History of Cryptography

Question 1

Cryptography

Answer 1

Science of altering communication so that it cannot be understood without a key

Question 2

Mono-Alphabet Substitution Cipher

Answer 2

Algorithms that simply substitute one character of ciphertext for one character of plain text, these are the most primitive algorithm

Question 3

Caesar Cipher

Answer 3

Every letter is simply shifted a fixed number of places to the left or to the right

Question 4

Atbash Cipher

Answer 4

Hebrew cipher which substitutes the first letter of the alphabet for the last, and the second letter for the second-to-last, in other words, it simply reverses the alphabet.

Question 5

Affine Cipher

Answer 5

Any single substitution alphabet ciphers where 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.

The formula for any basic cipher of this type is ax+b(modM), M being the size of the alphabet, so for example Caeser cipher would be 1x+3(mod26)

Question 6

ROT13 Cipher

Answer 6

A single alphabet substitution cipher where all characters are rotated 13 characters through the alphabet.

Question 7

Scytale Cipher

Answer 7

Physical cylinder that was used to encrypt messages. Turning the cylinder produced different ciphertexts. Required a cylinder of the same diameter as the cylinder used to create the message to read the message.

Question 8

Single substitution weaknesses

Answer 8

Literacy rates have risen since ancient times, all languages have certain word and letter frequencies, underlying word and letter frequencies lead to vulnerability to cryptanalysis

Question 9

Examples of Multi-Alphabet Substitution

Answer 9

Cipher Disk, Vigenere Cipher

Question 10

Cipher Disk

Answer 10

Invented by Leon Alberti in 1466, physical device, each turn of the disk produces a new cipher

Question 11

Vigenere Cipher

Answer 11

Once considered very secure, invented by Giovan Battista Bellaso in 1553. Used until early 1900’s. Encrypts text by using a series of different Caesar cipher based on a keyword.

Question 12

Friedrich Kasiski

Answer 12

First-person to carry out a successful attack on a Vigenere cipher

Question 13

Playfair Cipher

Answer 13

Invented by Charles Wheatstone in 1854. Encrypts two letters instead of one, this makes it more complex. Uses a 5x5 table containing a keyword. No more secure than any other older ciphers.

Question 14

ADFVGX Cipher

Answer 14

A transposition cipher invented in 1918 by Fritz Nebel, used a 36 letter alphabet and a modified Polybius square with a single columnar transposition

Question 15

Homophonic Substitution

Answer 15

Early attempt to make substitution ciphers more robust, masks letter frequencies, plain text letters map to multiple ciphertext symbols

Question 16

Null Ciphers

Answer 16

Early attempt to make substitution ciphers more robust, masks letter frequencies, plain text letters map to multiple ciphertext symbols

Question 17

Null Ciphers

Answer 17

The message is hidden in the 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

Question 18

Book Ciphers

Answer 18

Sender and receiver agree on a particular book, coordinates are then used to locate words of an intended message in the book

Question 19

Rail Fence Cipher

Answer 19

The most widely known transposition cipher encrypts the message by altering each letter on a different row, message must then be written down the left to right and put into rows

Question 20

Enigma Machine

Answer 20

The electromechanical rotor-based cipher used in World War II

Question 21

CrypTool

Answer 21

A free tool that allows you to enter text and then choose a historical algorithm to encrypt the text