Network and Security (D329)

Correct Answer

A. The key is chosen from very long texts such as a book.

Explanation

The security of the One-Time Pad does not depend on the key being chosen from very long texts such as a book. The key must be truly random, at least as long as the message, and used only once for each encryption. The key can be any truly random string of sufficient length, and it is the randomness, length, and one-time use that provide the encryption's security, not the source from which the key is chosen.

Why other options are wrong

B. The key is at least as long as the message that must be encrypted.

This is a requirement for a secure One-Time Pad. The key must be long enough to cover the entire message, ensuring that each bit of the message is securely encrypted without the need for key reuse.

C. The key is truly random.

This is a fundamental requirement for the One-Time Pad's security. A truly random key ensures that there is no predictability, making it impossible for attackers to analyze the ciphertext and break the encryption.

D. Each key is used only once.

This is another critical requirement for the One-Time Pad. Reusing keys creates patterns that can be exploited by attackers, making the encryption vulnerable. The key must be discarded after each use to maintain perfect security.

Correct Answer

B. To act as a centralized authentication system.

Explanation

Kerberos is a network authentication protocol designed to provide secure authentication over an insecure network. It uses a trusted third party (Key Distribution Center, KDC) to authenticate users and services within the network, ensuring that the right parties are communicating with each other securely.

Why other options are wrong

A. To provide public-key encryption for secure communication

Kerberos does not primarily use public-key encryption. It relies on symmetric-key encryption to authenticate users and services. Public-key encryption is typically used in other protocols like SSL/TLS.

C. To manage network routing and traffic

Kerberos does not handle network routing or traffic management. Its sole focus is on authentication and ensuring that only authorized users can access services.

D. To protect against malware attacks

While Kerberos can enhance security by authenticating users, it is not designed to specifically protect against malware attacks. Malware protection is typically handled by other security systems such as antivirus software or firewalls.

Correct Answer

B. Digital authentication

Explanation

Digital authentication establishes that a subject attempting to access a digital service is in control of the technologies used to authenticate and ensures that the correct entity is attempting access. It provides the assurance that the person or system using the technology is authorized and legitimate. Authentication is crucial in digital services to ensure proper access control.

Why other options are wrong

A. Identity proofing

Identity proofing refers to the process of verifying the identity of a subject before they can be authenticated. While important, it is more about verifying the identity before authentication rather than ensuring control over the technologies used for authentication.

C. X.509 Certificate

An X.509 certificate is a standard for public key infrastructure (PKI) that is used for encrypting communication or verifying the identity of a subject. However, it does not directly establish control over the technologies used for authentication itself.

D. Digital identity

Digital identity refers to the representation of a subject's identity in digital form. While it relates to identity verification, it does not specifically address the technologies used to authenticate and ensure control over access to a digital service.

Correct Answer

A. Authenticator

Explanation

In the Kerberos authentication protocol, the Authenticator helps mitigate replay attacks by ensuring that authentication requests are fresh and not reused by an attacker. An authenticator includes a timestamp that proves the request is recent, and the Kerberos system uses it to verify the request's validity. By including time-sensitive data in each authentication, the authenticator prevents attackers from capturing and reusing previous valid authentication messages to impersonate users.

Why other options are wrong

B. Key Distribution Center

This is incorrect because while the Key Distribution Center (KDC) plays a vital role in Kerberos by issuing tickets, it is not directly responsible for preventing replay attacks. The KDC facilitates the authentication process, but it is the authenticator that helps mitigate replay attacks by incorporating time-sensitive elements.

C. Asymmetric cryptography

This is incorrect because Kerberos relies on symmetric encryption, not asymmetric encryption, for authentication. While asymmetric cryptography is crucial for other applications, it is not the mechanism Kerberos uses to prevent replay attacks.

D. Realms

This is incorrect because realms define the administrative boundaries within Kerberos authentication, but they are not specifically designed to prevent replay attacks. Realms group users and services under the same administrative domain, but they do not provide a direct mechanism to prevent the reuse of authentication messages.

Correct Answer

D. To produce a fixed-size output (hash value) from variable-sized input

Explanation

A hash function in cryptography takes an input of any size and produces a fixed-size string of characters, which is typically a digest that uniquely represents the input data. This is useful for ensuring data integrity, as any change in the input will result in a drastically different hash value.

Why other options are wrong

A. To encrypt and decrypt messages

Hash functions do not perform encryption or decryption. They are one-way functions, meaning once data is hashed, it cannot be reversed to retrieve the original input.

