EC-COUNCIL EC-COUNCIL Certifications 212-81 Questions & Answers

• Question 101:

  Which of the following Secure Hashing Algorithm (SHA) produces a 160-bit digest from a message with a maximum length of (264-1) bits and resembles the MD5 algorithm?

  A. SHA-0

  B. SHA-2

  C. SHA-1

  D. SHA-3

  Correct Answer: C

  SHA-1 https://en.wikipedia.org/wiki/SHA-1 SHA-1 (Secure Hash Algorithm 1) is a cryptographic hash function which takes an input and produces a 160-bit (20-byte) hash value known as a message digest ?typically rendered as a hexadecimal number, 40 digits long. It was designed by the United States National Security Agency, and is a U.S. Federal Information Processing Standard. SHA-1 produces a message digest based on principles similar to those used by Ronald L. Rivest of MIT in the design of the MD2, MD4 and MD5 message digest algorithms, but generates a larger hash value (160 bits vs. 128 bits).

• Question 102:

  3DES can best be classified as which one of the following?

  A. Digital signature

  B. Symmetric algorithm

  C. Asymmetric algorithm

  D. Hashing algorithm

  Correct Answer: B

  Symmetric algorithm

  https://en.wikipedia.org/wiki/Triple_DES

  Triple DES (3DES or TDES), officially the Triple Data Encryption Algorithm (TDEA or Triple DEA), is a symmetric-key block cipher, which applies the DES cipher algorithm three times to each data block. The Data Encryption Standard's (DES)

  56-bit key is no longer considered adequate in the face of modern cryptanalytic techniques and supercomputing power. However, an adapted version of DES, Triple DES (3DES), uses the same algorithm to produce a more secure encryption.

• Question 103:

  A list of certificates that have been revoked.

  A. CA

  B. CRL

  C. PCBC

  D. OCSP

  Correct Answer: B

  CRL https://en.wikipedia.org/wiki/Certificate_revocation_list In cryptography, a certificate revocation list (or CRL) is "a list of digital certificates that have been revoked by the issuing certificate authority (CA) before their scheduled expiration date and should no longer be trusted".

• Question 104:

  A transposition cipher invented 1918 by Fritz Nebel, used a 36 letter alphabet and a modified Polybius square with a single columnar transposition.

  A. ADFVGX Cipher

  B. ROT13 Cipher

  C. Book Ciphers

  D. Cipher Disk

  Correct Answer: A

  ADFVGX Cipher https://en.wikipedia.org/wiki/ADFGVX_cipher ADFGVX cipher was a field cipher used by the German Army on the Western Front during World War I. ADFGVX was in fact an extension of an earlier cipher called ADFGX. Invented by Lieutenant Fritz Nebel (1891?977) and introduced in March 1918, the cipher was a fractionating transposition cipher which combined a modified Polybius square with a single columnar transposition.

• Question 105:

  If the round function is a cryptographically secure pseudorandom function, then ___rounds is sufficient to make it a "strong" pseudorandom permutation.

  A. 15

  B. 16

  C. 3

  D. 4

  Correct Answer: D

  https://en.wikipedia.org/wiki/Feistel_cipher

  Michael Luby and Charles Rackoff analyzed the Feistel cipher construction, and proved that if the round function is a cryptographically secure pseudorandom function, with Ki used as the seed, then 3 rounds are sufficient to make the block

  cipher a pseudorandom permutation, while 4 rounds are sufficient to make it a "strong" pseudorandom permutation (which means that it remains pseudorandom even to an adversary who gets oracle access to its inverse permutation).

  Because of this very important result of Luby and Rackoff, Feistel ciphers are sometimes called Luby-Rackoff block ciphers.

• Question 106:

  John works as a cryptography consultant. He finds that people often misunderstand the reality of breaking a cipher. What is the definition of breaking a cipher?

  A. Finding any method that is more efficient than brute force

  B. Uncovering the algorithm used

  C. Rendering the cypher no longer useable

  D. Decoding the key

  Correct Answer: A

  Finding any method that is more efficient than brute force.

  https://en.wikipedia.org/wiki/Cryptanalysis

  Bruce Schneier notes that even computationally impractical attacks can be considered breaks: "Breaking a cipher simply means finding a weakness in the cipher that can be exploited with a complexity less than brute force. Never mind that

  brute-force might require 2^128 encryptions; an attack requiring 2^110 encryptions would be considered a break...simply put, a break can just be a certificational weakness: evidence that the cipher does not perform as advertised."

• Question 107:

  Part of understanding cryptography is understanding the cryptographic primitives that go into any crypto system. A(n) _______ is a fixed-size input to a cryptographic primitive that is random or pseudorandom.

  A. Key

  B. IV

  C. Chain

  D. Salt

  Correct Answer: A

  Key

  https://en.wikipedia.org/wiki/Key_(cryptography)

  In cryptography, a key is a piece of information (a parameter) that determines the functional output of a cryptographic algorithm. For encryption algorithms, a key specifies the transformation of plaintext into ciphertext, and vice versa for

  decryption algorithms. Keys also specify transformations in other cryptographic algorithms, such as digital signature schemes and message authentication codes.

• Question 108:

  Uses a formula, M_n = 2^n 1 where n is a prime number, to generate primes. Works for 2, 3, 5, 7 but fails on 11 and on many other n values.

  A. Fibonacci Numbers

  B. Co-prime Numbers

  C. Even Numbers

  D. Mersenne Primes

  Correct Answer: D

  Correct answers: Mersenne Primes https://en.wikipedia.org/wiki/Mersenne_prime Mersenne prime is a prime number that is one less than a power of two. That is, it is a prime number of the form M_n = 2^n 1 for some integer n. They are named after Marin Mersenne, a French Minim friar, who studied them in the early 17th century. If n is a composite number then so is 2^n 1. Therefore, an equivalent definition of the Mersenne primes is that they are the prime numbers of the form M_p = 2^p 1 for some prime p.

• Question 109:

  Bob's password is hashed, and so is John's. Even though they used different passwords, the hash is the same. What is this called?

  A. A collision

  B. A mistake

  C. Convergence

  D. Transposition

  Correct Answer: A

  A collision

  https://en.wikipedia.org/wiki/Collision_(computer_science) A collision or clash is a situation that occurs when two distinct pieces of data have the same hash value, checksum, fingerprint, or cryptographic digest.

• Question 110:

  Numbers that have no factors in common with another.

  A. Fibonacci Numbers

  B. Even Numbers

  C. Co-prime numbers

  D. Mersenne Primes

  Correct Answer: C

  Correct answers: Co-prime numbers https://en.wikipedia.org/wiki/Coprime_integers Two integers a and b are said to be relatively prime, mutually prime, or coprime if the only positive integer (factor) that evenly divides both of them is 1. Consequently, any prime number that divides one of a or b does not divide the other. This is equivalent to their greatest common divisor (gcd) being 1. The numerator and denominator of a reduced fraction are coprime. The numbers 14 and 25 are coprime, since 1 is their only common divisor. On the other hand, 14 and 21 are not coprime, because they are both divisible by 7.