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The CORRECT OPTION is (a) replacing each digit by 9 minus that digit

Explanation: Nine’s COMPLEMENT of a number is FORMED by replacing each digit by 9 minus that digit.

Right option is (B) x

To EXPLAIN I would SAY: Complement of Complement of number GIVES the same number.

The correct option is (a) Shift cipher

Easiest explanation: Shift cipher is a mono-alphabetic cipher in which each letter of the plaintext is substituted by another letter to form the ciphertext. It is the simplest form of substitution cipher SCHEME WHEREIN the concept is to replace each alphabet by another alphabet which is ‘shifted’ by some fixed number between 0 and 25. In this scheme, both sender and receiver AGREE on a secret shift number for shifting the alphabet and this number lies between 0 and 25 becomes the key to the encryption. Occasionally, Caesar cipher is used to describe the Shift cipher when the ‘shift of three’ is used.

The correct option is (a) 64 BITS

For explanation: Blowfish symmetric block cipher was CREATED after DES but before AES. Its block size is 64 bits, and it can use key lengths from 32 up to 448 bits. It is a 16-round Feistel cipher and unlike in DES it’s S-boxes are key-dependent and so they are GENERATED dynamically.

The CORRECT choice is (b) Symmetric block cipher

To elaborate: AES encryption USES symmetric block ciphers to encrypt the messages. It is at least 6 times FASTER than 3 DES. AES uses a substitution-permutation network and this network is a series of operations that either replaces input with output bits (substitution) or shuffles the bits (permutation). It uses 128-bit input PLAINTEXT and it operates on bytes rather than bits. Here, the input is represented as 16 bytes (because 128 bits = 16 bytes) and is arranged in a 4 x 4 MATRIX.

Right choice is (a) expansion, mixing, substitution, permutation

Easy explanation: The Feistel function which occurs in EVERY block has 3 steps

i) Expansion:- The incoming 32-bit block has half of its bits duplicated, making it a 48-bit block.

ii) Mixing:- The new, 48-bit input block is PUT through an XOR gate with this round’s unique subkey.

iii) Substitution:- The MIXED, 48-bit block is divided into 8 6-bit pieces. Each of these 8 pieces is put through an S-block which will output only 4-bits using non-linear-transformation. Permutation: The 32 output bits are then arranged in a SPECIFIC permutation that ensures that they will be distributed among different S-blocks in the NEXT round. This is the most important part of security in DES and it helps to avoid simple, algebra-based attacks.

The correct answer is (b) 56, 8

Easy explanation: DES is a symmetric system that uses BLOCK ciphers which CONSIST of 56 random BITS, and 8 more bits are used for error detection. First the data is sent into the system and then divided into two 32-bit blocks. Those two blocks are sent through the entire system using criss-cross which is known as the Feistel system. There are 16 LAYERS in DES. At each layer, one half of the data passes through the Fiestel function and after its completion, it is XORd with the other half of the data. Each layer has its own subkey which is DERIVED from the main 56-bit key by using a key scheduler.

Right option is (a) STREAM cipher

Best explanation: The stream cipher is the one-time pad that uses the XOR function on the plaintext with a pseudo-RANDOM sequence. The input plaintext is encrypted one byte at a time incrementally. As the random sequence is not possible, a pseudo-random sequence is USED. These pseudo-random sequence are the outputs of a generator given an INITIAL SEED which is a number used to initialize a pseudo-random number generator.

Correct answer is (a) 160 bits

The best EXPLANATION: The Secure Hash Algorithm or SHAis based on MD4 encryption SYSTEM. This algorithm gives an output of a LONGER 160-bit message that is why it is harder to construct ANOTHER message that yields the same resultant message.

The correct option is (b) RSA ENCRYPTION

The best I can explain: The asymmetric ciphers use asymmetric ALGORITHMS that use one key to ENCRYPT data and a different key to decrypt ciphers. These algorithms are USED in RSA encryption and public-key cryptography in which the public key is used to encrypt data and the private key is used to decrypt data.

Correct choice is (a) permutation

Easiest explanation: In CRYPTOGRAPHY, a method of encryption where the positions of plaintext held by units are shifted according to a REGULAR SYSTEM so that the CIPHERTEXT constructs a permutation of the plaintext is TERMED as transposition cipher.

Correct CHOICE is (c) 2211

For explanation: Since every two employee have their own secret key ENCRYPTION and decryption. Both USERS have to agree on a secret key to communicate USING symmetric cryptography. After that, each message is ENCRYPTED with that key it is transmitted and decrypted with the same key. Here, key distribution must be secret. For n = 67 we would need\(\frac{n(n-1)}{2} = \frac{67(67-1)}{2}\) = 2211 keys.

Right ANSWER is (d) 60

The explanation: Given PLAIN text (m) = 7, P = 5, Q = 16, where P and Q are two prime integer

n = P * Q ⇒ n = 5*16 = 80 ⇒ Z = (P-1)*(Q-1) ⇒ Z = (5-1)*(16-1) = 4*15 = 60.

The correct choice is (B) 3772

To ELABORATE: Given that n=3901 and e=31. We know that n = p∗q where p and q are PRIME numbers, which gives 3901 = 47*83. Now, ϕ(n) is EULER’s totient function i.e., ϕ(n) = (p−1)∗(q−1)

ϕ(n) = (47−1)∗(83−1)

ϕ(n) = 46*82 = 3772.

Right answer is (b) bijective function

Best EXPLANATION: We have a mathematical NOTION that a bijective function can be used on the characters’ POSITIONS to ENCRYPT a message and an inverse function is used to decrypt the message.

