Cryptography final
in the diffie hellman algorithm, the condition for selecting the value of α
(Ans: α being a primitive root of q)
In RSA, Ф(n) = _______ in terms of p and q.
(p-1)(q-1)
the number of s-boxes in AES
1
what is 13 mod 6 and -13 mod 6?
1 and 5
in SHA-512, the message is divided into blocks of size _____ bits for the hash computation
1024
calculate the GCD of 1160718174 and 316258250 using Euclidean algorithm
1160718174 = 3(316258250) + 211943424 316258250 = 211943424 + 104314826 211943424 =2(104314826) + 3313772 104314826 = 31(3313772) + 1587894 3313772 =2(1587894 )+ 137984 1587894 =11(137984 )+ 70,070 137984 = 70070 + 67914 70070 = 67914 + 2156 67914 =31( 2156) + 1078 2156 =2(1078 )+ 0
how many rounds does the AES-192 perform?
12
AES uses a _______ bit block size
128
SHA-1 produces a hash value of
160 bits
6. ø(19)
18
the defense against timing attacks on RSA includes
Blinding and Random delay
what is the encryption algorithm for Vigenere cipher?
Ci = (pi + ki) mod 26
For p = 11 and q = 5 and choose e=19. Apply RSA algorithm where message=3 and find the cipher text.
c = 37
what is the decryption algorithm for vernam cipher?
ci = pi⊕ki where pi = ith binary digit of plaintext ki = ith binary digit of key ci = ith binary digit of ciphertext
the hash function is
collision free
The defense against timing attacks on RSA includes
constant exponentiation time, random delay, and blinding
Conversion of cypher text to plaintext is
decryption
the information known to a cryptanalyst is known plaintext attack is
encryption algorithm cipher text one or more plaintext-cyphertext pairs formed with secrete key.
AES follows Fiestel structure
false
Diffie Hellman Algorithm can be used for authentication.
false
Elliptic key cryptography is a private key cryptography.
false
In RSA, we select a value 'e' such that it lies between 0 and Ф(n) and it is relatively prime to Ф(n).
false
RSA problem is defined as
finding eth roots modulo a composite n: recovering a value m such that C≡me(mod n), where(n,e)is an RSA public key and C is an RSA cipher text)
write Eulers theorem
for every a and n that are relatively prime: aø(n) 1(mod n) i.e. for any a,n where gcd(a,n)=1
the condition for the relatively prime numbers is
gcd of two numbers is 1
the full form of HMAC is
hash based message authentication code
write Fermats theorem
if p is prime and a is a positive integer not divisible by p then a^(p-1) = 1 (mod p)
The condition for "a" to be primitive root of "p"
is if a is a primitive root of the prime number p, then the numbers • a mod p,a 2 mod p, ...., a p-1 mod p are distinct and consist of the integers from 1 through p - 1 in some permutation.
Cryptology
is the study of cryptanalysis and cryptography
Euler's totient function
is written as ø(n), is defined as the number of positive integers less than n and relatively prime to n
the requirements for digital signature function includes
it must be relatively easy to produce the signature it must be relatively easy to recognize and verify the digital signature it must be computationally infeasible to forge the signature
Advantages of ECC includes________________
less memory smaller key size faster computations
MAC is a
many-to-one mapping
when a hash function is used to provide message authentication, the hash function value is referred to as
message digest
digital signatures guarantees
no alterations messages during transit authenticate message contents at the time of signature verifies author, date, and time signature
the application hash function included _________
one-way password file intrusion detection virus detection
In the RSA algorithm, two random large values 'p' and 'q'are selected. Which of the following is the property of 'p' and 'q'?
p and q should be prime
the defense against mathematical attacks on RSA include
p and q should differ in length by only a few digits both (p-1) and (q-1) should contain a large prime factor gce(p-1,q-1) should be small
Given two primes 3 and 7, use RSA to encrypt a message 4.
p=3 q=7 n=21 Ф(n)=2*6=12 let e=5 5*d mod 12=1 c= 45(mod 21)=16
In the Diffie Hellman algorithm, the condition for selecting the value of q
prime number
in Diffie-Hellman, the condition for selecting private key if global parameters are q and α
private key xA < q
Which is the largest disadvantage of the symmetric Encryption?
problem of secure transmission of the secrete key
differentiate between public key and private key
public key can be shared with everyone where as the private key must be kept secrete in order to keep the message secure. In Public key cryptography, both the public and the private keys can be used to encrypt/decrypt the message; but the corresponding key from the one used to encrypt is used to decrypt it.
the leftmost 4 bits in s-box represents the following value
row
the digital signature provides authentication to
sender and message
in "known message attack" type, the attacker has the following information
set of messages and their signatures
the requirements for hash function include
variable input fixed output one way function collision free strong collision free
The equation for calculating public key in Diffie Hellman is
yA = α ^xA mod q
the general equation used to represent elliptic curves in ECC is
y^2 = x^3 + a.x +b
Eulers totient function
ø(p) = p-1
the meaning of cryptanalytic attacks on MAC is ___________
trying to exploit some property of the algorithm
Find gcd(1970,1066) using Euclidean algorithm.
1970 = 1 x 1066 + 904 1066 = 1 x 904 + 162 904 = 5 x 162 + 94 162 = 1 x 94 + 68 94 = 1 x 68 + 26 68 = 2 x 26 + 16 26 = 1 x 16 + 10 16 = 1 x 10 + 6 10 = 1 x 6 + 4 6 = 1 x 4 + 2 4 = 2 x 2 + 0
3^201 mod 11 =
3 3201 mod 11 = (310) 20 * 31 mod 11 = 3
the number of stages in each round of AES includes
4
For p = 23 and q = 2 and choose d=3 . Apply RSA algorithm where Cipher message=2 and thus find the plain text.
