Cryptographic data integrity algorithms

Question 1

what are Hash functions?

Answer 1

Functions that accepts a variable length block of data and produces a fixed size hash value

Question 2

Are hash values public or private?

Answer 2

public

Question 3

What do hash functions detect?

Answer 3

changes to message

Question 4

Give to cryptographic hash function properties and define each.

Answer 4

1- One-Way property : computationally infeasible to find data mapping to a specific hash value
2- Collision-free property : computationally infeasible to find two data to same hash

Question 5

What are the applications of Cryptographic hash functions?

Answer 5

• Message authentication
• digital signatures
• one way password file
• intrusion detection and virus detection
• PRF, PRNG

Question 6

What is message authentication>

Answer 6

verify the integrity of the message

Question 7

What is digital signature?

Answer 7

the hash value of a message is encrypted using the user’s private key

Question 8

What is one way password file?

Answer 8

keeping the hash value of the password not the actual password

Question 9

what is intrusion and virus detection

Answer 9

Keep and check hash files on the system

Question 10

h=H(x), we say that x is a ….. of h, and x is a data block whose hash function is —. the function is —

Answer 10

preimage,h,H

Question 11

Collision is:
a. one to one hash mapping
b. one to many hash mapping
c. many to one hash mapping
d. many to many hash mapping

Answer 11

c

Question 12

State the hash function requirements.

Answer 12

• variable input size
• fixed output size
• efficiency: H(x) is easy to compute for any given ‘x’ making SW and HW implementations practical.
• preimage resistant(one way property): for given ‘h’ it is infeasible to find y in H(y) = h
• second preimage resistant(weak collision resistant) : for given block x, it is infeasible to find y!x in H(x) = H(y)
• Collision resistant(strong): it is infeasible to find a pair(x,y) such that H(y) = H(x)
  pseudo-randomness : Output of H meets standard tests for pseudo-randomness

Question 13

State attacks on Hash Functions

Answer 13

• Brute force
• cryptanalysis
• preimage and secon preimage: find y in H(y) such that H(y) = h
• collision resistance : determine two values with the same hash value(x and y) such the H(x)=H(y)

Question 14

what determines the length of the hash code against brute force?

Answer 14

2^m/2

Question 15

True or False:
128 bits is inadequate , 160 bits suspect

Answer 15

True

Question 16

MD4 produces a ….. bit hash value

Answer 16

160

Question 17

SHA-1 is considered :
a. secure
b. not secure

Answer 17

b

Question 18

versions of SHA (also known as SHA-2) are:

Answer 18

SHA-256
SHA-384
SHA-512

Question 19

What are message security requirements?

Answer 19

-Disclosure
-Source repudiation
-destination repudiation
-Traffic analysis
-Masquerade
-content modification
- sequence modification
-timing modification

Question 20

what is the type that is based on a hash function

Answer 20

keyed hash functions as MAC

Question 21

True or False:
Hash functions are slower than MACs

Answer 21

False, Hash function are faster than MACs

Question 22

In key hashed functions , what does a hash include?

Answer 22

A key

Question 22

Give the Original Proposal of key-hashed functions as Mac.

Answer 22

KeyHashed = Hash(Key|Message)

Question 23

The security of MACs can be an advantage in which type of attack?

Answer 23

Brute Force, and MACs work as MAC pairs

Question 24

What does MAC use encryption for?and does it use the same keys

Answer 24

Secrecy, No, it uses separate keys for each.

Question 24

What are the requirements for MAC?

Answer 24

MAC needs to satisfy the following: - Knowing a message and MAC is infeasible to find another message with the same MAC - MAC should be distributed uniformly - MAC should depend equally on all bits in a message

Question 24

State MAC properties.

Answer 24

- MAC is a cryptographic checksum - it has an input data of variable length - it has a fixed sized authenticator(Output) - it uses a secret key K - MAC is many-to-one function meaning that many messages can have the same MAC, but finding these needs to be very difficult.

Question 25

MAC is a cryptographic .....

Answer 25

Checksum MAC = CK(M)

Question 26

Why do we use MAC?

Answer 26

For Authentication

Question 27

True or False: MAC is a Digital Signature

Answer 27

False

Question 28

What is the fixed sized block of data from MAC generated from?

Answer 28

a message and a secret key MAC = C(K, M)

Question 29

What does a MAC create?

Answer 29

A fixed sized block

Question 30

How does the receiver make sure that the message is not altered?

Answer 30

By performing a certain computation on the message and checks if it matches the MAC

Question 30

True or False: In MAC, Encryption need not to be reversible.

Answer 30

True

Question 31

When can public Key Encryption be efficient?

Answer 31

When the sender signs(signature) their message using their private key, and encrypts it using the public key of the receiver. this assures secrecy and authentication

Question 31

MAC is appended to a message as a.....

Answer 31

Signature

Question 32

Allows for easy replicability of embedded Hash functions

Answer 32

HMAC

Question 32

What is Symmetric Message Encryption?

Answer 32

- Receiver knows that the sender must have created the message - Only the sender and receiver know the key used - know content cannot be altered - if a message has a suitable structure, redundancy or a checksum to detect and changes.

Question 33

What does HMAC preserve?

Answer 33

the original performance of the hash function without significant degradation .

Question 34

HMAC handles keys in a very difficult way

Answer 34

This statement is False, HMAC handles keys in a simple way

Question 35

Internet Standard of HMAC

Answer 35

RFC2104

Question 36

Write the whole function of HMAC

Answer 36

HMACK(M) = Hash[(K+ XOR opad )|| Hash[(K+ XOR ipad || M)]]

Question 37

In HMAC what is K+?

Answer 37

the key padded to size opad

Question 38

how much is the overhead of HMAC

Answer 38

1

Question 38

what does the security of a HMAC depend on?

Answer 38

the hash algorithm

Question 39

Attacking HMAC requires:

Answer 39

- brute force attack on key used - birthday attack

Question 40

Digital Signatures provide the ability to:

Answer 40

- Verify the author, date and time - Authenticate message contents - Be checked by others to settle disagreements

Question 41

In DSA , how many bits is the signature ? And how many bits is the security?

Answer 41

320 bits 512-1024 Respectively

Question 42

DSA is smaller and faster than RSA

Answer 42

This statement is true

Question 42

In direct digital signature, who is involved?

Answer 42

Sender and Receiver only.

Question 43

Security depends on the sender/receiver's private/public key.

Answer 43

Sender's , private key.