A hash function has the following properties?

Question

3) Because public key cryptography is slow compared to symmetric key cryptography, it is often used to securely agree on a ______________

public key    

cipher

private key   

session key

None of the above

4) Message integrity over a communications channel can be assured (any changes can be detected) by the use of a cryptographic tool called a

parity value

hash function 

checksum

byte sum check

All of the above

None of the above

5) A hash function has the following properties (check all that apply)

it will produce a constant output for messages under 1KB in size        

it is a symmetric key algorithm

given message M, it is computationally infeasible to find message M1 such that their hash functions are the same         

it will produce a fixed length output for an input of arbitrary length

All of the above           

None of the above

Answer 1

3) It is used to agree on a session key.

Public and private keys remain unchanged over many sessions and are

used to agree on the session key.

4) All of the above are used to "assure" integrity of communication.

I put "assure" into quotes because these measures can only reduce

the probability that corruption will not be detected.

The reduced probability can be made very close to 0.

5) The answer "given message M, it is computationally infeasible ..."

is definitely correct, because that is the very purpose of a hash function.

The answer "it is a symmetric key algorithm" is definitely incorrect, because

a hash function may normally map many messages to the same output.

The answer "it will produce a constant output for messages under 1KB in size"

could be a property of some hash functions, but it is not inherent for all hash functions.

A hash function could be designed to "produce a fixed length output for an input of arbitrary length",

but that would not be a good hash function.