Introduction to Cryptography - C839. Exam Questions and answers. VERIFIED.

Introduction to Cryptography - C839. Exam Questions and answers. VERIFIED. - Cipher - Key - Algorithm - -- The algorithm(s) needed to encrypt and decrypt a message. - The random bits used in encrypting a message. - The mathematical process used to alter a message and read it unintelligible by any but the intended party Stream Cipher - -Uses a keystream generator and encrypts a message one bit at a time, usually implemented in hardware. Popular when data comes in long streams (such as with older wireless networks or cell phones). Attack Tree - -A branching, hierarchical data structure that represents a set of potential techniques for exploiting security vulnerabilities Defense in Depth - -A defense that uses multiple types of security devices to protect a network. Also called layered security. Threat analysis/assessment - -An evaluation of the type, scope, and nature of events or actions that can result in adverse consequences; identification of the threats that exist against enterprise assets. It usually defines the level of threat and the likelihood of it materializing. Cryptography - -The science of altering communication so that it cannot be understood without having the key - Substituting one character of cipher text for each character of plain text - Caesar Cipher: Every letter is shifted a fixed number of spaces to the left or the right in the alphabet; single alphabet substitution - Atbash Cipher: Hebrew code which reverses the alphabet - Affine Cipher: Single-substitution; converts a letter to a number, passes it through a mathematical function of ax + b (mod M), and then converts it back to a letter - Rot13 Cipher: All characters are rotated 13 spaces through the alphabet; basically the Caesar cipher using a +13 shift - -- What is mono-alphabet substitution? - What are four examples of this method? - Plaintext - Ciphertext - -- Normal text that has not been encrypted - Text which has been encrypted through an algorithm and key Scytale - -A tool used to perform a transposition cipher, consisting of a cylinder with a strip of parchment wound around it on which is written a message; from the Greeks - When you rotate through various alphabets instead of only one. For example, doing shifts of +1, -1, and +2 - Cipher Disk: invented by Leon Alberti in 1466. A physical disk where each time you turn it, you are using a new cipher - Vigenère Cipher: Invented in 1553 by Giovan Battista Bellaso; uses a series of different Caesar ciphers based on the letters of a keyword; the longer the keyword, the stronger the encryption - Enigma Machine: an electromechanical rotor based cipher system used by Germans in WWII. Last of the historical ciphers - -- What is a multi-alphabet substitution? - What are three examples? Playfair Cipher - -Cipher from the mid-1800s which encrypts two letters at a time. More complex than other alphabet ciphers but not really any more secure or difficult to crack. Complexity does not equal security.