QUESTION: 29

DES has a key space of what?

2^128
2^192
2^64
2^56

Answer(s): D

Explanation:

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.

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QUESTION: 30

John works as a cryptography consultant. He finds that people often misunderstand the reality of breaking a cipher. What is the definition of breaking a cipher?

Finding any method that is more efficient than brute force
Uncovering the algorithm used
Rendering the cypher no longer useable
Decoding the key

Answer(s): A

Explanation:

Finding any method that is more efficient than brute force. https://en.wikipedia.org/wiki/Cryptanalysis
Bruce Schneier notes that even computationally impractical attacks can be considered breaks: "Breaking a cipher simply means finding a weakness in the cipher that can be exploited with a complexity less than brute force. Never mind that brute-force might require 2^128 encryptions; an attack requiring 2^110 encryptions would be considered a break...simply put, a break can just be a certificational weakness: evidence that the cipher does not perform as advertised."

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QUESTION: 31

____________ uses at least two different shifts, changing the shift with different letters in the plain text.

Caesar cipher
multi-alphabet encryption
Scytale
Atbash

Answer(s): B

Explanation:

multi-alphabet encryption https://en.wikipedia.org/wiki/Polyalphabetic_cipher Two different shifts create two different alphabets. For +1 and +2
Plaintext alphabet
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
2 ciphertext alphabets
B C D E F G H I J K L M N O P Q R S T U V W X Y Z A
C D E F G H I J K L M N O P Q R S T U V W X Y Z A B

Incorrect answers:
Scytale - transposition cipher
Caesar cipher - monoalphabetic cipher
Atbash - monoalphabetic cipher

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QUESTION: 32

Jane is looking for an algorithm to ensure message integrity. Which of following would be an acceptable choice?

RSA
AES
RC4
SHA-1

Answer(s): D

Explanation:

Integrity. In information security, data integrity means maintaining and assuring the accuracy and completeness of data over its entire lifecycle. This means that data cannot be modified in an unauthorized or undetected manner.
An important application of hashes is verification of message integrity. Comparing message digests (hash digests over the message) calculated before, and after, transmission can determine whether any changes have been made to the message or file.
SHA-1
https://en.wikipedia.org/wiki/SHA-1

SHA-1 (Secure Hash Algorithm 1) is a cryptographic hash function which takes an input and produces a 160-bit (20-byte) hash value known as a message digest – typically rendered as a hexadecimal number, 40 digits long. It was designed by the United States National Security Agency, and is a U.S. Federal Information Processing Standard.
Incorrect answers:
RSA (Rivest–Shamir–Adleman) is one of the first public-key cryptosystems and is widely used for secure data transmission.
RC4 (Rivest Cipher 4 also known as ARC4 or ARCFOUR meaning Alleged RC4, see below) is a stream cipher.
AES (Advanced Encryption Standard) is a subset of the Rijndael block cipher

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QUESTION: 31

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