QUESTION: 41

Cryptographic hashes are often used for message integrity and password storage. It is important to understand the common properties of all cryptographic hashes. What is not true about a hash?

Few collisions
Reversible
Variable length input
Fixed length output

Answer(s): B

Explanation:

Reversible https://en.wikipedia.org/wiki/Hash_function Hash functions are not reversible.

Incorrect answers:
Fixed length output and Variable length input. Hash function receive variable length input and produce fixed length output
Few collisions. Every hash function with more inputs than outputs will necessarily have collisions

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QUESTION: 42

John is going to use RSA to encrypt a message to Joan. What key should he use?

A random key
Joan’s public key
A shared key
Joan’s private key

Answer(s): B

Explanation:

Joan’s public key
https://en.wikipedia.org/wiki/RSA_(cryptosystem)
Suppose Joahn uses Bob's public key to send him an encrypted message. In the message, she can claim to be Alice but Bob has no way of verifying that the message was actually from Alice since anyone can use Bob's public key to send him encrypted messages. In order to verify the origin of a message, RSA can also be used to sign a message. Suppose Alice wishes to send a signed message to Bob. She can use her own private key to do so. She produces a hash value of the message, raises it to the power of d (modulo n) (as she does when decrypting a message), and attaches it as a "signature" to the message. When Bob receives the signed message, he uses the same hash algorithm in conjunction with Alice's public key. He raises the signature to the power of e (modulo n) (as he does when encrypting a message), and compares the resulting hash value with the message's actual hash value. If the two agree, he knows that the author of the message was in possession of Alice's private key, and that the message has not been tampered with since.

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QUESTION: 43

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

Feistel
Asymmetric cipher
Symmetric cipher
Hash

Answer(s): D

Explanation:

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.

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QUESTION: 44

The most widely used asymmetric encryption algorithm is what?

Vigenere
Caesar Cipher
RSA
DES

Answer(s): C

Explanation:

RSA
The RSA encryption algorithm is one of the most widely used public key encryption algorithms that have ever been invented. It was created by the three scientists Ronald Rivest, Adi Shamir, and Leonard Adleman in 1977, and today it is increasingly being used in the network area.

Incorrect answers:
Caesar Cipher - Monoalphabetic cipher where letters are shifted one or more letters in either direction. The method is named after Julius Caesar, who used it in his private correspondence.
Vigenere - Multi alphabet cipher Invented by Giovan Battista Bellaso in middle 1553. Vigenere created a stronger version of the cipher. Combining/Weaving Caesar cipher. Not cracked until late 1800s. Widely used from 16th century to early 20th century. It is a cipher square with A to Z across all the columns and rows. You then use a keyword to encrypt the message
DES - The Data Encryption Standard is a symmetric-key algorithm for the encryption of digital data.

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