ECCouncil 212-81 Practice Test - Questions Answers, Page 8

The algorithm(s) needed to encrypt and decrypt a message

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

In cryptography, a cipher (or cypher) is an algorithm for performing encryption or decryption---a series of well-defined steps that can be followed as a procedure. An alternative, less common term is encipherment. To encipher or encode is to convert information into cipher or code. In common parlance, 'cipher' is synonymous with 'code', as they are both a set of steps that encrypt a message; however, the concepts are distinct in cryptography, especially classical cryptography.

Entropy

https://en.wikipedia.org/wiki/Entropy_(information_theory)

In information theory, the entropy of a random variable is the average level of 'information', 'surprise', or 'uncertainty' inherent in the variable's possible outcomes. The concept of information entropy was introduced by Claude Shannon in his 1948 paper 'A Mathematical Theory of Communication'.

Incorrect answers:

Diffusion - transposition processes used in encryption functions to increase randomness.

Whitening - technique intended to increase the security of an iterated block cipher. It consists of steps that combine the data with portions of the key.

Collision - situation where two different inputs yield the same output.

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.

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.

Vigenre - 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.

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.

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.

Vigenre - 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.

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

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.

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.