EC-COUNCIL 212-81 Online Practice Questions and Exam Preparation

EC-COUNCIL 212-81 Online Questions & Answers

• Question 141:

  The next number is derived from adding together the prior two numbers (1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89).

  A. Odd numbers
  B. Fibonacci Sequence
  C. Fermat pseudoprime
  D. Prime numbers
  B. Fibonacci Sequence

  ---

  Explanation

  Fibonacci Sequence

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

  In mathematics, the Fibonacci numbers, commonly denoted Fn, form a sequence, called the Fibonacci sequence, such that each number is the sum of the two preceding ones, starting from 0 and 1. That is,

  F0 = 0, F1=1, Fn = Fn-1 + Fn-2; for n > 1. The beginning of the sequence is thus:

  0,1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144...

• Question 142:

  The concept that if one bit of data changes, the cipher text will all completely change as well.

  A. Avalanche
  B. Substitution
  C. Confusion
  D. Collision
  A. Avalanche

  ---

  Explanation

  Avalanche https://en.wikipedia.org/wiki/Avalanche_effect In cryptography, the avalanche effect is the desirable property of cryptographic algorithms, typically block ciphers and cryptographic hash functions, wherein if an input is changed slightly (for example, flipping a single bit), the output changes significantly (e.g., half the output bits flip). In the case of high-quality block ciphers, such a small change in either the key or the plaintext should cause a drastic change in the ciphertext. The actual term was first used by Horst Feistel, although the concept dates back to at least Shannon's diffusion.

• Question 143:

  What is an IV?

  A. Random bits added to a hash
  B. The key used for a cryptography algorith
  C. A fixed size random stream that is added to a block cipher to increase randomeness
  D. The cipher used
  C. A fixed size random stream that is added to a block cipher to increase randomeness

  ---

  Explanation

  A fixed size random stream that is added to a block cipher to increase randomeness https://en.wikipedia.org/wiki/Block_cipher_mode_of_operation#Initialization_vector_(IV) An initialization vector (IV) or starting variable (SV) is a block of bits that is used by several modes to randomize the encryption and hence to produce distinct ciphertexts even if the same plaintext is encrypted multiple times, without the need for a slower re-keying process.

• Question 144:

  If the round function is a cryptographically secure pseudorandom function, then ___________ rounds is sufficient to make the block cipher a pseudorandom permutation.

  A. 2
  B. 15
  C. 16
  D. 3
  D. 3

  ---

  Explanation

  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璕ackoff block ciphers.

• Question 145:

  In steganography, ________ is the data to be covertly communicated (in other words, it is the message you wish to hide).

  A. Carrier
  B. Signal
  C. Payload
  D. Channel
  C. Payload

  ---

  Explanation

  Payload https://en.wikipedia.org/wiki/Steganography The payload is the data covertly communicated. The carrier is the signal, stream, or data file that hides the payload, which differs from the channel, which typically means the type of input, such as a JPEG image. The resulting signal, stream, or data file with the encoded payload is sometimes called the package, stego file, or covert message. The proportion of bytes, samples, or other signal elements modified to encode the payload is called the encoding density and is typically expressed as a number between 0 and 1.

• Question 146:

  Which one of the following is an algorithm that uses variable length key from 1 to 256 bytes, which constitutes a state table that is used for subsequent generation of pseudorandom bytes and then a pseudorandom string of bits, which is XORed with the plaintext to produce the ciphertext?

  A. PIKE
  B. Twofish
  C. RC4
  D. Blowfish
  C. RC4

  ---

  Explanation

  RC4 https://en.wikipedia.org/wiki/RC4 RC4 (Rivest Cipher 4 also known as ARC4 or ARCFOUR meaning Alleged RC4, see below) is a stream cipher. While it is remarkable for its simplicity and speed in software, multiple vulnerabilities have been discovered in RC4, rendering it insecure. It is especially vulnerable when the beginning of the output keystream is not discarded, or when nonrandom or related keys are used. Particularly problematic uses of RC4 have led to very insecure protocols such as WEP. The key-scheduling algorithm is used to initialize the permutation in the array "S". "keylength" is defined as the number of bytes in the key and can be in the range 1 keylength 256, typically between 5 and 16, corresponding to a key length of 40 ?128 bits. First, the array "S" is initialized to the identity permutation. S is then processed for 256 iterations in a similar way to the main PRGA, but also mixes in bytes of the key at the same time.

• Question 147:

  Which algorithm was U. S. Patent 5,231,668, filed on july 26, 1991, attributed to David W. Kravitz, and adopted by the U. S. government in 1993 with FIPS 186?

  A. DSA
  B. AES
  C. RC4
  D. RSA
  A. DSA

  ---

  Explanation

  DSA https://en.wikipedia.org/wiki/Digital_Signature_Algorithm DSA is covered by U.S. Patent 5,231,668 , filed July 26, 1991 and now expired, and attributed to David W. Kravitz, a former NSA employee. This patent was given to "The United States of America as represented by the Secretary of Commerce, Washington, D.C.", and NIST has made this patent available worldwide royalty-free. Claus P. Schnorr claims that his U.S. Patent 4,995,082 (also now expired) covered DSA; this claim is disputed.

• Question 148:

  What is a TGS?

  A. The server that escrows keys
  B. A protocol for encryption
  C. A protocol for key exchange
  D. The server that grants Kerberos tickets
  D. The server that grants Kerberos tickets

  ---

  Explanation

  The server that grants Kerberos tickets https://en.wikipedia.org/wiki/Kerberos_(protocol) The client authenticates itself to the Authentication Server (AS) which forwards the username to a key distribution center (KDC). The KDC issues a ticket-granting ticket (TGT), which is time stamped and encrypts it using the ticket-granting service's (TGS) secret key and returns the encrypted result to the user's workstation. This is done infrequently, typically at user logon; the TGT expires at some point although it may be transparently renewed by the user's session manager while they are logged in.

• Question 149:

  Which of the following uses an 80 bit key on 64 bit blocks?

  A. Skipjack
  B. Twofish
  C. DES
  D. AES
  A. Skipjack

  ---

  Explanation

  Skipjack

  https://en.wikipedia.org/wiki/Skipjack_(cipher)

  Skipjack uses an 80-bit key to encrypt or decrypt 64-bit data blocks. It is an unbalanced Feistel network with 32 rounds.

• Question 150:

  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
  D. Mersenne Primes

  ---

  Explanation

  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.