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

EC-COUNCIL 212-81 Online Questions & Answers

• Question 151:

  Represents the total number of possible values of keys in a cryptographic algorithm or other security measure, such as a password.

  A. Key Schedule
  B. Key Clustering
  C. Key Space
  D. Key Exchange
  C. Key Space

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  Explanation

  Key Space https://en.wikipedia.org/wiki/Key_space_(cryptography) Algorithm's key space refers to the set of all possible permutations of a key. To prevent an adversary from using a brute-force attack to find the key used to encrypt a message, the key space is usually designed to be large enough to make such a search infeasible. On average, half the key space must be searched to find the solution. Another desirable attribute is that the key must be selected truly randomly from all possible key permutations. Should this not be the case, and the attacker is able to determine some factor that may influence how the key was selected, the search space (and hence also the search time) can be significantly reduced. Humans do not select passwords randomly, therefore attackers frequently try a dictionary attack before a brute force attack, as this approach can often produce the correct answer in far less time than a systematic brute force search of all possible character combinations.

• Question 152:

  The greatest weakness with symmetric algorithms is _____.

  A. They are less secure than asymmetric
  B. The problem of key exchange
  C. The problem of generating keys
  D. They are slower than asymmetric
  B. The problem of key exchange

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  Explanation

  The problem of key exchange https://en.wikipedia.org/wiki/Symmetric-key_algorithm Symmetric-key algorithms are algorithms for cryptography that use the same cryptographic keys for both encryption of plaintext and decryption of ciphertext. The keys may be identical or there may be a simple transformation to go between the two keys. The keys, in practice, represent a shared secret between two or more parties that can be used to maintain a private information link. This requirement that both parties have access to the secret key is one of the main drawbacks of symmetric key encryption, in comparison to public-key encryption (also known as asymmetric key encryption).

• Question 153:

  What size block does AES work on?

  A. 64
  B. 128
  C. 192
  D. 256
  B. 128

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  Explanation

  https://en.wikipedia.org/wiki/Advanced_Encryption_Standard Rijndael is a family of ciphers with different key and block sizes. For AES, NIST selected three members of the Rijndael family, each with a block size of 128 bits, but three different key lengths: 128, 192 and 256 bits.

• Question 154:

  A linear congruential generator is an example of what?

  A. A coprime generator
  B. A prime number generator
  C. A pseudo random number generator
  D. A random number generator
  C. A pseudo random number generator

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  Explanation

  A pseudo random number generator https://en.wikipedia.org/wiki/Linear_congruential_generator A linear congruential generator (LCG) is an algorithm that yields a sequence of pseudo- randomized numbers calculated with a discontinuous piecewise linear equation. The method represents one of the oldest and best-known pseudorandom number generator algorithms. The theory behind them is relatively easy to understand, and they are easily implemented and fast, especially on computer hardware which can provide modular arithmetic by storage-bit truncation.

• Question 155:

  Ciphers that write message letters out diagonally over a number of rows then read off cipher row by row. Also called zig-zag cipher.

  A. Rail Fence Cipher
  B. Null Cipher
  C. Vigenere Cipher
  D. ROT-13
  A. Rail Fence Cipher

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  Explanation

  Rail Fence Cipher https://en.wikipedia.org/wiki/Rail_fence_cipher The rail fence cipher (also called a zigzag cipher) is a form of transposition cipher. It derives its name from the way in which it is encoded.

• Question 156:

  Created in 1977 by Ron Rivest, Adi Shamir, and Leonard Adleman at MIT. Most widely used public key cryptography algorithm. Based on relationships with prime numbers. This algorithm is secure because it is difficult to factor a large integer composed of two or more large prime factors.

  A. PKI
  B. DES
  C. RSA
  D. Diffie-Helmann
  C. RSA

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  Explanation

  RSA

  https://en.wikipedia.org/wiki/RSA_(cryptosystem)

  RSA (Rivest璖hamir瑼dleman) is a public-key cryptosystem that is widely used for secure data transmission. It is also one of the oldest. The acronym RSA comes from the surnames of Ron Rivest, Adi Shamir, and Leonard Adleman, who

  publicly described the algorithm in 1977. An equivalent system was developed secretly, in 1973 at GCHQ (the British signals intelligence agency), by the English mathematician Clifford Cocks. That system was declassified in 1997.

• Question 157:

  An attack that is particularly successful against block ciphers based on substitution- permutation networks. For a block size b, holds b-k bits constant and runs the other k through all 2k possibilities. For k=1, this is just deferential cryptanalysis, but with k>1 it is a new technique.

  A. Differential Cryptanalysis
  B. Linear Cryptanalysis
  C. Chosen Plaintext Attack
  D. Integral Cryptanalysis
  D. Integral Cryptanalysis

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  Explanation

  Integral Cryptanalysis https://en.wikipedia.org/wiki/Integral_cryptanalysis Integral cryptanalysis is a cryptanalytic attack that is particularly applicable to block ciphers based on substitution-permutation networks. It was originally designed by Lars Knudsen as a dedicated attack against Square, so it is commonly known as the Square attack. It was also extended to a few other ciphers related to Square: CRYPTON, Rijndael, and SHARK. Stefan Lucks generalized the attack to what he called a saturation attack and used it to attack Twofish, which is not at all similar to Square, having a radically different Feistel network structure. Forms of integral cryptanalysis have since been applied to a variety of ciphers, including Hierocrypt, IDEA, Camellia, Skipjack, MISTY1, MISTY2, SAFER++, KHAZAD, and FOX (now called IDEA NXT).

• Question 158:

  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
  A. Key

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  Explanation

  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 159:

  Which of the following is a block cipher?

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

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  Explanation

  AES https://en.wikipedia.org/wiki/Advanced_Encryption_Standard AES is a subset of the Rijndael block cipher developed by two Belgian cryptographers, Vincent Rijmen and Joan Daemen, who submitted a proposal to NIST during the AES selection process

• Question 160:

  Which one of the following best describes a process that splits the block of plaintext into two separate blocks, then applies the round function to one half, and finally swaps the two halves?

  A. Block ciphers
  B. Symmetric cryptography
  C. Feistel cipher
  D. Substitution cipher
  C. Feistel cipher

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  Explanation

  Correct answer: https://en.wikipedia.org/wiki/Feistel_cipher Feistel cipher (also known as Luby璕ackoff block cipher) is a symmetric structure used in the construction of block ciphers, named after the German-born physicist and cryptographer Horst Feistel who did pioneering research while working for IBM (USA); it is also commonly known as a Feistel network. A large proportion of block ciphers use the scheme, including the US Data Encryption Standard, the Soviet-developed GOST and the more recent Blowfish and Twofish ciphers. In a Feistel cipher, encryption and decryption are very similar operations, and both consist of iteratively running a function called a "round function" a fixed number of times.