SSCA Security in SIP 2 — Questions and Answers
Question 1: Which SIP header field carries the Digest authentication credentials from a UAC to a UAS?
- Authorization (Correct answer)
- WWW-Authenticate
- Proxy-Authenticate
- Authentication-Info
Correct answer: Authorization
The Authorization header carries the UAC's Digest credentials in response to a 401 challenge from a UAS.
Question 2: What does the 'nonce' parameter in SIP Digest authentication primarily prevent?
- Replay attacks (Correct answer)
- Man-in-the-middle attacks
- Eavesdropping on media
- DNS spoofing
Correct answer: Replay attacks
The nonce is a server-generated, time-limited random value that prevents replay attacks by making each authentication exchange unique.
Question 3: Which transport protocol provides encryption and integrity protection for SIP signaling?
- TLS (Correct answer)
- UDP
- TCP
- SCTP
Correct answer: TLS
TLS (Transport Layer Security) encrypts and integrity-protects SIP signaling messages in transit.
Question 4: What URI scheme is used to indicate that a SIP connection must be established over TLS?
- sips: (Correct answer)
- sip+tls:
- stls:
- sip-secure:
Correct answer: sips:
The 'sips:' URI scheme mandates that TLS must be used for the entire path to the destination.
Question 5: When a SIP proxy challenges a UAC for authentication, which response code does it return?
- 407 (Correct answer)
- 401
- 403
- 400
Correct answer: 407
A SIP proxy uses 407 Proxy Authentication Required, while a UAS uses 401 Unauthorized to issue authentication challenges.
Question 6: What type of attack involves an attacker sending a large volume of SIP INVITE messages to overwhelm a server?
- INVITE flooding (Correct answer)
- Registration hijacking
- Toll fraud
- SIP eavesdropping
Correct answer: INVITE flooding
INVITE flooding is a denial-of-service attack where an attacker floods a SIP server with INVITE requests to exhaust its resources.
Question 7: Which mechanism in SIP allows a registrar to confirm successful authentication to the UAC after registration?
- Authentication-Info header (Correct answer)
- Authorization header
- WWW-Authenticate header
- Proxy-Authorization header
Correct answer: Authentication-Info header
The Authentication-Info header is sent by the server in a 200 OK to provide mutual authentication confirmation to the UAC.
SSCA Security in SIP 2
Which SIP header field carries the Digest authentication credentials from a UAC to a UAS?