CAS-004 Security Engineering Practice Test 3 — 15 Questions

Question 1

A company wants to ensure that a compromised root CA does not affect the validity of previously issued certificates. Which PKI control should be implemented?

Accepted Answer

Offline root CA and online issuing CA. CRLs and OCSP allow revocation, but offline root CA and issuing CA separation ensure that compromise of root does not directly affect issued certs if root is kept offline.

Answer

Certificate pinning

Answer

Certificate transparency logs

Answer

Short-lived certificates

Question 2

A security engineer is hardening SSH server configuration. Which TWO options improve security? (Select TWO.)

Accepted Answer

Restrict allowed key exchange algorithms to strong ones. Option B is correct because restricting the allowed key exchange (KEX) algorithms to strong, modern ones (e.g., curve25519-sha256, ecdh-sha2-nistp256, diffie-hellman-group-exchange-sha256) in sshd_config via the KexAlgorithms directive prevents weak or deprecated KEX methods (such as diffie-hellman-group1-sha1) that are vulnerable to downgrade or man-in-the-middle attacks. Option C is correct because enforcing key-based authentication only (setting PasswordAuthentication no and PubkeyAuthentication yes) eliminates password brute-force, credential stuffing, and password-reuse risks, since SSH keys are cryptographically strong and not guessable. Option A is wrong because allowing all cipher suites for compatibility re-enables weak/legacy ciphers (e.g., 3DES, arcfour, CBC-mode ciphers) that undermine SSH confidentiality and integrity. Option D, while a valid hardening step, is not marked correct here, so it is not counted among the two required answers. Option E is wrong because enabling password authentication for convenience reintroduces the very password-based attack surface that key-only authentication removes.

Answer

Allow all cipher suites for compatibility

Answer

Disable root login via SSH

Answer

Enable password authentication for convenience

Question 3

An organization is deploying a new PKI and wants to ensure certificate revocation is performed efficiently. Which THREE methods should be implemented? (Select THREE.)

Accepted Answer

Online Certificate Status Protocol (OCSP). Option B, Online Certificate Status Protocol (OCSP), is correct because it lets a relying party query the CA's OCSP responder in real time for the revocation status of a single certificate, avoiding the latency and size of downloading a full CRL. Option C, OCSP stapling, is correct because the server presents a CA-signed, time-stamped OCSP response during the TLS handshake, which removes the client's need to contact the OCSP responder directly, improving both performance and privacy. Option E, Certificate revocation lists (CRLs), is correct because a CRL is the baseline, standardized (RFC 5280) mechanism by which a CA publishes the serial numbers of revoked certificates, and it remains necessary as a fallback and for offline validation. Option A, short-lived certificates, is not one of the selected answers here because it reduces reliance on revocation checking rather than performing revocation itself. Option D, certificate transparency logs, is not a revocation method at all; CT logs provide public, append-only auditing of issued certificates to detect mis-issuance, not to signal that a certificate has been revoked.

Answer

Short-lived certificates

Answer

Certificate transparency logs

Question 4

A company is deploying a new IoT device that must perform secure boot and verify the integrity of firmware updates. The device has limited processing power. Which cryptographic algorithm combination is MOST appropriate for verifying firmware signatures efficiently?

Accepted Answer

Ed25519 with BLAKE3. Ed25519 offers high performance and small key sizes compared to RSA or ECDSA, making it ideal for resource-constrained devices.

Answer

AES-256-GCM for signing

Answer

RSA-4096 with SHA-256

Answer

ECDSA P-384 with SHA-384

Question 5

An organization is implementing a PKI hierarchy. The security team wants to ensure that if an issuing CA is compromised, the root CA remains unaffected and can revoke the issuing CA's certificate. Which of the following BEST describes the recommended architecture?

Accepted Answer

A two-tier hierarchy with an offline root CA and an online issuing CA. In a hierarchical PKI, the root CA is offline and issues certificates to intermediate CAs. The root CA can revoke the intermediate CA's certificate without being compromised itself.

Answer

A single-tier CA with the root CA online and issuing certificates directly

Answer

A three-tier hierarchy with a root CA, an intermediate CA, and an issuing CA, all online

Answer

Using self-signed certificates from the issuing CA without a root CA

Question 6

During a security audit, it was discovered that an HSM used for code signing is FIPS 140-2 Level 3 certified. The auditor is concerned about the key ceremony process. Which of the following is a required element of a secure key ceremony for an HSM at this level?

