Network Security Questions on “IEEE 802.11i WLAN Security”.
1. In CCMP a 128-bit AES Key is used for both integrity and confidentiality. The scheme uses a ___________ bit packet number to construct a nonce to prevent __________ attacks.
a) 48, replay
b) 64, replay
c) 48, transient
d) 64, transient
Answer: a
Clarification: The scheme uses a 48-bit packet number to construct a nonce to prevent replay attacks.
2. HMAC SHA-1 produces a hash of length-
a) 180 bits
b) 240 bits
c) 160 bits
d) 40 bits
Answer: c
Clarification: The hash length and key length in HASH SHA-1 is 160 bits.
3. In the IEEE 802.11i PRF, a nonce is generated by the following expression –
nonce = PRF (Random Number, “InitCounter”, MAC || Time, Len)
What is the value of the ‘Len’ (desirable number of pseudorandom bits)?
a) 64
b) 128
c) 256
d) 512
Answer: c
Clarification: Nonce = PRF (Random Number, “InitCounter”, MAC || Time, Len).
4. Nonce = PRF (Random Number, “InitCounter”, MAC || Time, Len)
What is the Key ‘K’ in the above expression?
a) InitCounter
b) Random Number
c) PRF
d) Time
Answer: c
Clarification: PRF is the secret key.
5. What is ‘Len’ (desirable number of pseudorandom bits) field in the case of CCMP PTK computation?
a) 256
b) 384
c) 568
d) 298
Answer: b
Clarification: The ‘Len’ value in the case of CCMP is 128+128+128 = 384 bits.
6. The message input to the IEEE 802.11 pseudorandom Function consists of 4 items concatenated together. Which of the following option is not a part of this message input –
a) the parameter B
b) a byte with value FF (11111111)
c) the parameter A
d) counter value i
Answer: b
Clarification: The byte concatenated has a value 00h.
7. A __________ is a secret key shared by the AP and a STA and installed in some fashion outside the scope of IEEE 802.11i.
a) pre-shared key
b) pairwise transient key
c) master session key
d) key conformation key
Answer: a
Clarification: A pre-shared key(PSK) is a secret key shared by the AP and a STA and installed in some fashion outside the scope of IEEE 802.11i.
8. The Pairwise master key (PMK) can be derived from either PSK or MSK.
a) True
b) False
Answer: a
Clarification: If a PSK is used then the PSK becomes the PMK; if an MSK is used, then the PMK is derived from the MSK using truncation.
PSK – Pre-shared Key
MSK – Master shared key.
9. The pairwise transient key (PTK) is derived from –
a) Key Confirmation Key (KCK)
b) Temporal Key (TK)
c) Pairwise master Key (PMK)
d) Pre-Shared Key (PSK)
Answer: c
Clarification: The pairwise transient key (PTK) is derived from the Pairwise master Key (PMK).
10. The pairwise transient key (PTK) consists of ______________ keys.
a) 3
b) 4
c) 5
d) 2
Answer: a
Clarification: The pairwise transient key (PTK) consists of three keys, which are KCK KEK and TK.
11. Which Hashing algorithm is used to derive the PTK for PMK?
a) SHA-1
b) SHA-2
c) SHA-3
d) MD-5
Answer: a
Clarification: SHA-1 is used to derive PMK from the PTK.