B. To generate random keys

Hash functions are not used for generating random keys. Key generation usually involves random number generators or key derivation functions specifically designed for that purpose.

C. To compress data

While hash functions reduce input size to a fixed output, they are not data compression tools. Compression aims to reduce the size of data for storage or transmission, while hashing is used for verification and integrity.

Correct Answer

B. To issue digital certificates that authenticate the identity of users

Explanation

The primary function of a Certificate Authority (CA) within a Public Key Infrastructure (PKI) is to issue and manage digital certificates. These certificates authenticate the identity of users, devices, or services and link public keys to their respective entities. The CA ensures trust in the certificates it issues, making it a cornerstone of secure communication.

Why other options are wrong

A. To generate encryption keys for users

While the CA may assist in the key management process, it does not typically generate encryption keys for users. Users generate their own keys, which the CA then certifies.

C. To store all user data securely

The CA does not store all user data. It mainly manages certificates and related public key infrastructure tasks. User data is stored in databases or systems outside the CA.

D. To provide end-user support for cryptographic software

The CA does not provide direct end-user support for cryptographic software. Its role is focused on managing and issuing certificates, while user support is handled by other entities, like the software vendor or a helpdesk.

Correct Answer

B. To securely store cryptographic keys and detect unauthorized access attempts

Explanation

A tamper-proof device, often referred to as a Hardware Security Module (HSM), is designed to securely store cryptographic keys and prevent unauthorized access. It provides physical and logical protections against tampering, ensuring that keys remain secure and that any attempts to access or modify the keys are detected.

Why other options are wrong

A. To enhance the speed of encryption processes

The primary purpose of a tamper-proof device is not to speed up encryption but to securely store keys. While such devices may indirectly support encryption processes, their main function is security, not performance.

C. To provide a user-friendly interface for key management

Tamper-proof devices are typically not focused on user interfaces. Instead, their purpose is to provide secure key storage and detection of tampering, often in a more secure, non-interactive manner. User interfaces are usually separate from the core functions of these devices.

D. To replace the need for encryption algorithms

Tamper-proof devices do not replace encryption algorithms; they simply enhance security by securely storing keys and managing access. Encryption algorithms are still essential for the encryption and decryption of data, with the tamper-proof device only safeguarding the cryptographic keys.

Correct Answer

A. To issue and manage digital certificates

Explanation

A Certificate Authority (CA) is a critical component of Public Key Infrastructure (PKI). The primary role of a CA is to issue, manage, and revoke digital certificates, which are used to verify the identity of users, devices, or services within a network. These certificates are essential for establishing trust in encrypted communications and digital signatures. By authenticating the public key associated with a digital certificate, the CA helps ensure secure communications and verifies the identity of the entities involved.

Why other options are wrong

B. To encrypt data using symmetric keys

This option is incorrect because the role of the CA is not to perform encryption using symmetric keys. While encryption is essential in PKI, it is performed using the public and private keys associated with digital certificates, not symmetric keys that are managed by a CA.

C. To generate random cryptographic keys

Although key generation is essential to cryptography, it is not the main function of the CA. The CA's primary task is to issue and manage certificates, not to generate cryptographic keys. Key generation is usually done by the entity that owns the certificate, such as the user or device.

D. To monitor network traffic for security breaches

Monitoring network traffic for security breaches is typically done by intrusion detection systems (IDS) or security information and event management (SIEM) systems, not by the CA. The CA's focus is on certification and identity verification rather than monitoring network traffic.

Correct Answer

B. By signing the certificate with its private key

Explanation

A Certificate Authority (CA) validates the authenticity of a digital certificate by signing it with its own private key. This signature acts as a guarantee that the certificate has been issued by a trusted CA, and it proves that the identity and public key contained in the certificate have been verified by the CA. Anyone who has the CA's public key can verify this signature, thus ensuring the certificate's authenticity.

Why other options are wrong

A. By encrypting the certificate with the user's public key

The certificate is not encrypted with the user's public key. Instead, it is signed by the CA's private key, allowing anyone with the CA's public key to verify its authenticity. The encryption with the user's public key would be irrelevant to the CA's role in validating the certificate.

C. By issuing the certificate without any verification

Issuing certificates without verification would defeat the purpose of having a Certificate Authority. The CA must thoroughly validate the identity and the associated public key before issuing a certificate to ensure its authenticity.

D. By storing the certificate in a public database

Storing the certificate in a public database does not validate its authenticity. The certificate might be publicly available, but validation requires the CA's signature on the certificate, not merely storage.