, subtract, and multiply under modulo operations, which facilitate the encryption and decryption processes by ensuring results remain within the set range.

Question 17

Why does the RSA algorithm work?

Answer 17

RSA works because of properties of modular arithmetic, where the operations of raising messages to the power of the public and private keys, under modulo n, are inverses of each other. This means encrypting with the public key and then decrypting with the private key (or vice versa) retrieves the original message.

Question 18

What are the challenges of implementing RSA?

Answer 18

Key challenges include selecting appropriate key sizes to prevent security vulnerabilities, managing key distribution and storage securely, and handling the computational complexity, especially for very large data transfers.

Question 19

How is the public and private key pair generated in RSA?

Answer 19

The pair is generated by first selecting two large prime numbers. The public key exponent is chosen such that it has no common factors with (p-1)(q-1), and the private key exponent is its modular multiplicative inverse.

Question 20

What are the key steps in generating an RSA public/private key pair?

Answer 20

The steps are: 1) Choose two large prime numbers, p and q.

2) Compute n = pq and z = (p-1)(q-1).

3) Choose an exponent e that is relatively prime to z.

4) Determine d such that (ed mod z = 1). The public key is (n, e) and the private key is (n, d).

Question 21

What is a digital signature?

Answer 21

A digital signature is a cryptographic technique used to verify the authenticity and integrity of a message, software, or digital document. It’s analogous to a hand-written signature but is verifiable and non-forgeable.

Question 22

How does Bob digitally sign a message to Alice?

Answer 22

Bob signs a message by encrypting it with his private key. This creates a “signed” message that can be verified by anyone who has Bob’s public key.

Question 23

How can Alice verify a digitally signed message from Bob?

Answer 23

Alice can verify the signature by decrypting the message using Bob’s public key. If the decrypted message matches the original message sent, it confirms that the message was signed by Bob and has not been altered.

Question 24

What does non-repudiation mean in the context of digital signatures?

Answer 24

Non-repudiation means that the sender (Bob) cannot deny having signed the message, as only his private key could have created the signature that can be verified with his public key.

Question 25

Describe the process Alice uses to send a secure email to Bob.

Answer 25

Alice generates a random symmetric key (KS), encrypts the message with KS for efficiency, then encrypts KS with Bob’s public key. She sends both the encrypted message (KS(m)) and the encrypted key (KB(KS)) to Bob.

Question 26

How does Bob decrypt the secure email sent by Alice?

Answer 26

Bob uses his private key to decrypt and recover the symmetric key (KS). He then uses KS to decrypt the message (KS(m)) to recover the original message (m).

Question 27

How does Alice ensure sender authentication and message integrity in her secure email to Bob?

Answer 27

Alice digitally signs the message by hashing it and then encrypting the hash with her private key. She sends this digital signature along with the message. Bob can verify the signature by decrypting it with Alice’s public key and comparing it with a hash of the received message.

Question 28

How are digital signatures used in secure email communication to provide secrecy, sender authentication, and message integrity?

Answer 28

Alice uses her private key to digitally sign the message for authentication and integrity, encrypts the message content with a symmetric key for secrecy, and encrypts the symmetric key with Bob’s public key to ensure that only Bob can decrypt it.

Question 29

What cryptographic keys does Alice use when sending a secure email?

Answer 29

Alice uses three keys: her private key for signing the message, Bob’s public key for encrypting the symmetric key, and a newly created symmetric key (KS) for encrypting the message itself.

Question 30

What are the benefits of using both symmetric and asymmetric encryption methods in secure email communication?

Answer 30

This dual approach leverages the efficiency of symmetric encryption for encrypting the actual message and the security of asymmetric encryption for safely exchanging the encryption key, ensuring both confidentiality and ease of decryption by the intended recipient.