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

• Question 41:

  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

  Correct Answer: C

  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 42:

  What best describes the shifting of each letter a fixed number of spaces to the left or right?

  A. Single substitution

  B. Multi substitution

  C. XOR

  D. Bit shifting

  Correct Answer: A

  Single substitution https://en.wikipedia.org/wiki/Substitution_cipher#Simple_substitution Substitution of single letters separately--simple substitution--can be demonstrated by writing out the alphabet in some order to represent the substitution. This is termed a substitution alphabet. The cipher alphabet may be shifted or reversed (creating the Caesar and Atbash ciphers, respectively) or scrambled in a more complex fashion, in which case it is called a mixed alphabet or deranged alphabet.

• Question 43:

  DES has a key space of what?

  A. 2^128

  B. 2^192

  C. 2^64

  D. 2^56

  Correct Answer: D

  2^56 https://en.wikipedia.org/wiki/Data_Encryption_Standard The Data Encryption Standard (DES) 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 44:

  Which of the following is generally true about key sizes?

  A. Larger key sizes increase security

  B. Key size is irrelevant to security

  C. Key sizes must be more than 256 bits to be secure

  D. Smaller key sizes increase security

  Correct Answer: A

  Larger key sizes increase security https://en.wikipedia.org/wiki/Key_size Key length defines the upper-bound on an algorithm's security (i.e. a logarithmic measure of the fastest known attack against an algorithm), since the security of all algorithms can be violated by brute-force attacks. Ideally, the lower-bound on an algorithm's security is by design equal to the key length (that is, the security is determined entirely by the keylength, or in other words, the algorithm's design doesn't detract from the degree of security inherent in the key length). Indeed, most symmetric-key algorithms are designed to have security equal to their key length. However, after design, a new attack might be discovered. For instance, Triple DES was designed to have a 168 bit key, but an attack of complexity 2112 is now known (i.e. Triple DES now only has 112 bits of security, and of the 168 bits in the key the attack has rendered 56 'ineffective' towards security). Nevertheless, as long as the security (understood as 'the amount of effort it would take to gain access') is sufficient for a particular application, then it doesn't matter if key length and security coincide. This is important for asymmetric-key algorithms, because no such algorithm is known to satisfy this property; elliptic curve cryptography comes the closest with an effective security of roughly half its key length.

• Question 45:

  A _____ is a function that takes a variable-size input m and returns a fixed-size string.

  A. Feistel

  B. Asymmetric cipher

  C. Symmetric cipher

  D. Hash

  Correct Answer: D

  Hash https://en.wikipedia.org/wiki/Hash_function A hash function is any function that can be used to map data of arbitrary size to fixed-size values.

• Question 46:

  Basic information theory is the basis for modern symmetric ciphers. Understanding the terminology of information theory is, therefore, important. If a single change of a single bit in the plaintext causes changes in all the bits of the resulting ciphertext, what is this called?

  A. Complete diffusion

  B. Complete scrambling

  C. Complete confusion

  D. Complete avalanche

  Correct Answer: D

• Question 47:

  Which of the following would be the fastest.

  A. EC

  B. DH

  C. RSA

  D. AES

  Correct Answer: D

  AES https://en.wikipedia.org/wiki/Symmetric-key_algorithm AES - symmetric cipher. Symmetric keys use the same key for both encryption and decryption. Both the sender and receiver of the data must know and share the secret key. For standard encrypt/decrypt functions, symmetric algorithms generally perform much faster than their asymmetrical counterparts. This is due to the fact that asymmetric cryptography is massively inefficient. Symmetric cryptography is designed precisely for the efficient processing of large volumes of data. In other words, symmetric encryption is generally used for speed and performance, e.g. when there's a large amount of data that needs to be encrypted/protected.

• Question 48:

  Frank is trying to break into an encrypted file... He is attempting all the possible keys that could be used for this algorithm. Attempting to crack encryption by simply trying as many randomly generated keys as possible is referred to as what?

  A. Rainbow table

  B. Frequency analysis

  C. Brute force

  D. Kasiski

  Correct Answer: C

  Brute force

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

  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.

• Question 49:

  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

  Correct Answer: C

• Question 50:

  The art and science of writing hidden messages so that no one suspects the existence of the message, a type of security through obscurity. Message can be hidden in picture or audio file for example. Uses least significant bits in a file to store data.

  A. Steganography

  B. Cryptosystem

  C. Avalanche effect

  D. Key Schedule

  Correct Answer: A

  Steganography

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

  Steganography is the practice of concealing a file, message, image, or video within another file, message, image, or video.

  The first recorded use of the term was in 1499 by Johannes Trithemius in his Steganographia, a treatise on cryptography and steganography, disguised as a book on magic. Generally, the hidden messages appear to be (or to be part of)

  something else:

  images, articles, shopping lists, or some other cover text. For example, the hidden message may be in invisible ink between the visible lines of a private letter. Some implementations of steganography that lack a shared secret are forms of

  security through obscurity, and key-dependent steganographic schemes adhere to Kerckhoffs's principle.