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

EC-COUNCIL 212-81 Online Questions & Answers

• Question 61:

  Which one of the following is a symmetric key system using 64-bit blocks?

  A. DES
  B. PGP
  C. DSA
  D. RSA
  A. DES

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  Explanation

  DES https://en.wikipedia.org/wiki/Data_Encryption_Standard DES is the archetypal block cipher--an algorithm that takes a fixed-length string of plaintext bits and transforms it through a series of complicated operations into another ciphertext bitstring of the same length. In the case of DES, the block size is 64 bits. DES also uses a key to customize the transformation, so that decryption can supposedly only be performed by those who know the particular key used to encrypt. The key ostensibly consists of 64 bits; however, only 56 of these are actually used by the algorithm. Eight bits are used solely for checking parity, and are thereafter discarded. Hence the effective key length is 56 bits.

• Question 62:

  A cryptanalysis success where the attacker deduces the secret key.

  A. Information Deduction
  B. Avalanche effect
  C. Shannon's Entropy
  D. Total Break
  D. Total Break

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  Explanation

  Total Break

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

  The results of cryptanalysis can also vary in usefulness. For example, cryptographer Lars Knudsen (1998) classified various types of attack on block ciphers according to the amount and quality of secret information that was discovered:

  Total break -- the attacker deduces the secret key. Global deduction -- the attacker discovers a functionally equivalent algorithm for encryption and decryption, but without learning the key. Instance (local) deduction -- the attacker discovers

  additional plaintexts (or ciphertexts) not previously known.

  Information deduction -- the attacker gains some Shannon information about plaintexts (or ciphertexts) not previously known.

  Distinguishing algorithm -- the attacker can distinguish the cipher from a random permutation.

• Question 63:

  What type of encryption uses different keys to encrypt and decrypt the message?

  A. Asymmetric
  B. Symmetric
  C. Secure
  D. Private key
  A. Asymmetric

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  Explanation

  Asymmetric https://en.wikipedia.org/wiki/Public-key_cryptography Asymmetric cryptography, is a cryptographic system that uses pairs of keys: public keys, which may be disseminated widely, and private keys, which are known only to the owner. The generation of such keys depends on cryptographic algorithms based on mathematical problems to produce one-way functions. Effective security only requires keeping the private key private; the public key can be openly distributed without compromising security.

• Question 64:

  What size block does FORK256 use?

  A. 64
  B. 512
  C. 256
  D. 128
  B. 512

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  Explanation

  https://en.wikipedia.org/wiki/FORK-256 FORK-256 was introduced at the 2005 NIST Hash workshop and published the following year.[6] FORK-256 uses 512-bit blocks and implements preset constants that change after each repetition. Each block is hashed into a 256-bit block through four branches that divides each 512 block into sixteen 32-bit words that are further encrypted and rearranged

• Question 65:

  Which of the following are valid key sizes for AES (choose three)?

  A. 192
  B. 56
  C. 256
  D. 128
  E. 512
  F. 64
  A. 192
  C. 256
  D. 128

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  Explanation

  Correct answers: 128, 192, 256 https://en.wikipedia.org/wiki/Advanced_Encryption_Standard The Advanced Encryption Standard (AES), also known by its original name Rijndael, is a specification for the encryption of electronic data established by the U.S. National Institute of Standards and Technology (NIST) in 2001. 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. 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 66:

  Juanita has been assigned the task of selecting email encryption for the staff of the insurance company she works for. The various employees often use diverse email clients. Which of the following methods is available as an add-in for most email clients?

  A. Caesar cipher
  B. RSA
  C. PGP
  D. DES
  C. PGP

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  Explanation

  PGP https://en.wikipedia.org/wiki/Pretty_Good_Privacy Pretty Good Privacy (PGP) is an encryption program that provides cryptographic privacy and authentication for data communication. PGP is used for signing, encrypting, and decrypting texts, e-mails, files, directories, and whole disk partitions and to increase the security of e-mail communications. Phil Zimmermann developed PGP in 1991.

• Question 67:

  Early attempt to make substitution ciphers more robust, masks letter frequencies, plain text letters map to multiple cipher text symbols.

  A. Scytale Cipher
  B. Playfair Cipher
  C. Homophonic Substitution
  D. ADFVGX Cipher
  C. Homophonic Substitution

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  Explanation

  Homophonic Substitution https://en.wikipedia.org/wiki/Substitution_cipher#Homophonic_substitution An early attempt to increase the difficulty of frequency analysis attacks on substitution ciphers was to disguise plaintext letter frequencies by homophony. In these ciphers, plaintext letters map to more than one ciphertext symbol. Usually, the highest-frequency plaintext symbols are given more equivalents than lower frequency letters. In this way, the frequency distribution is flattened, making analysis more difficult.

• Question 68:

  How did the ATBASH cipher work?

  A. By substituting each letter for the letter from the opposite end of the alphabet (i.e. A becomes Z, B becomes Y, etc.)
  B. By rotating text a given number of spaces
  C. By Multi alphabet substitution
  D. By shifting each letter a certain number of spaces
  A. By substituting each letter for the letter from the opposite end of the alphabet (i.e. A becomes Z, B becomes Y, etc.)

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  Explanation

  By substituting each letter for the letter from the opposite end of the alphabet (i.e. A becomes Z, B becomes Y, etc.)

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

  The Atbash cipher is a particular type of monoalphabetic cipher formed by taking the alphabet (or abjad, syllabary, etc.) and mapping it to its reverse, so that the first letter becomes the last letter, the second letter becomes the second to last

  letter, and so on.

• Question 69:

  Basic information theory is the basis for modern symmetric ciphers. Understanding the terminology of information theory is, therefore, important. Changes to one character in the plaintext affect multiple characters in the ciphertext. What is this referred to?

  A. Avalanche
  B. Confusion
  C. Scrambling
  D. Diffusion
  D. Diffusion

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  Explanation

  Diffusion https://en.wikipedia.org/wiki/Confusion_and_diffusion Diffusion means that if we change a single bit of the plaintext, then (statistically) half of the bits in the ciphertext should change, and similarly, if we change one bit of the ciphertext, then approximately one half of the plaintext bits should change. Since a bit can have only two states, when they are all re-evaluated and changed from one seemingly random position to another, half of the bits will have changed state. The idea of diffusion is to hide the relationship between the ciphertext and the plain text. This will make it hard for an attacker who tries to find out the plain text and it increases the redundancy of plain text by spreading it across the rows and columns; it is achieved through transposition of algorithm and it is used by block ciphers only

• Question 70:

  Which of the following techniques is used (other than brute force) to attempt to derive a key?

  A. Cryptography
  B. Cryptoanalysis
  C. Password cracking
  D. Hacking
  B. Cryptoanalysis

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  Explanation

  Cryptoanalysis https://en.wikipedia.org/wiki/Cryptanalysis Cryptanalysis is the study of analyzing information systems in order to study the hidden aspects of the systems. Cryptanalysis is used to breach cryptographic security systems and gain access to the contents of encrypted messages, even if the cryptographic key is unknown.