Introduction to Cryptography - C839 Unit 1: Introduction to Cryptography. Questions and answers. Rated A+

Introduction to Cryptography - C839 Unit 1: Introduction to Cryptography. Questions and answers. Rated A+ Cryptography - -derived form the word kryptos which means "hidden," and the verb grafo, which means "Write", is the study of message secrecy Mono-Alphabet Substitution Algorithms - -These types of algorithms simply substitute one character of cipher text for each character of plain text. Examples of Mon-Alphabet Substitution Ciphers - -○ Caesar Cipher ○ Atbash Cipher ○ Affine Cipher ○ Rot13 Cipher How the Caesar Cipher works - -Every letter is shifted a fixed number of spaces to the left or right in the alphabet. Reason the Caesar Cipher is easy to crack. - -Any language has a certain letter and word frequency, meaning that some letters are used more frequently than others § In English the most common single letter word is A § The most common 3 letter word is The § The two most common two letter combinations are EE and OO. key - -the term used to describe the number that is used by the algorithm to encrypt or decrypt a message. Ciphertext - -the resultant text that is created when encryption is applied to plaintext. Atbash Cipher - -A hebrew code which substitutes the first letter of the alphabet for the last and the second letter for the second to last, etc. - simply reverses the alphabet - A becomes Z, B Becomes y, and so on. What is the basic concept of cryptography? - -To perform some permutation on plain text to render it difficult to read by those who don't have the key to decipher the cipher text Affine Cipher - -any single-substitution alphabet cipher (also called mono-alphabet substitution) in which each letter in the alphabet is mapped to some numeric value, permuted with some relatively simple mathematical function, and then converted back to a letter. What is the basic formula for an affine cipher? - -§ ax + b (mod M) □ M is the size of the alphabet; in English that equals 26 □ The x represents the plain text letter's numeric equivalent, and the b is the shift. □ The a is some multiple; in the case of the Caesar cipher, that is 1 □ So the Caesar cipher, is used by Julius Caesar, would be 1x + 3 (mod 26)