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ECCouncil 212-81 Practice Test - Questions Answers, Page 4

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Question 31

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Which of the following is generally true about key sizes?

Larger key sizes increase security
Larger key sizes increase security
Key size is irrelevant to security
Key size is irrelevant to security
Key sizes must be more than 256 bits to be secure
Key sizes must be more than 256 bits to be secure
Smaller key sizes increase security
Smaller key sizes increase security
Suggested answer: A
Explanation:

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.

asked 18/09/2024
Henry Pitcher
37 questions

Question 32

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The next number is derived from adding together the prior two numbers (1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89).

Odd numbers
Odd numbers
Fibonacci Sequence
Fibonacci Sequence
Fermat pseudoprime
Fermat pseudoprime
Prime numbers
Prime numbers
Suggested answer: B
Explanation:

Fibonacci Sequence

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

In mathematics, the Fibonacci numbers, commonly denoted Fn, form a sequence, called the Fibonacci sequence, such that each number is the sum of the two preceding ones, starting from 0 and 1. That is,

F0 = 0, F1=1, Fn = Fn-1 + Fn-2; for n > 1.

The beginning of the sequence is thus:

0,1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144...

Incorrect answers:

Prime numbers - numbers that have only 2 factors: 1 and themselves. 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47...

Fermat numbers - a positive integer of the form Fn = 2^2^n +1; where n is a non-negative integer. The first few Fermat numbers are: 3, 5, 17, 257, 65537, 4294967297, 18446744073709551617, ...

Odd numbers - any number which cannot be divided by two 1, 3, 5, 7, 9, 11, 13, 15 ...

asked 18/09/2024
Patrick Neason
44 questions

Question 33

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In a Feistel cipher, the two halves of the block are swapped in each round. What does this provide?

Diffusion
Diffusion
Confusion
Confusion
Avalanche
Avalanche
Substitution
Substitution
Suggested answer: C
Explanation:

Confusion

https://en.wikipedia.org/wiki/Confusion_and_diffusion#Definition

Confusion means that each binary digit (bit) of the ciphertext should depend on several parts of the key, obscuring the connections between the two.

The property of confusion hides the relationship between the ciphertext and the key.

This property makes it difficult to find the key from the ciphertext and if a single bit in a key is changed, the calculation of the values of most or all of the bits in the ciphertext will be affected.

Confusion increases the ambiguity of ciphertext and it is used by both block and stream ciphers.

Incorrect answer:

Avalanche - 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.

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.[2] 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.

Substitution - Substitution technique is a classical encryption technique where the characters present in the original message are replaced by the other characters or numbers or by symbols.

asked 18/09/2024
Thomas Drilling
50 questions

Question 34

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What size key does Skipjack use?

128 bit
128 bit
56 bit
56 bit
80 bit
80 bit
256 bit
256 bit
Suggested answer: C
asked 18/09/2024
Maria Telan
36 questions

Question 35

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A _____ is a function is not reversible.

Stream cipher
Stream cipher
Asymmetric cipher
Asymmetric cipher
Hash
Hash
Block Cipher
Block Cipher
Suggested answer: C
Explanation:

Hash

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

Hash functions are irreversible. This is actually required for them to fulfill their function of determining whether someone possesses an uncorrupted copy of the hashed data. This brings susceptibility to brute force attacks, which are quite powerful these days, particularly against MD5.

asked 18/09/2024
Antonio Carlos Figueiredo Junior
55 questions

Question 36

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A cryptanalysis success where the attacker discovers additional plain texts (or cipher texts) not previously known.

Total Break
Total Break
Distinguishing Algorithm
Distinguishing Algorithm
Instance Deduction
Instance Deduction
Information Deduction
Information Deduction
Suggested answer: C
Explanation:

Instance Deduction

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.

asked 18/09/2024
Taheireem Shaikh
33 questions

Question 37

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What size block does AES work on?