8
what is the number of rounds computation steps in the SHA-512 algorithm
80
CIA Triad
Confidentiality, Integrity, Availability
another name for MAC is
Cryptographic checksum
What are elliptic curves? Why are Elliptic Curves used in the cryptography?
Elliptic curves are the curves which follow the equation y2 = x3 + a.x + b and used in the cryptography. Elliptic curves provide equivalent security for smaller key size they are used in cryptography. Also elliptic curves are faster and needs less computations. Elliptic curves require less memory. Because of the above advantages, elliptic curves are used in cryptography.
Which of the following types of cryptography should be used when minimal overhead is necessary for a mobile device?
Elliptical curve cryptography
the difference between MAC and HMAC is
HMAc algorithm is a specified type of MAC algorithm that uses a hash algorithm internally to generate MAC
Explain Euler's theorem with an example
It is a generalisation of Fermat's Theorem and states that for every a and n that are relatively prime: aø(n) 1(mod n) i.e. for any a,n where gcd(a,n)=1
what is RC4 algorithm? explain the process of encryption and decryption
It is a symmetric key encryption algorithm invented by Ron Rivest .It uses variable key size and it is a byte-oriented stream cipher .To encrypt, XOR the value k with the next byte of plaintext. Ci = Mi XOR S[k];To decrypt, XOR the value k with the next byte of ciphertext. Mi = Ci XOR S[k];
what are the types of cryptographic hash functions
MD5, SHA, RIPEMD, whirlpool
MAC stands for
Message authentication code
protection agains denial by one of the entities involved in a communication (origin, destination)is called a:
Non-Repudation
define the RSA problem
RSA problem is defined as the task of taking eth roots modulo a composite n: recovering a value m such that C ≡ me (mod n), where (n, e) is an RSA public key and C is an RSA ciphertext
the passive attack type is:
Release of message contents
AES algorithm is derived by
Rijndael
Give an example for Diffie Hellman Algorithm.
Sender & Receiver agree on prime q=353 and α=3, let xA=97, yA = α xA mod q=397 mod 353 = 40 . let xB=233 , yB= α xB mod q=3233 mod 353 = 248 KAB= yBxA mod q = 24897 mod 353= 160 ; KAB= yAxB mod q = 40233 mod 353= 160 160 is the shared key.
MACs are also called
Tags
give an example for play fair cipher
The keyword is MONARCHY Message = Move forward Plaintext = mo ve fo rw ar dx mo -> ON; ve -> UF; fo -> PH, etc Ciphertext = ON UF PH NZ RM BZ
what is the difference between mono alphabetic and poly alphabetic cipher
The monoalphabetic cipher is a permutation of a finite set of elements S is an ordered sequence of all the elements of S, with each element appearing exactly once. In mono- the relationship between cipher text and plain text is one to one. The polyalphabetic cipher improves on this by using different monoalphabetic substitutions as one proceeds through the plaintext. The polyalphabetic cipher is more complex. In a poly- one letter of plain text can be mapped to many letters of cipher text.
an intelligent threat is called
an attack, a deliberate attempt to evade security services and violate the security policy of a system.
explain the brute force attack on MAC
attack the key space and attack the MAC value
man in the middle attack can endanger security of Diffie-Hellman method if two parties are not ________
authenticated
the application of digital signature algorithm includes
authentication
The requirements for selecting random numbers in cryptography is
statistically random, uniform distribution, independent, unpredictability of future values from previous values.
the method of Caesar cipher is
substitution
the stages defined in AES encryption are
substitution bytes shift rows mixed columns and add round key
the security of Diffie-Hellman key exchange relies on which assumption?
that it is computationally infeasible to solve the discrete log problem
The meaning of brute force attack on hashing is
the adversary will try to find a value y such that h(x) = y
When a cryptographic construction provides message authenticity, what does the receiver learn
the authentication of sender and message integrity
.Why is Diffie-Hellman susceptible to man-in-the-middle attacks? Name one way to prevent such attacks?
the diffie-hellman key exchange protocol is vulnerable to man in the middle attacks because it does not authenticate the participants. this can be overcome with the use of digital signatures and public-key certificates
what is the rail fence transposition technique?
the message is written in a rectangle, row by row, and read the message off, column by column, but permute the order of the column, the order of the columns then becomes the key to the algorithm.
the number of subways in key expansion is
the number of rounds +1
in "key only attack" the attacker knows only __________
the senders public key
According to x.800 the architecture of security is
the three aspects of information security a) security attack b) security mechanism (control) c) security service
explain the brute force attack on RSA cryptosystems
this involves trying all possible private keys (d)
what is the objective of Diffie-Hellman key exchange?
to establish a shared secrete key on both sides
cryptanalysis is used
to find some insecurity in a cryptography scheme
The use of Pseudorandom Number generator is
to generate random numbers
AES is faster then 3DES
true
GCD(a,b) is the same as GCD(| a |, | b |)
true
In RSA, the values of 'e' lies between 1 and Ф(n).
true
MAC is not a digital signature
true
RC4 is a byte-oriented stream cipher.
true
digital signature algorithm makes use of secure hash algorithm
true
in hash function output length is fixed
true
incase of hashing, a collision occurs if we have x is not equal to y and H(x) = H(y)
true
