According to NISTIR 8259A, what supports reliable device inventory?
A Shared topic name
B Common model number
C Public IP address
D Unique logical identifier
Answer: D. Unique logical identifier. NIST’s baseline calls for each IoT device to be uniquely identifiable logically and physically.
Before installing an OTA image, what helps verify its publisher?
A Filename suffix
B Version number
C Checksum only
D Digital signature
Answer: D. Digital signature. A trusted digital signature can verify that software came from an authorized publisher and was not altered.
When unauthorized clients probe network ports, which NIST capability limits access?
A Data protection
B Device identification
C Logical access to interfaces
D Software update
Answer: C. Logical access to interfaces. NIST names logical access to interfaces as a device capability that restricts local and network access to authorized entities.
Under NIST’s baseline, which data does the data-protection capability cover?
A Firmware versions only
B Network interfaces only
C Stored and transmitted data
D Device identities only
Answer: C. Stored and transmitted data. NIST’s data-protection capability covers data stored on the device and data sent over networks.
When a long-lived credential leaks, what response limits future misuse?
A Change device display
B Increase sample rate
C Rename MQTT topic
D Revoke and rotate keys
Answer: D. Revoke and rotate keys. Revoking the exposed credential and issuing a replacement prevents continued use of the compromised key.
Old actuator commands must not be accepted again. Which defense detects replay?
A Larger payload
B Nonce or counter
C Public topic
D Longer timeout
Answer: B. Nonce or counter. Fresh nonces or sequence counters help a receiver recognize stale or repeated commands.
QoS 1 may redeliver an MQTT message. How can consumers avoid duplicate side effects?
A Idempotent processing
B Longer polling
C More retries
D Wider topic
Answer: A. Idempotent processing. Idempotent processing makes repeating the same operation safe, which matters with at-least-once delivery.
What delivery guarantee does MQTT QoS 2 specify?
A Best effort
B Exactly once
C At least once
D At most once
Answer: B. Exactly once. QoS 2 uses a handshake to provide exactly-once delivery at the MQTT protocol level.
For CoAP over UDP, which security protocol does RFC 7252 describe?
A SMTP
B FTP
C DTLS
D SSH
Answer: C. DTLS. RFC 7252 describes securing CoAP over UDP with Datagram Transport Layer Security.
Which approach can provide network credentials during secure enrollment?
A Anonymous multicast
B Shared default secret
C Open Wi-Fi scanning
D Trusted onboarding
Answer: D. Trusted onboarding. NIST’s trusted onboarding process can provide network credentials in a controlled manner and maintain device security through its lifecycle.
Cloud connectivity fails during a process. Where should a safety interlock execute?
A Local controller
B Remote dashboard
C Public broker
D Email client
Answer: A. Local controller. A safety interlock should not depend on a remote cloud round trip when immediate local action is required.
Before retiring a connected sensor, what should happen to its credentials?
A Reuse fleet-wide
B Publish them publicly
C Store in topic
D Revoke credentials
Answer: D. Revoke credentials. Revoking credentials at decommissioning prevents a retired device from retaining access.
To contain one compromised device, how should broker topics be authorized?
A Device-specific permissions
B One shared account
C Anonymous publish
D Wildcard access
Answer: A. Device-specific permissions. Least-privilege permissions restrict each device to the topics it needs.
If a certificate binds device identity to a public key, what authenticates that binding?
A Subject name
B CA signature
C Expiration date
D Public key
Answer: B. CA signature. A trusted certificate authority signs the certificate binding its subject identity to a public key.
Intermediaries must not decrypt CoAP payloads. Which object-security method fits?
A OSCORE
B SMTP
C NAT
D DHCP
Answer: A. OSCORE. OSCORE protects CoAP message objects end to end, so an intermediary need not terminate transport security to read the payload.
What can NIST cybersecurity state awareness let a device report?
A Security state
B Room temperature
C Battery chemistry
D User preference
Answer: A. Security state. NIST includes the capability to report device cybersecurity state to authorized entities.
Which startup control checks software before it runs?
A Sensor polling
B Clock sync
C Topic discovery
D Secure boot
Answer: D. Secure boot. Secure boot verifies the device’s boot software against a trusted chain before execution.
To limit privacy exposure, what should an IoT application collect?
A All nearby devices
B Continuous audio
C Necessary data only
D Every available field
Answer: C. Necessary data only. Data minimization limits collection to information needed for the system’s purpose.
Why assign a distinct cryptographic key to each device?
A Increase packet size
B Simplify passwords
C Isolate device compromise
D Share firmware faster
Answer: C. Isolate device compromise. Per-device keys limit the impact of one exposed credential and support individual revocation.
Separate IoT and corporate networks help limit what?
A Clock drift
B Sensor noise
C Packet loss
D Lateral movement
Answer: D. Lateral movement. Network segmentation can contain a compromised device and restrict movement into other network zones.
Identical default passwords across a fleet create what main risk?
A Sensor drift
B Fleet-wide compromise
C Radio congestion
D Clock skew
Answer: B. Fleet-wide compromise. An attacker who discovers one shared default credential may be able to access many devices.
Enclosure opening can be detected by which component?
A Current meter
B Tamper switch
C Light sensor
D Temperature probe
Answer: B. Tamper switch. A tamper switch can detect physical opening and trigger an alert.
During an OTA write failure, what design aids recovery?
A Open debug port
B Unverified image
C Known-good firmware slot
D Shared password
Answer: C. Known-good firmware slot. A recovery slot holding known-good firmware can restore operation after a failed update.
How should MQTT over TCP protect traffic in transit?
A DTLS only
B TLS
C ICMP
D FTP
Answer: B. TLS. MQTT commonly uses TLS over TCP to authenticate peers and protect data in transit.
Restricting a gateway to its own measurements requires which rule?
A Allow its own topic
B Use public wildcard
C Allow every topic
D Disable authentication
Answer: A. Allow its own topic. Restricting the gateway to its own topic enforces least privilege and limits the effect of compromise.