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Codes

By Will Hiles. Codes. Why we did the codes?. We did the codes to celebrate Alan Turing’s 100 th anniversary. Alan Turing was an English mathematician who made the Turing machine which played a big role in the making of a modern day computer.

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Codes

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  1. By Will Hiles Codes

  2. Why we did the codes? • We did the codes to celebrate Alan Turing’s 100th anniversary. • Alan Turing was an English mathematician who made the Turing machine which played a big role in the making of a modern day computer. • During WWII he joined the Government Code and CypherSchool where he decoded German ciphers.

  3. Codes we have done • Atbash cipher • Caesar shift cipher • Substitution cipher • Frequency Analysis cipher • Homophonic cipher • Scytale Cipher • Vigenere cipher • Column Transposition Cipher • Playfair Cipher

  4. The Atbash Cipher • The Atbash cipher is a simple substitution cipher. • All As are replaced with Zs, all Bs are replaced with Ys, and so on. First 13 letters: A|B|C|D|E|F|G|H|I|J|K|L|M Last 13 Letters:Z|Y|X|W|V|U|T|S|R|Q|P|O|N • For example ‘This is a secret code’ changes to ‘Gsrhrh z hvxivgnvhhztv’

  5. Caesar shift cipher • The Caesar shift cipher is named after Julius Caesar who used for his private correspondence. • It works by taking the first 3 letters of the alphabet and putting them at the end of the alphabet. Plain: ABCDEFGHIJKLMNOPQRSTUVWXYZ Cipher:DEFGHIJKLMNOPQRSTUVWXYZABC For example: ‘the quick brown fox jumps over the lazy dog’ changes into ‘WKH TXLFN EURZQ IRA MXPSV RYHU WKH ODCB GRJ’

  6. Frequency Analysis cipher • A frequency analysis cipher is when you put your code into a frequency analysis machine. This will then tell you what the most common letters are. • The most common letters in the English language are E,T,A,O,I.

  7. Homophonic cipher • The Homophonic cipher is a difficult code to break and is designed to make frequency analysis impossible. • Each letter has multiple couplets of numbers to represent that letter. • For example "THE QUICK BROWN FOX JUMPS OVER THE LAZY DOG" could become 88-99-75 86-44-11-46-67 90-59-30-00-52 04-69-39 28-22-01-47-93 69-61-92-03 71-99-87 45-95-17-78 24-08-21.

  8. Scytale Cipher • The Scytale cipher is one of the oldest cipher from Ancient Greece. • To send secret messages during a battle a belt was wrapped around a spear (or Scytale) and a message written along the length of the spear, when the belt is unwrapped a scrambled version of the message is generated. • This is a transposition cipher because the same letters appear in the cipher text as in the original message, only the order has changed. The message can be deciphered by wrapping the belt around a spear of the same diameter, which will reveal the plaintext. • The Scytale Cipher is equivalent to writing a message along the rows of a grid and then sending the message which appears in columns. • For example the message "THEQUICKBROWNFOXJUMPSOVERTHELAZYDOG" would be sent as "TOSZHWOYENVDQFEOUORGIXTCJHKUEBMLRPA"

  9. Vigenere cipher • The Vigenere Cipher was first used in the 16th century and was extremely popular until the early 20th century. In 1836 the Mathematician Charles Dodgeson described the code as being impossible to break, and in France it was known as Le ChiffreUndechiffrable, or The unbreakable code. • The sender and receiver pick a code-word, for example BLACK, and they use each letter in the code word to form a Caesar shift cipher.

  10. Column Transposition Cipher • The column transportation cipher is like the scytale cipher except it’s more secure. • For example, you could write the message "GOOD LUCK IN THE COMPETITION" in a table with 10 columns • To increase the security they also scramble the order of the columns.

  11. The Playfair cipher • It was named after Lord Playfair. • The playfair cipher was used in the British military in the late nineteenth and early twentieth century. • The first step is to write the letters in the codeword (without repeats) in the first rows of a five by five grid, and the grid is then filled up using the remaining letters of the alphabet in order.

  12. Famous code breakers • Other famous code breakers are: Alan Turing Sir Harry Hinsley Arthur Scherbius

  13. Thank you for listening Are there any questions?

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