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

• Question 161:

  What advantage do symmetric algorithms have over asymmetric algorithms

  A. It is easier to implement them in software

  B. They are more secure

  C. They are faster

  D. It is easier to exchange keys

  Correct Answer: C

  They are faster

  Symmetric key encryption is much faster than asymmetric key encryption, because both the sender and the recipient of a message to use the same secret key.

• Question 162:

  With Electronic codebook (ECB) what happens:

  A. The message is divided into blocks and each block is encrypted separately. This is the most basic mode for symmetric encryption

  B. The cipher text from the current round is XORed with the plaintext from the previous round

  C. The block cipher is turned into a stream cipher

  D. The cipher text from the current round is XORed with the plaintext for the next round

  Correct Answer: A

  The message is divided into blocks and each block is encrypted separately. This is the most basic mode for symmetric encryption

  https://en.wikipedia.org/wiki/Block_cipher_mode_of_operation#Electronic_codebook_(ECB )

  The simplest of the encryption modes is the electronic codebook (ECB) mode (named after conventional physical codebooks). The message is divided into blocks, and each block is encrypted separately.

• Question 163:

  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

  Correct Answer: A

  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 164:

  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

  Correct Answer: C

  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 165:

  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

  Correct Answer: C

  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 166:

  John is trying to explain the basics of cryptography to a group of young, novice, security students. Which one of the following most accurately defines encryption?

  A. Changing a message using complex mathematics

  B. Applying keys to a message to conceal it

  C. Complex mathematics to conceal a message

  D. Changing a message so it can only be easily read by the intended recipient

  Correct Answer: D

  Changing a message so it can only be easily read by the intended recipient https://en.wikipedia.org/wiki/Encryption Encryption is the process of encoding information. This process converts the original representation of the information, known as plaintext, into an alternative form known as ciphertext. Ideally, only authorized parties can decipher a ciphertext back to plaintext and access the original information. Encryption does not itself prevent interference but denies the intelligible content to a would-be interceptor.

• Question 167:

  Which of the following is a cryptographic protocol that allows two parties to establish a shared key over an insecure channel?

  A. Elliptic Curve

  B. NMD5

  C. RSA

  D. Diffie-Hellman

  Correct Answer: D

  Diffie-Hellman https://en.wikipedia.org/wiki/Diffie%E2%80%93Hellman_key_exchange Diffie-Hellman key exchange is a method of securely exchanging cryptographic keys over a public channel and was one of the first public-key protocols as originally conceptualized by Ralph Merkle and named after Whitfield Diffie and Martin Hellman. DH is one of the earliest practical examples of public key exchange implemented within the field of cryptography.

• Question 168:

  A symmetric block cipher designed in 1993 by Bruce Schneier. Was intended as a replacement for DES. Like DES it is a 16 round Feistel working on 64bit blocks. Can have bit sizes 32bits to 448bits.

  A. Skipjack

  B. Blowfish

  C. MD5

  D. Serpent

  Correct Answer: B

  Blowfish https://en.wikipedia.org/wiki/Blowfish_(cipher) Blowfish is a symmetric-key block cipher, designed in 1993 by Bruce Schneier and included in many cipher suites and encryption products. Blowfish provides a good encryption rate in software and no effective cryptanalysis of it has been found to date. However, the Advanced Encryption Standard (AES) now receives more attention, and Schneier recommends Twofish for modern applications. Blowfish has a 64-bit block size and a variable key length from 32 bits up to 448 bits. It is a 16-round Feistel cipher and uses large key-dependent S-boxes.

• Question 169:

  Modern symmetric ciphers all make use of one or more s-boxes. Both Feistel and non- Feistel ciphers use these s-boxes. What is an s-box?

  A. A substitution box where input bits are replaced

  B. A black box for the algorithm implementation

  C. A shifting box where input bits are shifted

  D. Another name for the round function

  Correct Answer: A

  Substitution box where input bits are replaced https://en.wikipedia.org/wiki/S-box In cryptography, an S-box (substitution-box) is a basic component of symmetric key algorithms which performs substitution. In block ciphers, they are typically used to obscure the relationship between the key and the ciphertext -- Shannon's property of confusion.

• Question 170:

  What size block does Skipjack use?

  A. 64

  B. 512

  C. 128

  D. 256

  Correct Answer: A

  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.