Question

1. Which of these characters is the bad one in cryptographic scenarios?
   1. Alice.
   2. Bo    
   3. Eve.
   4. Turing.
2. A hash function creates a compressed digest of a message. What is that?
   1. A fixed-length sequence of bits the value of which is based upon the value of the original message.   
   2. An encryption of the original message, similar to that done by AES .
   3. The procedure that creates a message via which a man-in-the middle is executed.
   4. A substitution box used in symmetric cryptography
3. Operating systems will store hashed passwords rather than the originals, and then compare login attempts to the hash. Why is this?
   1. Hashes are computationally efficient.
   2. Different length passwords cannot be compared.
   3. Hashes are one-way functions.
   4. All of the above.
4. What is a digital signature?
   1. A digital scan of a signature in a document.   
   2. An encryption of the original message, similar to that done by AES.
   3. A way to authenticate the identity and contents of a message created by someone/something.
   4. Another term for a messages digest.

Answer 1

Q. Which of these characters is the bad one in cryptographic scenarios?

Ans: c

Because Eve is the name usually used to reffer attacker or intruder in cryptographic scenarios.

Q. A hash function creates a compressed digest of a message. What is that?

Ans: a

A fixed-length sequence of bits the value of which is based upon the value of the original message. Hash function is mathematical function which is one way in nature i.e. It is easy to calcuate hash of the variable length input but it is computionally infeasible to get input back from the hash value.

Q. Operating systems will store hashed passwords rather than the originals, and then compare login attempts to the hash. Why is this?

Ans: c

Hashes are one-way functions. Operating systems store hashed passwords rather than the originals because even in case OS gets compromised attacker can't recover the real passwors as hashes are generated by one way functions. More better technique is to add random number as salt to passwords and the store the hash to avoid dictionary attacks.

Q.  What is a digital signature?

Ans: c

A way to authenticate the identity and contents of a message created by someone/something. Digital signature is generated by first hashing the message first and then encrypting hash with senders private key. Hash autenticates the contents of message while encryption with owners private key and decryption with corresponding public key authticates the identity of owner.