64
64
128
128
192
192
256
256
Suggested answer: B
Explanation:

128

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.

asked 18/09/2024
Shirish Astagikar
47 questions

Question 38

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What is Kerchoff's principle?

A minimum of 15 rounds is needed for a Feistel cipher to be secure
A minimum of 15 rounds is needed for a Feistel cipher to be secure
Only the key needs to be secret, not the actual algorithm
Only the key needs to be secret, not the actual algorithm
Both algorithm and key should be kept secret
Both algorithm and key should be kept secret
A minimum key size of 256 bits is necessary for security
A minimum key size of 256 bits is necessary for security
Suggested answer: B
Explanation:

Only the key needs to be secret, not the actual algorithm

https://en.wikipedia.org/wiki/Kerckhoffs%27s_principle

Kerckhoffs's principle of cryptography was stated by Netherlands born cryptographer Auguste Kerckhoffs in the 19th century: A cryptosystem should be secure even if everything about the system, except the key, is public knowledge.

asked 18/09/2024
Mark David
49 questions

Question 39

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When learning algorithms, such as RSA, it is important to understand the mathematics being used. In RSA, the number of positive integers less than or equal to some number is critical in key generation. The number of positive integers less than or equal to n that are coprime to n is called ______.

Mersenne's number
Mersenne's number
Fermat's number
Fermat's number
Euler's totient
Euler's totient
Fermat's prime
Fermat's prime
Suggested answer: C
Explanation:

Euler's totient

https://en.wikipedia.org/wiki/Euler%27s_totient_function

In number theory, Euler's totient function counts the positive integers up to a given integer n that are relatively prime to n.

Incorrect answers:

Fibonacci number - commonly denoted Fn, form a sequence, called the Fibonacci sequence, such that each number is the sum of the two preceding ones, starting from 0 and 1.

Fermat's number - named after Pierre de Fermat, who first studied them, is a positive integer of the form Fn = 2^2^n+1 where n is a non-negative integer. The first few Fermat numbers are:

3, 5, 17, 257, 65537, 4294967297, 18446744073709551617, ...

Mersenne prime -- prime number that is one less than a power of two. That is, it is a prime number of the form Mn = 2^n 1 for some integer n. They are named after Marin Mersenne, a French Minim friar, who studied them in the early 17th century.

asked 18/09/2024
Jonathan Dowds
45 questions

Question 40

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The Clipper chip is notable in the history of cryptography for many reasons. First, it was designed for civilian used secure phones. Secondly, it was designed to use a very specific symmetric cipher. Which one of the following was originally designed to provide built-in cryptography for the Clipper chip?

Blowfish
Blowfish
Twofish
Twofish
Skipjack
Skipjack
Serpent
Serpent
Suggested answer: C
Explanation:

Skipjack

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

The Clipper chip was a chipset that was developed and promoted by the United States National Security Agency (NSA) as an encryption device that secured ''voice and data messages' with a built-in backdoor that was intended to ''allow Federal, State, and local law enforcement officials the ability to decode intercepted voice and data transmissions.'. It was intended to be adopted by telecommunications companies for voice transmission. Introduced in 1993, it was entirely defunct by 1996.

he Clipper chip used a data encryption algorithm called Skipjack to transmit information and the Diffie--Hellman key exchange-algorithm to distribute the cryptokeys between the peers. Skipjack was invented by the National Security Agency of the U.S. Government; this algorithm was initially classified SECRET, which prevented it from being subjected to peer review from the encryption research community. The government did state that it used an 80-bit key, that the algorithm was symmetric, and that it was similar to the DES algorithm. The Skipjack algorithm was declassified and published by the NSA on June 24, 1998. The initial cost of the chips was said to be $16 (unprogrammed) or $26 (programmed), with its logic designed by Mykotronx, and fabricated by VLSI Technology, Inc (see the VLSI logo on the image on this page).

asked 18/09/2024
STEVE MESSANGA
32 questions
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