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

C839 Introduction to Cryptography. Exam Questions and answers, VERIFIED. Cryptography - -The science of altering communication so that it cannot be understood without having the key. cipher - -The algorithm(s) needed to encrypt and decrypt a message. Mono-alphabet substitution - -Substitute 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. Ciphertext - -The resultant text after being subjected to the algorithm and key. Atbash Cipher - -Reverses the alphabet ( A becomes Z, B becomes Y ... ) - Mono-Alphabet Substitution Cipher. Hebrew code. Affine Cipher - -single substitution cipher. Each letter is mapped to a numerical value, permuted with a math function and then converted back to a letter. Affine cipher formula - -ax + b (mod M) ROT13 - -One type of substitution cipher in which the entire alphabet is rotated 13 characters. Scytale - -Physical cylinder used to encrypt messages. Turning the cylinder produced different ciphers. Single substitution weaknesses - -Preserve the underlying letter and word frequency. A low-end PC is more than enough to brute force crack a single sub cipher. Multi-Alphabet Substitution - -Rotates through various keys. Cipher disk - -a physical device used to encrypt. Invented by Leon Alberti in 1466. The cipher disk was polyalphabetic; each time you turned the disk, you used a new cipher. Vignere cipher - -Invented in 1553 by Giovan Battista Bellaso. A method of encrypting text by applying a series of different mono-alphabet ciphers based on the letters of a keyword. Playfair Cipher - -Invented by Charles Wheatstone in mid 1800s. Lord Playfair pushed use of it. Uses a 5x5 table and a key word. Rest of the alphabet is placed on table in alphabetic order, skipping letters used in the keyword. You break