Question 1

For symmetric encryption to work the two parties to an exchange must share the same key and that key must be protected from access by others.

Accepted Answer

This is the basic principle of symmetric encryption. The same key is used by both parties to encrypt and decrypt the message, so they must both have access to the key and keep it confidential to prevent unauthorized access to the message.

Question 2

__________ key encryption schemes are secure if the public key is authenticated.

Accepted Answer

Public key encryption schemes are secure if the public key itself is authenticated. This can be achieved through digital certificates, where a trusted third party verifies the identity of the owner of the public key before issuing the certificate. Without authentication, there is a risk of man-in-the-middle attacks where an attacker could intercept and replace the public key with their own, compromising the security of the encryption. Therefore, it is important to ensure the public key is authenticated to ensure the security of the encryption.

Question 3

Although public announcement of public keys is convenient, anyone can forge a public announcement.

Accepted Answer

Public announcement of public keys can be impersonated or forged by a malicious actor, making it important to verify the authenticity of public keys through methods such as digital signatures or certificate authorities.

Question 4

Because certificates are forgeable they cannot be placed in a directory without the need for the directory to make special efforts to protect them.

Accepted Answer

Certificates, especially those used in digital contexts, are designed to be secure and verifiable through cryptographic means. Directories can store certificates without needing special protection efforts specifically for the certificates themselves, as the security and authenticity of a certificate are ensured through its built-in cryptographic signatures and public key infrastructure (PKI). Verification of a certificate's validity can be performed by anyone with access to the certificate's public key, not just the directory storing it.

Question 5

Frequent key changes are usually desirable to limit the amount of data compromised if an attacker learns the key.

Accepted Answer

Frequent key changes help limit the amount of data that can be decrypted using a compromised key. If an attacker learns a key and it is not changed frequently, they can use it to access a lot of data. However, if keys are changed frequently, the amount of data that can be accessed using a compromised key is limited by the time interval between key changes.

Question 6

Some sort of mechanism or protocol is needed to provide for the secure distribution of keys.

Accepted Answer

This statement is true as secure distribution of keys is crucial for secure communication and requires a protocol that ensures confidentiality and integrity of the keys.

Question 7

_________ implementations make use of X.509 certificates.

Accepted Answer

PKI (Public Key Infrastructure) systems are designed to provide security when transmitting messages over a network. X.509 certificates are a type of cryptographic technology that is commonly used in PKI systems to provide authentication and encryption. Therefore, implementations that make use of X.509 certificates are typically PKI-based solutions.

Question 8

X.509 defines the format for private-key certificates.

Accepted Answer

X.509 defines the format for public-key certificates, not private-key certificates.

Question 9

X.509 is an important standard because the certificate structure and authentication protocols defined in X.509 are used in a variety of contexts.

Accepted Answer

X.509 is widely used for digital certificates in TLS/SSL, VPN, email encryption, code signing, and many other applications.

Question 10

Master keys can be distributed in some noncryptographic way such as physical delivery.

Accepted Answer

Master keys can be delivered physically, for example, through a secure courier service or by hand delivery, without relying on cryptographic protocols.

Question 11

Each user must share a unique key with the key distribution center for purposes of key distribution.

Accepted Answer

In order for the key distribution center to securely distribute keys to each user, each user must have a unique key that is shared only between themselves and the distribution center. This ensures that only authorized users are able to access the encrypted information.

Question 12

The distribution of session keys delays the start of any exchange and places a burden on network capacity.

Accepted Answer

The distribution of session keys requires an additional step in the exchange process, which delays the start of any communication. Furthermore, the distribution of these keys can also put a burden on network capacity, as they must be transmitted securely to all parties involved in the exchange.

Question 13

Key distribution often involves the use of _________ which are generated and distributed for temporary use between two parties.

Accepted Answer

Session keys are unique encryption keys that are generated for temporary use between two parties. They are used for short periods of time and then discarded, making them an ideal choice for secure key distribution. Public key certificates, private key certificates, and master keys are not typically used for temporary key distribution between two parties.

Question 14

The topics of cryptographic key management and cryptographic key distribution are complex,involving cryptographic,protocol, and management considerations.

Accepted Answer

Cryptographic key management and distribution involve complex considerations related to cryptography, protocols, and overall management.

Question 15

For link encryption manual delivery is awkward.

Accepted Answer

The answer of For link encryption manual delivery is awkward....

Question 16

Key distribution often involves the use of __________ which are infrequently used and are long lasting.

Accepted Answer

Master keys are infrequently used and are long-lasting. They are used to generate and distribute the session keys, which are short-lived keys used to encrypt and decrypt actual data exchanged during a session. Private key certificates and public key certificates are used for authentication and not key distribution.

Question 17

A random number would not be a good choice for a nonce.

Accepted Answer

A random number can be easily guessed or recreated, increasing the chances of a successful attack. A better choice for a nonce would be a value that is unique and not easily predictable, such as a timestamp.

Question 18

A public-key certificate scheme alone does not provide the necessary security to authenticate the public key.

Accepted Answer

A public-key certificate scheme includes a third-party certification authority that verifies the identity of the certificate holder, ensuring that the public key belongs to the intended party. This process provides the necessary security to authenticate the public key. Without this verification, there is no guarantee that the public key belongs to a trusted entity.

Question 19

Typically the session key is used for the duration of a logical connection,such as a frame relay connection or transport connection,and then it is permanently stored.

Accepted Answer

The session key is typically used for the duration of a session or communication session, which may consist of multiple connections. Once the session is terminated, the session key is usually discarded and not permanently stored.

Question 20

A __________ defines the procedures needed to revoke digital certificates.

Accepted Answer

Revocation of digital certificates is an important aspect of the Public Key Infrastructure (PKI) and includes procedures for revoking certificates. A PKI is a set of policies, procedures, hardware, software, and people that collectively provide a framework for secure transmission of data using digital certificates. Therefore, D, public key infrastructure, is the best choice as it defines the procedures needed to revoke digital certificates.

Quiz 14: Key Management and Distribution