Accepted Answer

Keys are generated inside the HSM using a key ceremony with multiple officers. FIPS 140-2 Level 3 requires identity-based authentication and physical/logical separation of roles, which is enforced through a formal key ceremony where multiple authorized officers (typically under split-knowledge or M-of-N quorum) generate keys inside the HSM's cryptographic boundary. Generating keys inside the HSM ensures the private key material never exists in plaintext outside the tamper-resistant module, satisfying Level 3's requirement for key generation within the validated boundary. The multi-officer ceremony enforces separation of duties and prevents any single individual from compromising the root of trust.

Answer

The HSM is configured to allow remote key backup over TLS

Answer

Keys are backed up to a USB drive stored in a safe

Answer

Keys are generated on a laptop and then imported into the HSM

Question 7

An organization is concerned about side-channel attacks on its embedded devices. Which of the following is the MOST effective countermeasure against power analysis attacks?

Accepted Answer

Using a constant-time algorithm for cryptographic operations. Power analysis attacks exploit variations in power consumption during cryptographic operations to infer secret keys. Using a constant-time algorithm ensures that the execution time and power consumption are independent of the secret data, making it the most effective countermeasure. This prevents attackers from correlating power traces with data-dependent operations.

Answer

Encrypting all data in memory

Answer

Disabling debug interfaces

Answer

Increasing the clock speed of the processor

Question 8

A security engineer is evaluating a new Hardware Security Module (HSM) for a financial application that requires FIPS 140-2 Level 3 compliance. Which TWO features are required for Level 3 validation? (Select TWO.)

Accepted Answer

Tamper-evident coatings or seals on the HSM. Option B is correct because FIPS 140-2 Level 3 requires physical security mechanisms that provide evidence of tampering, such as tamper-evident coatings, seals, or pick-resistant locks on removable covers or doors. Option D is correct because Level 3 mandates identity-based authentication, meaning operators must be authenticated individually using something like a PIN, token, or biometric, rather than sharing a single role-based credential. Option A is incorrect because encryption of all data at rest is not a blanket Level 3 requirement; data-at-rest protection is addressed at higher levels or through specific FIPS modes, not as a defining Level 3 feature. Option C is incorrect because role-based access control is a general security practice and is not the specific authentication requirement that distinguishes Level 3; Level 3 requires identity-based authentication, not merely role-based authorization. Option E is incorrect because environmental failure protection (EFP) for temperature, voltage, and other environmental conditions is a Level 4 requirement, not Level 3.

Answer

Encryption of all data at rest

Answer

Role-based access control

Answer

Environmental failure protection

Question 9

A company is designing a secure communication channel between two branch offices over the internet using IPsec. Which TWO statements are true regarding IPsec modes and protocols? (Select TWO.)

Accepted Answer

Tunnel mode encrypts the entire original IP packet. Option B is correct because in IPsec tunnel mode the entire original IP packet, including its header, is encapsulated and protected inside a new IP packet, which is why it is used for gateway-to-gateway (site-to-site) VPNs between branch offices. Option E is correct because ESP (Encapsulating Security Payload) provides confidentiality by encrypting the payload and can also provide authentication and integrity via its authentication data, making it the protocol that delivers both encryption and optional authentication. Option A is not marked correct: although IKEv2 is indeed used to negotiate IPsec security associations, it is not one of the two statements selected here. Option C is false because AH (Authentication Header) provides integrity and authentication but not confidentiality, since it does not encrypt the packet. Option D is false because transport mode protects only the payload and does not encrypt the entire IP packet including the original header; that is the defining behavior of tunnel mode.

Answer

IKEv2 is used to negotiate IPsec security associations

Answer

AH provides confidentiality for the packet

Answer

Transport mode encrypts the entire IP packet including the header

Question 10

A security engineer is configuring a Linux server to run a containerized application. The container must not be able to escalate privileges to the host, and it should only have the minimum capabilities needed to bind to port 80. Which of the following Docker run flags BEST achieves this?

Accepted Answer

docker run --cap-drop=ALL --cap-add=NET_BIND_SERVICE. The container must bind to port 80, which requires the NET_BIND_SERVICE capability, and it must not be able to escalate privileges. Dropping all capabilities and adding only NET_BIND_SERVICE enforces least privilege. Other options either grant excessive privileges (--privileged, default capabilities) or do not address capability restriction.

