Ciphers that write message letters out diagonally over a number of rows then read off cipher row by row. Also called zig-zag cipher.
Correct Answer: A
Rail Fence Cipher https://en.wikipedia.org/wiki/Rail_fence_cipher The rail fence cipher (also called a zigzag cipher) is a form of transposition cipher. It derives its name from the way in which it is encoded. Incorrect answers: 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. Vigenere cipher - is a 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. ROT13 - ("rotate by 13 places", sometimes hyphenated ROT-13) is a 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.
Question 52
In relationship to hashing, the term _____refers to random bits that are used as one of the inputs to the hash. Essentially the ______ is intermixed with the message that is to be hashed
Correct Answer: B
Salt https://en.wikipedia.org/wiki/Salt_(cryptography) A salt is random data that is used as an additional input to a one-way function that hashes data, a password or passphrase. Salts are used to safeguard passwords in storage. Historically a password was stored in plaintext on a system, but over time additional safeguards were developed to protect a user's password against being read from the system. A salt is one of those methods. Incorrect answers: Vector - Wrong! IV - an initialization vector or starting variable (SV) is a fixed-size input to a cryptographic primitive that is typically required to be random or pseudorandom. Randomization is crucial for encryption schemes to achieve semantic security, a property whereby repeated usage of the scheme under the same key does not allow an attacker to infer relationships between segments of the encrypted message. For block ciphers, the use of an IV is described by the modes of operation. Randomization is also required for other primitives, such as universal hash functions and message authentication codes based thereon. Stream - 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. Since encryption of each digit is dependent on the current state of the cipher, it is also known as state cipher. In practice, a digit is typically a bit and the combining operation is an exclusive-or (XOR).
Question 53
Uses a formula, M_n = 2^n - 1 where n is a prime number, to generate primes. Works for 2, 3, 5, 7 but fails on 11 and on many other n values.
Correct Answer: D
Correct answers: Mersenne Primes https://en.wikipedia.org/wiki/Mersenne_prime Mersenne prime is a prime number that is one less than a power of two. That is, it is a prime number of the form M_n = 2^n - 1 for some integer n. They are named after Marin Mersenne, a French Minim friar, who studied them in the early 17th century. If n is a composite number then so is 2^n - 1. Therefore, an equivalent definition of the Mersenne primes is that they are the prime numbers of the form M_p = 2^p - 1 for some prime p. Incorrect answers: Even Numbers - A formal definition of an even number is that it is an integer of the form n = 2k, where k is an integer; it can then be shown that an odd number is an integer of the form n = 2k + 1 (or alternately, 2k - 1). It is important to realize that the above definition of parity applies only to integer numbers, hence it cannot be applied to numbers like 1/2 or 4.201. See the section "Higher mathematics" below for some extensions of the notion of parity to a larger class of "numbers" or in other more general settings. Fibonacci Numbers - commonly denoted F_n, form a sequence, called the Fibonacci sequence, such that each number is the sum of the two preceding ones, starting from 0 and 1. Co-prime Numbers - two integers a and b are said to be relatively prime, mutually prime, or coprime if the only positive integer (factor) that evenly divides both of them is 1. Consequently, any prime number that divides one of a or b does not divide the other. This is equivalent to their greatest common divisor (gcd) being 1.
Question 54
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.
Correct Answer: B
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. Vigenere - 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.
Question 55
What is a "Collision attack" in cryptography?
Correct Answer: D
Collision attacks try to find two inputs producing the same https://en.wikipedia.org/wiki/Collision_attack A collision attack on a cryptographic hash tries to find two inputs producing the same hash value, i.e. a hash collision. This is in contrast to a preimage attack where a specific target hash value is specified.
