Chapter 7: Cryptography and the PKI

Mike is sending David an encrypted message using an a symmetric encryption algorithm. What key should he use to encrypt the message?

• Mike's public key

• Mike's private key

• David's public key

• Shared secret key

Answer explanation

Key Phrase: "encrypted message using an a symmetric encryption algorithm"

Explanation:
Correct Answer (D): In symmetric encryption algorithms, both the sender and the receiver use a shared secret key to encrypt and decrypt the message.
Why others are wrong:

• A: Mike’s public key would not be used by Mike himself for encryption.

• B: Mike’s private key would be used for signing, not encryption.

C: Encrypting with the David’s public key is a asymmetric encryption, where only the David can decrypt it using his private key.

Shahl has recently discovered an attack where the attacker managed to force a network user to use weak encryption and was then able to decrypt that content. What term best describes this attack?

• Downgrade

• Collision

• Homomorphic encryption

• Birthday attack

Answer explanation

Key Phrase: "force a network user to use weak encryption"

Explanation:
Correct Answer (A): A downgrade attack forces a system to use weaker encryption than originally intended, making it easier to break the encryption.
Why others are wrong:

• B: A collision occurs when two different inputs produce the same hash value, not relevant in this scenario.

• C: Homomorphic encryption is a technique that allows computation on encrypted data, not an attack.

• D: A birthday attack is a type of attack on hash functions, unrelated to encryption strength.

Norm is using full-disk encryption technology to protect the contents of laptops against theft. What goal of cryptography is he attempting to achieve?

• Integrity

• Non-repudiation

• Authentication

• Confidentiality

Answer explanation

Key Phrase: "full-disk encryption technology"

Explanation:
Correct Answer (D): Full-disk encryption is designed to protect the confidentiality of the data by ensuring that unauthorized users cannot access it.
Why others are wrong:

• A: Integrity ensures that data hasn’t been altered.

• B: Non-repudiation prevents someone from denying their actions, unrelated to encryption.

• C: Authentication verifies the identity of users but is not the main goal here.

Brian discovers that a user suspected of stealing sensitive information is posting many image files to a message board. What technique might the individual be using to hide sensitive information in those images?

• Steganography

• Homomorphic encryption

• Replay attack

• Birthday attack

Answer explanation

Key Phrase: "hiding sensitive information in those images"

Explanation:
Correct Answer (A): Steganography is the practice of hiding information within other non-suspicious content, like images.
Why others are wrong:

• B: Homomorphic encryption protects data while allowing computations but doesn't hide it in files.

• C: A replay attack involves capturing and reusing data; it doesn’t hide data in files.

• D: A birthday attack is related to hash collisions, not hiding information.

Which one of the following statements about cryptographic keys is incorrect?

• All cryptographic keys should be kept secret.

• Longer keys are better than shorter keys when the same algorithm is used.

• Asymmetric algorithms generally use longer keys than symmetric algorithms.

• Digital certificates are designed to share public keys.

Answer explanation

Key Phrase: "incorrect statement about cryptographic keys"

Explanation:
Correct Answer (A): Not all cryptographic keys need to be secret. Public keys, used in asymmetric encryption, should be freely shared.
Why others are wrong:

• B: Longer keys are generally more secure in the same algorithm.

• C: Asymmetric algorithms use longer keys than symmetric ones.

• D: Digital certificates are used to share public keys securely.

What type of cipher operates on one character of text at a time?

• Block cipher

• Bit cipher

• Stream cipher

• Balanced cipher

Answer explanation

Key Phrase: "operates on one character of text at a time"

Explanation:
Correct Answer (C): A stream cipher encrypts one bit or character at a time.
Why others are wrong:

• A: A block cipher encrypts chunks of data at a time, not one character.

• B: Bit ciphers are a type of stream cipher but focus on bits, not characters.

• D: There is no such thing as a "balanced cipher."

Vince is choosing a symmetric encryption algorithm for use in his organization. He would like to choose the strongest algorithm from these choices. What algorithm should he choose?

• DES

• 3DES

• RSA

• AES

Answer explanation

Key Phrase: "strongest a symmetric encryption algorithm"

Explanation:
Correct Answer (D): AES is strongest for symmetric encryption tasks.
Why others are wrong:

• A: DES is outdated and considered insecure.

• B: 3DES is stronger than DES but weaker than AES.

• C: RSA is a strong asymmetric algorithm, but it’s typically slower than AES.

Kevin is configuring a web server to use digital certificates. What technology can he use to allow clients to quickly verify the status of those certificates without contacting a remote server?

• CRL

• OCSP

• Certificate stapling

• Certificate pinning

Answer explanation

Key Phrase: "verify the status of certificates without contacting a remote server"

Explanation:
Correct Answer (C): Certificate stapling allows the server to send a recent OCSP response with the certificate, allowing clients to verify the certificate status without contacting a remote server.
Why others are wrong:

• A: Certificate revocation lists (CRLs) are a slower, outdated approach to managing certificate status.

• B: The Online Certificate Status Protocol(OCSP) provides real- time checking of a digital certificate's status using a remote server.

• D: Certificate pinning is used to provide an expected key, not to manage certificate status.

Acme Widgets has 10 employees and they all need the ability to communicate with one another using a symmetric encryption system. The system should allow any two employees to securely communicate without other employees eavesdropping. If an 11th employee is added to the organization, how many new keys must be added to the system?

• 1

• 2

• 10

• 11

Answer explanation

Key Phrase: "symmetric encryption system"

Explanation:
Correct Answer (C): In symmetric encryption, each pair of employees needs a unique shared key. With 10 employees, there are 10 pairs, and adding an 11th employee requires 10 new keys.
Why others are wrong:

• A: Only 1 key is needed to add the 11th employee, but symmetric encryption requires more.

• B: 2 keys are required for the pair, not for everyone.

• D: 11 keys are too many; only 10 are needed.

Referring to the scenario in question 9, if Acme Widgets switched to an asymmetric encryption algorithm, how many keys would be required to add the 11th employee?

• 1

• 2

• 10

• 11

Answer explanation

Key Phrase: "asymmetric encryption algorithm"

Explanation:
Correct Answer (B): In asymmetric encryption, each user needs two keys: a public and a private key. Adding an 11th employee requires only 2 new keys (one pair).
Why others are wrong:

• A: Only 1 key is needed, but asymmetric encryption needs both public and private keys.

• C: 10 keys are already present, but only 2 are needed for the new employee.

• D: 11 keys are excessive.