The CORRECT answer is (B) 60

For explanation: GIVEN n = 77, that means P and q must be 7 and 11 that is they must be co-prime to each other. Now we know that ϕ(n) = (p – 1) (q – 1)

ϕ(n) = (7 – 1) (11 – 1)

ϕ(n) = 6*10

ϕ(n) = 60.

Right choice is (a) SSL VISIBILITY appliances

To explain: In the data loss prevention SYSTEMS, Web proxies and antivirus network security functions, SSL visibility appliances DECRYPT traffic to make it AVAILABLE for all networks.

The correct choice is (a) 13

The BEST explanation: The ROT13 CAESAR cipher system has an offset of 13 and it is one of the comprehensive cipher scheme. However, the Vigenere cipher employs Caesar cipher as one ELEMENT of the encryption process.

Right option is (a) 13969, 13680

Easy EXPLANATION: We know that, Z = P1*p2 = 229*61 = 13969 and Φ = (p1 – 1)(p2 – 1) = (229 – 1)(61 – 1) = 228*60 = 13680.

Right option is (b) 128 BITS

For explanation: The RC6 Feistel block CIPHER is a 20-round cipher scheme which includes a fixed block SIZE of 128 bits and it supports 128, 192, and 256-bit keys for ENCRYPTION of messages.

Correct option is (C) Unicode technique

Best EXPLANATION: BASE64 and hex encoding scheme encode characters(or only bytes). First, we need to encode the characters as bytes and after that encode the bytes. In TERMS of compactness and simplicity, the best technique is Unicode scheme.

Correct option is (c) 770190.04

The best explanation: It is known that to GET original MESSAGE m after decrypting we can have the formulam=c1/e. In this case: (456,871,122,391,882,538)^1/3 = 770190.04 and this is the REQUIRED answer.

The correct ANSWER is (c) feistel STRUCTURE

The explanation: The Feistel structure system TEA OPERATES on two 32-bit unsigned integer numbers. It uses a 128-bit key that can be USED to BUILD a simple key schedule by mixing all of the key elements.

Right choice is (b) 2^74

To elaborate: If there are 2^56 cipher TEXTS per plain text and a total of 2^18 plaintexts of length 18 EXISTS which will all decrypt to the same plaintext, and this HOLDS for EVERY plaintext. There are a total of 2^56plaintexts of length 56. Now, there must be 2^56. 2^18 = 2^74 distinct ciphertexts which all decrypt to plaintexts of length 56. If all those ciphertexts are the same length, they must be at least 74 bits long.

The correct answer is (a) 1024 BITS

For explanation: In CRYPTOGRAPHY system, the value of z in x ≡ z^e (MOD m) should be at least 1024 bits.

The correct OPTION is (C) 6

Easiest explanation: According to CONGRUENCE relation, 56 ≡ 6 (mod 24), because 56 − 32 = 24, which is a multiple of 24. So, the remainder is 6.

The CORRECT option is (d) O(g)

For explanation I would say: The modular EXPONENTIATION completely depends on the operating SYSTEM environment and the PROCESSOR for its performance. The above said method REQUIRES a time complexity of O(g) for its completion.

Correct answer is (a) p1x = 0 for all x in F

To elaborate: A field can be DEFINED as an ALGEBRAIC structure in which multiplication, ADDITION, subtraction, and division are well-defined and satisfy similar PROPERTIES. If there is a unique PRIME number p1 then a finite field F has the property of p1x = 0, for all x in F and this prime number is called the characteristics of the field.

The correct choice is (a) Diffie-HEllman KEY exchange

Explanation: Exponentiation in the finite fields has its MANY applications in the public key CRYPTOGRAPHY system. Now, the Diffie–Hellman key exchange can have the concept that exponentiation is COMPUTATIONALLY inexpensive in the finite fields and the discrete logarithm which is the inverse of exponentiation, can be computationally EXPENSIVE.

The correct answer is (b) Classical modular exponentiation algorithm

The best I can explain: To MULTIPLY m and N, they are CONVERTED to Montgomery form: mR mod X and nR mod X. When multiplied, these produce mnR^2 mod X, and the Montgomery reduction produces abR mod N which is the Montgomery form of the desired product. After that, the low bits are DISCARDED which gives a result less than 2X. One final subtraction reduces this to less than X. Hence, this procedure can have a better computational complexity than standard division algorithms.

The correct choice is (a) integer exponents

Explanation: Exponentiation with integer exponents is termed in any multiplicative MONOID. Exponentiation is described INDUCTIVELY by 1) h^0 = 1 for all h ∈ S, h^n+1 = h^n h and non-negative INTEGERS n, If n is a negative integer then h^n is only defined if h has an inverse in S. Monoids define many STRUCTURES including GROUPS and rings (under multiplication).

The CORRECT choice is (a) GCD(53,21) = 1

Easy EXPLANATION: The MULTIPLICATIVE inverse of “a modulo m” can be found out by extended Euler’s GCD algorithm, and the time complexity of this method is O(LOGM). We know that the multiplicative inverse of “x modulo n” exists if and only if x and n are relatively PRIME (i.e., if gcd(a, m) = 1). So, in this case GCD(53,21) = 1.

Correct option is (d) 41.42

For EXPLANATION: LCM(41 * 42, 42 * 42) = 41.42.42.41 / 41.42 = 41.42.

The CORRECT CHOICE is (b) 1

The EXPLANATION is: gcd(0, 5) = 0^min(1, 0).5^min(0, 1).

Correct ANSWER is (d) 3^5

To explain: GCD(a, b) = 3^min(13, 5).5^min(17, 0).2^min(12, 0).

Right OPTION is (b) 35

Explanation: 35 = 5.7 which is the PRODUCT of TWO prime NUMBERS.