QUESTION: 37

Which of the following is a type of encryption that has two different keys. One key can encrypt the message and the other key can only decrypt it?

Block cipher
Asymmetric
Symmetric
Stream cipher

Answer(s): B

Explanation:

Asymmetric
Public-key cryptography, or asymmetric cryptography, is a cryptographic system that uses pairs of keys: public keys, which may be disseminated widely, and private keys, which are known only to the owner. The generation of such keys depends on cryptographic algorithms based on mathematical problems to produce one-way functions. Effective security only requires keeping the private key private; the public key can be openly distributed without compromising security.

Incorrect answers:
Symmetric - Symmetric-key algorithms are algorithms for cryptography that use the same cryptographic keys for both encryption of plaintext and decryption of ciphertext.
Block cipher - A block cipher is a deterministic algorithm operating on fixed-length groups of bits, called blocks. It uses an unvarying transformation, that is, it uses a symmetric key.
Stream cipher - A stream cipher is a symmetric key cipher where plaintext digits are combined with a pseudorandom cipher digit stream (keystream). In a stream cipher, each plaintext digit is encrypted one at a time with the corresponding digit of the keystream, to give a digit of the ciphertext stream.

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QUESTION: 38

Which of the following is a substitution cipher used by ancient Hebrew scholars?

Atbash
Vigenere
Caesar
Scytale

Answer(s): A

Explanation:

Atbash https://en.wikipedia.org/wiki/Atbash
Atbash is a monoalphabetic substitution cipher originally used to encrypt the Hebrew alphabet. It can be modified for use with any known writing system with a standard collating order.

Incorrect answers:
Scytale - Transposition cipher. A staff with papyrus or letter wrapped around it so edges would line up. There would be a stream of characters which would show you your message. When unwound it would be a random string of characters. Would need an identical size staff on other end for other individuals to decode message.
Vigenère - method of encrypting alphabetic text by using a series of interwoven Caesar ciphers, based on the letters of a keyword. It employs a form of polyalphabetic substitution.
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.

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QUESTION: 39

A transposition cipher invented 1918 by Fritz Nebel, used a 36 letter alphabet and a modified Polybius square with a single columnar transposition.

ADFVGX Cipher
ROT13 Cipher
Book Ciphers
Cipher Disk

Answer(s): A

Explanation:

ADFVGX Cipher https://en.wikipedia.org/wiki/ADFGVX_cipher
ADFGVX cipher was a field cipher used by the German Army on the Western Front during World War
I. ADFGVX was in fact an extension of an earlier cipher called ADFGX.
Invented by Lieutenant Fritz Nebel (1891–1977) and introduced in March 1918, the cipher was a fractionating transposition cipher which combined a modified Polybius square with a single columnar transposition.

Incorrect answers:
Book Ciphers - or Ottendorf cipher, is a cipher in which the key is some aspect of a book or other piece of text. Books, being common and widely available in modern times, are more convenient for this use than objects made specifically for cryptographic purposes. It is typically essential that both correspondents not only have the same book, but the same edition.
Cipher Disk - enciphering and deciphering tool developed in 1470 by the Italian architect and author Leon Battista Alberti. He constructed a device, (eponymously called the Alberti cipher disk) consisting of two concentric circular plates mounted one on top of the other. The larger plate is called the "stationary" and the smaller one the "moveable" since the smaller one could move on top of the "stationary"
ROT13 Cipher - simple letter substitution cipher that replaces a letter with the 13th letter after it, in the alphabet. ROT13 is a special case of the Caesar cipher which was developed in ancient Rome.

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QUESTION: 40

Message hidden in unrelated text. Sender and receiver have pre-arranged to use a pattern to remove certain letters from the message which leaves only the true message behind.

Caesar Cipher
Null Ciphers
Vigenere Cipher
Playfair Cipher

Answer(s): B

Explanation:

Null Ciphers
https://en.wikipedia.org/wiki/Null_cipher
A null cipher, also known as concealment cipher, is an ancient form of encryption where the plaintext is mixed with a large amount of non-cipher material. Today it is regarded as a simple form of steganography, which can be used to hide ciphertext.

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.
Vigenère - method of encrypting alphabetic text by using a series of interwoven Caesar ciphers, based on the letters of a keyword. It employs a form of polyalphabetic substitution.
Playfair Cipher - manual symmetric encryption technique and was the first literal digram substitution cipher. The scheme was invented in 1854 by Charles Wheatstone, but bears the name of Lord Playfair for promoting its use.

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