Question 1: How are a one-time pad and a stream cipher similar?

They both XOR bits for their encryption process.

This is Correct. The individual bits in the one-time pad are
used to encrypt the individual bits of the message through the XOR function, and in a stream algorithm the individual bits created by the keystream generator are used to encrypt the bits of the message through XOR also.

They are both asymmetric algorithms

This is Incorrect.

They are both vulnerable to linear frequency cryptanalysis attacks

This is Incorrect.

They are both block ciphers

This is Incorrect.

Question 2: Which of the following is a requirement for a secure Vernam cipher?

The pad must be used just one time

This is Correct. A one-time pad is a perfect encryption scheme because it is considered unbreakable if implemented properly. One of these requirements is that the pad is used only one time. It was invented by Gilbert Vernam in 1917, thus sometimes referred to as the Vernam cipher.

A symmetric key must be encrypted with an asymmetric key

This is Incorrect.

The private key must be only known to the owner

This is Incorrect.

It needs to hide the existence of a message

This is Incorrect.

Question 3: What type of cryptosystem commonly makes use of a passage from a well-known book for the encryption key?

Running key cipher

This is Correct. Running key (or “book”) ciphers often use a passage from a commonly available book as the encryption key.

Vernam cipher

This is Incorrect.

Skipjack cipher

This is Incorrect.

Twofish cipher

This is Incorrect.

Question 4: Which one of the following terms accurately describes the Caesar cipher?

Shift Cipher

This is Correct. The Caesar cipher is a shift cipher that works on a stream of text and is also a substitution cipher. It is not a block cipher or a transposition cipher. It is extremely weak as a cryptographic algorithm.

Block Cipher

This is Incorrect.

Transposition Cipher

This is Incorrect.

Strong Cipher

This is Incorrect.

Question 5: Which type of cipher is the Caesar cipher?

Mono-alphabetic substitution

This is Correct. The Caesar cipher is a mono-alphabetic substitution cipher. The Vigenere substitution is a polyalphabetic substitution.

Polyalphabetic transposition

This is Incorrect.

Polyalphabetic substitution

This is Incorrect.

Mono-alphabetic transposition

This is Incorrect.

Question 6: What type of cipher relies on changing the location of characters within a message to achieve confidentiality?

Transposition cipher

This is Correct.

Block cipher

This is Incorrect.

Substitution cipher

This is Incorrect.

Stream cipher

This is Incorrect.

Question 7: Which one of the following cipher types operates on large pieces of a message rather than individual characters or bits of a message?

Block Cipher

This is Correct. Block ciphers operate on message “chunks” rather than on individual characters or bits. The other ciphers mentioned are all types of stream ciphers that operate on individual bits or characters of a message.

Stream Cipher

This is Incorrect.

Caesar Cipher

This is Incorrect.

ROT3 cipher

This is Incorrect.

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