Introduction to Cryptography - C839. Exam Questions and answers, rated A+

Introduction to Cryptography - C839. Exam Questions and answers, rated A+ Cryptography (or cryptology); derived from word kryptós which means "hidden," and the verb gráfo, which means "write." It is the study of message secrecy. The process or skill of communicating in or deciphering secret writings or ciphers Cesar Cipher (mono-Alphabet Substitution) You can choose to shift any number of letters, either left or right. If you choose to shift two to of a single alphabet substitution since all letters are shifted the same amount the right, that would be a +2; if you choose to shift four to the left, that would be a -4. If you get to the end of the alphabet, just keep going to the other end. So, if you are shifting to the right, and need to go past Z, just start over at A. Julius Caesar was reputed to have used a shift of three to the right. ATBASH cipher (mono-Alphabet Substitution) a Hebrew code which substitutes the first letter of the alphabet for the simply reverses the alphabet last, and the second letter for the second-to-the-last, etc. It simply reverses the alphabet. A becomes Z, B becomes Y, C becomes X. affine cipher (mono-Alphabet Substitution) ax + b (mod M) M is the size of the alphabet, so in English that would be 26. The x represents the plain text letters numeric equivalent and the b is the shift. The letter a is some multiple, in the case of the Caesar cipher that is 1. So, the Caesar cipher, as used by Julius Caesar would be 1x +3 (mod 26) ROT13 Cipher (mono-Alphabet Substitution) It is essentially the Caesar cipher always using a rotation or shift of 13 characters. This is very simple and not sophisticated enough for any real security. Scytale (mono-Alphabet Substitution) This was a cylinder tool used by the Greeks, and is often specifically attributed to the Spartans. It was a physical cylinder. And it was used by twisting to create different cyphertext. the other party only needed the same size cylinder. MAS (Multi-Alphabet Substitution) Cipher Disk (Multi-Alphabet Substitution) This, like Scytale, is a physical device used to encrypt. This was invented by Leon Alberti in 1466. The cipher disk was polyalphabetic; each time you turned the disk, you used a new cipher. It was literally a disk you turned to encrypt plaintext. Vigenère Cipher (Multi-Alphabet Substitution) invented in 1553 by Giovan Battista Bellaso. Using the chart in Figure 1-2, if you are encrypting the word "cat" and your keyword is "horse" then the result would be jok Playfair cipher (Multi-Alphabet Substitution) invented in 1854 by Charles Wheatstone. It was named after Lord Playfair who promoted the use of the cipher. "CheeseBurger" becomes "Ch ee se Bu rg er",and then you would be map out on the key table. If both letters are the same (or only one letter is left), add an "X" after the first letter. ADFGVX Cipher (Multi-Alphabet Substitution) This was the first cipher used by the German Army during World War I. It was invented by Colonel Fritz Nebel in 1918. This was a transposition cipher which used a modified Polybius square with a single columnar transposition used to encode a 36-letter alphabet. This was The first cipher used by the German Army during actually an extension of an earlier cipher called ADFGX. Homophonic substitution This was one of the earlier attempts to make substitution ciphers more robust by masking the letter frequencies. It does this by having plaintext letters map to more than one cipher text symbol. Usually the higher frequency plain text letters are given more cipher text equivalents. For example, A might map to either i or a t. This has the effect of disrupting frequencies making analysis more difficult. Having a single character of plain text map to more than one character of cipher text makes it more difficult to analyze these ciphers. Further complicating this by using symbols other than characters can make this even more difficult to analyze. Null ciphers (Homophonic substitution) Book ciphers (Homophonic substitution) Rail Fence cyphers (Homophonic substitution) enigma machine Claude Shannon