Which of the following is true and if its false why? (a) SHA-2 refers to SHA-256

Question

Which of the following is true and if its false why?

(a) SHA-2 refers to SHA-256.
(b) The number “512” in SHA-512 refers to the length of the hash input.
(c) For 128-bit key AES encryption engine, each of the 10 rounds are exactly the same: each round consists of the four operations of SubBytes, ShiftRows, MixColumns and AddRoundKey.
(d) DES and AES are both secure so they are alternative to each other.
(e) Hash functions could be used to compute HMAC. In the HMAC construction, usually the key and the message are directly concatenated to be hashed, i.e., HMAC = Hash(Key | Message) where ‘|’ is the concatenation operation.

Explanation / Answer

(a) False. SHA2 is a set of Hash Functions. It consists of 6 has functions with hash values 224, 256, 384 and 512 bits. SHA256 is the hash function with hash value 256 bits.

(b)False. SHA512 take input upto a length of 2128 bits and produces a Message Digest as an output which is of 512 bits.

(c) False. Final 10th round of 128 bit AES encryption does not have the MixColumns operation and only has the other 3 operations, namely  SubBytes, ShiftRows and AddRoundKey.

(d) False. DES is not secure as AES. This is because DES has a short key of 56 bit length while AES's strength lies in the strong key of 128, 192 or 256 bits.

(e) In HMAC, the message is sent alongwith hash and a person with secret key can hash the message himself, and if the key is authentic, the resulting and computed hash will match. So probably this one is also false.

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