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CS432: Network Security > Cryptographic data integrity algorithms > Flashcards

Cryptographic data integrity algorithms Flashcards

1
Q

what are Hash functions?

A

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

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2
Q

Are hash values public or private?

A

public

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3
Q

What do hash functions detect?

A

changes to message

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4
Q

Give to cryptographic hash function properties and define each.

A

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

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5
Q

What are the applications of Cryptographic hash functions?

A
  • Message authentication
  • digital signatures
  • one way password file
  • intrusion detection and virus detection
  • PRF, PRNG
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6
Q

What is message authentication>

A

verify the integrity of the message

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7
Q

What is digital signature?

A

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

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8
Q

What is one way password file?

A

keeping the hash value of the password not the actual password

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9
Q

what is intrusion and virus detection

A

Keep and check hash files on the system

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10
Q

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

A

preimage,h,H

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11
Q

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

A

c

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12
Q

State the hash function requirements.

A
  • 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
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13
Q

State attacks on Hash Functions

A
  • 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)
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14
Q

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

A

2^m/2

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15
Q

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

A

True

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16
Q

MD4 produces a ….. bit hash value

A

160

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17
Q

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

A

b

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18
Q

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

A

SHA-256
SHA-384
SHA-512

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19
Q

What are message security requirements?

A

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

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20
Q

what is the type that is based on a hash function

A

keyed hash functions as MAC

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21
Q

True or False:
Hash functions are slower than MACs

A

False, Hash function are faster than MACs

22
Q

In key hashed functions , what does a hash include?

A

A key

22
Q

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

A

KeyHashed = Hash(Key|Message)

23
Q

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

A

Brute Force, and MACs work as MAC pairs

24
Q

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

A

Secrecy, No, it uses separate keys for each.

24
Q

What are the requirements for MAC?

A

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

24
Q

State MAC properties.

A
  • 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.
25
Q

MAC is a cryptographic …..

A

Checksum
MAC = CK(M)

26
Q

Why do we use MAC?

A

For Authentication

27
Q

True or False:
MAC is a Digital Signature

A

False

28
Q

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

A

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

29
Q

What does a MAC create?

A

A fixed sized block

30
Q

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

A

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

30
Q

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

A

True

31
Q

When can public Key Encryption be efficient?

A

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

31
Q

MAC is appended to a message as a…..

A

Signature

32
Q

Allows for easy replicability of embedded Hash functions

A

HMAC

32
Q

What is Symmetric Message Encryption?

A
  • 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.
33
Q

What does HMAC preserve?

A

the original performance of the hash function without significant degradation .

34
Q

HMAC handles keys in a very difficult way

A

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

35
Q

Internet Standard of HMAC

A

RFC2104

36
Q

Write the whole function of HMAC

A

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

37
Q

In HMAC what is K+?

A

the key padded to size opad

38
Q

how much is the overhead of HMAC

A

1

38
Q

what does the security of a HMAC depend on?

A

the hash algorithm

39
Q

Attacking HMAC requires:

A
  • brute force attack on key used
  • birthday attack
40
Q

Digital Signatures provide the ability to:

A
  • Verify the author, date and time
  • Authenticate message contents
  • Be checked by others to settle disagreements
41
Q

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

A

320 bits
512-1024
Respectively

42
Q

DSA is smaller and faster than RSA

A

This statement is true

42
Q

In direct digital signature, who is involved?

A

Sender and Receiver only.

43
Q

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

A

Sender’s , private key.

44
Q
A

CS432: Network Security (1 decks)

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