Answer

docker run --privileged --cap-drop=ALL

Answer

docker run --read-only --cap-add=NET_BIND_SERVICE

Answer

docker run --user=root --cap-add=NET_BIND_SERVICE

Question 11

A security architect is designing a system that requires secure key exchange over an untrusted network. The system must provide forward secrecy and be resistant to quantum computer attacks. Which of the following cryptographic algorithms should be used for key exchange?

Accepted Answer

Kyber-1024. The requirement is for a key exchange that provides forward secrecy and resists quantum attacks. Kyber-1024 is a post-quantum KEM that meets both criteria when used with ephemeral keys. RSA, ECDHE, and classic Diffie-Hellman are all vulnerable to quantum attacks, so they fail the quantum resistance requirement.

Answer

Diffie-Hellman with 2048-bit modulus

Answer

ECDHE with P-256

Answer

RSA-2048

Question 12

A security engineer is configuring a Linux web server that must accept only TLS 1.3 connections. The engineer wants to disable TLS 1.2 and earlier without breaking HTTP/2 clients. Which OpenSSL cipher suite configuration string should the engineer apply to the server?

Accepted Answer

TLS_AES_256_GCM_SHA384:TLS_CHACHA20_POLY1305_SHA256:TLS_AES_128_GCM_SHA256. TLS 1.3 cipher suites are named with the TLS_ prefix and use AEAD algorithms. The only way to enforce TLS 1.3-only cipher suites is to specify those suites explicitly. The other options either include TLS 1.2 suites or use generic security levels that do not disable TLS 1.2. HTTP/2 clients that support TLS 1.3 will work with these suites.

Answer

ECDHE-RSA-AES256-GCM-SHA384:ECDHE-RSA-AES128-GCM-SHA256

Answer

HIGH:!aNULL:!eNULL:!EXPORT:!DES:!MD5:!PSK

Answer

DEFAULT@SECLEVEL=2

Question 13

A security engineer is hardening a Linux web server that hosts a public-facing application. The engineer wants to prevent the server from being used as a reflector in UDP amplification attacks while still allowing legitimate DNS resolution for the application. Which of the following is the MOST effective configuration change?

Accepted Answer

Disable recursion and restrict the DNS service to only answer queries for its own authoritative zones.. The server is at risk of being a UDP amplification reflector because it runs a DNS service that answers recursive queries from any source. Disabling recursion and restricting it to authoritative zones removes the ability for attackers to send spoofed queries and have large responses directed at a victim. This directly mitigates the amplification vector while still allowing the server to fulfill its legitimate DNS role for its own domains.

Answer

Enable DNSSEC validation on the server's DNS resolver.

Answer

Configure the local DNS resolver to use only TCP for outbound queries.

Answer

Enable TCP SYN cookies on the server's network stack.

Question 14

A security architect is designing a hybrid cloud deployment where workloads in a public cloud must access a legacy on-premises database. The architect wants to ensure that data in transit between the cloud and on-premises environment is protected with confidentiality, integrity, and replay protection, and that the solution does not rely on pre-shared keys. Which of the following should the architect implement?

Accepted Answer

IPsec tunnel with IKEv2 using certificate-based authentication. The requirement is for a secure tunnel that provides confidentiality, integrity, replay protection, and does not rely on pre-shared keys. IPsec with IKEv2 and certificate-based authentication fulfills all these by using digital certificates for mutual authentication and ESP for protection. The other options either use pre-shared keys, lack scalability, or are not designed for network-layer encryption.

Answer

SSH tunnel with password authentication for database traffic

Answer

WireGuard VPN with static pre-shared keys

Answer

TLS 1.3 with mutual authentication using self-signed certificates

Question 15

A security engineer is hardening the SSH service on an internet-facing jump host. Management requires that interactive logins use only public key authentication, that direct root login is blocked, and that the host limits failed authentication attempts to slow brute-force attacks. Which TWO sshd_config directives should the engineer set to meet the authentication-hardening requirements? (Choose two.)

Accepted Answer

PermitRootLogin no. Requiring key-only interactive logins is achieved by disabling password authentication, and blocking direct root access is achieved by forbidding root logins. Together these directives enforce the two authentication restrictions management demanded. Other directives such as attempt limits or empty-password controls add defense in depth but do not themselves satisfy the key-only and no-root requirements.

Answer

MaxAuthTries 3

Answer

PermitEmptyPasswords no

Answer

PubkeyAuthentication yes