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

• Question 151:

  Which of the following asymmetric algorithms is described by U.S. Patent 5,231,668 and FIPS 186?

  A. AES

  B. RC4

  C. DSA

  D. RSA

  Correct Answer: C

  DSA https://ru.wikipedia.org/wiki/DSA The National Institute of Standards and Technology (NIST) proposed DSA for use in their Digital Signature Standard (DSS) in 1991, and adopted it as FIPS 186 in 1994. 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.

• Question 152:

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

  A. DES

  B. PGP

  C. DSA

  D. RSA

  Correct Answer: A

  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 153:

  Which of the following is an asymmetric algorithm that was first publically described in 1977?

  A. Elliptic Curve

  B. Twofish

  C. DESX

  D. RSA

  Correct Answer: D

  RSA

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

  RSA (Rivest-Shamir-Adleman) 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.

• Question 154:

  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

  Correct Answer: D

  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 155:

  Denis is looking at an older system that uses DES encryption. A colleague has told him that DES is insecure due to a small key size. What is the key length used for DES?

  A. 128

  B. 256

  C. 56

  D. 64

  Correct Answer: C

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

  The Data Encryption Standard is a symmetric-key algorithm for the encryption of digital data. Although its short key length of 56 bits makes it too insecure for applications, it has been highly influential in the advancement of cryptography.

• Question 156:

  Which of the following is not a key size used by AES?

  A. 128 bits

  B. 192 bits

  C. 256 bits

  D. 512 b

  Correct Answer: D

  512 bits 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. 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 157:

  Which of the following is an asymmetric cipher?

  A. RSA

  B. AES

  C. DES

  D. RC4

  Correct Answer: A

  RSA

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

  RSA (Rivest-Shamir-Adleman) 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.

  In a public-key cryptosystem, the encryption key is public and distinct from the decryption key, which is kept secret (private). An RSA user creates and publishes a public key based on two large prime numbers, along with an auxiliary value.

  The prime numbers are kept secret. Messages can be encrypted by anyone, via the public key, but can only be decoded by someone who knows the prime numbers.

• Question 158:

  A technique used to increase the security of block ciphers. It consists of steps that combine the data with portions of the key (most commonly using a simple XOR) before the first round and after the last round of encryption.

  A. Whitening

  B. Key Exchange

  C. Key Schedule

  D. Key Clustering

  Correct Answer: A

  Whitening https://en.wikipedia.org/wiki/Key_whitening In cryptography, key whitening is a technique intended to increase the security of an iterated block cipher. It consists of steps that combine the data with portions of the key. The most common form of key whitening is xor-encrypt-xor -- using a simple XOR before the first round and after the last round of encryption. The first block cipher to use a form of key whitening is DES-X, which simply uses two extra 64-bit keys for whitening, beyond the normal 56-bit key of DES. This is intended to increase the complexity of a brute force attack, increasing the effective size of the key without major changes in the algorithm. DES-X's inventor, Ron Rivest, named the technique whitening.

• Question 159:

  Which method of password cracking takes the most time and effort?

  A. Dictionary attack

  B. Shoulder surfing

  C. Brute force

  D. Rainbow tables

  Correct Answer: C

  Brute force

  https://en.wikipedia.org/wiki/Brute-force_attack

  A brute-force attack consists of an attacker submitting many passwords or passphrases with the hope of eventually guessing correctly. The attacker systematically checks all possible passwords and passphrases until the correct one is found.

  Alternatively, the attacker can attempt to guess the key which is typically created from the password using a key derivation function. This is known as an exhaustive key search. A brute-force attack is a cryptanalytic attack that can, in theory,

  be used to attempt to decrypt any encrypted data (except for data encrypted in an information-theoretically secure manner). Such an attack might be used when it is not possible to take advantage of other weaknesses in an encryption system

  (if any exist) that would make the task easier.

• Question 160:

  Which of the following is a block cipher?

  A. AES

  B. DH

  C. RC4

  D. RSA

  Correct Answer: A

  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