This set of tough Network Security Questions focuses on “IEEE 802.11i WLAN Security – III”.
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
Explanation: 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
Explanation: 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)?
Explanation: 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?
b) Random Number
Explanation: PRF is the secret key.
5. What is ‘Len’ (desirable number of pseudorandom bits) field in the case of CCMP PTK computation?
Explanation: 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
Explanation: 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
Explanation: 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.
Explanation: 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)
Explanation: The pairwise transient key (PTK) is derived from the Pairwise master Key (PMK).
10. The pairwise transient key (PTK) consists of ______________ keys.
Explanation: 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?
Explanation: SHA-1 is used to derive PMK from the PTK.
Sanfoundry Global Education & Learning Series – Cryptography and Network Security.
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