Code Making/Breaking

What methods have you seen for encoding secret messages?

Morse code Letter Jumble Decoder rings Binary code Video Game Cheat Codes Bar Codes

Codes vs. Ciphers Codes – symbols or groups of letters to represent words or phrases Ciphers – where one letter is replaced with another by a either simple or a complex scheme. –PLLX XLP= Good Dog (if L=O,P=G,X=D)

Morse Code

Binary Code

Translate this code:

Hint A = 1, B = 2, C = 3,..., Z = 26

What about this? TFNRIUJ UZV DREP KZDVJ SVWFIV KYVZI UVRKYJ; KYV MRCZREK EVMVI KRJKV FW UVRKY SLK FETV. Comes from William Shakespeare’s play Julius Caesar

This table shows the percent frequency of each letter in the English alphabet. LETTER FREQUENCY (%) LETTER FREQUENCY (%) A 7.3 N 7.8 B 0.9 O 7.4 C 3.0 P 2.7 D 4.4 Q 0.3 E 13.0 ***R 7.7 F 2.8 S 6.3 G 1.6 T 9.3 *** H 3.5 U 2.7 I 7.4 V 1.3 J 0.2 W 1.6 K 0.3 X 0.5 L 3.5 Y 1.9 M 2.5 Z 1.0 Use Letter Frequency Analysis

Hint The letter V occurs the most times (13) in the ciphertext. The letter K occurs the second most times (9) in the ciphertext. The letter R occurs the third most times (7) in the ciphertext. This is an example of a 17 letter shift, Caesar cipher

Solution Cowards die many times before their deaths; the valiant never taste of death but once.

Codes in History A Caesar cipher Caesar, Emperor of Rome B.C. letters are replaced by letters a certain distance ahead in the alphabet. (25 possible shifts) method to communicate with Roman army. generals knew the shift so they would be the only ones who could read the encrypted message

Make a Caesar Cipher “ROME IS THE GREATEST EMPIRE” Use letter wheels Make it a 7 letter shift Cipher

In Cipher form: YVTL PZ AOL NYLHALZA LTWPYL

Decode this Caesar 7 Cipher YVTL DHZ UVA IBPSA PU H KHF

Solution Rome was not built in a day

Codes in History World War II German Enigma Cipher: Machine used to encrypt and decrypt secret messages. electro-mechanical rotor machine Machine had changeable settings The total number of combinations of settings was of the order of 15,000,000,000,000,000,000, and then there is the ring-setting complication on top of this. The task facing anyone trying to decipher a particular message is to find which one of these 15 billion billion settings has been used. Enigma Demo

Codes in History Navajo Code-Talkers WW2: Syntax, tonal qualities, dialects make it unintelligible to anyone without extensive exposure and training. no alphabet or symbols spoken only on the Navajo lands of the American Southwest. less than 30 non-Navajos, none of them Japanese, could understand the language at the outbreak of World War II. Each “talker” had a body guard

Footnote on Code Talkers The U.S. Army used Choctaw code talkers to relay communications on the battlefields in France in World War I. So effective were these code talkers that after the war ended, Germany sent people to the United States to learn the languages of the American tribes. In particular, Adolf Hitler pursued experts in American Indian dialects in preparation for conquering Europe

Vigenere cipher Form of a shift code but harder to crack Based on code words Used by Confederates during the Civil War

Let’s code this: Let keyword be: “Math” MATH MA THM ATHMATHM ATHMAT. ROME IS THE GREATEST EMPIRE.

Vigenere cipher Continuing in this manner, the encoded message would be: DOFL US MOQ GKLMTXZF EFWURX.

Vigenere cipher Vigenere cipher difficult to decode, because the length of the keyword is unknown If a keyword had two letters, the number of possibilities a code breaker would have to try would be 26 2 = 576

Do Now Create a coded message for another group Supply them with keyword Exchange and decode.