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Caesar Cipher Script1B|08 Avril, Lorenzo, Tze HernINTRODUCTIONA very good morning to one and all, we are group 3 and our presentation for today in on a classical cipher: Caesar’s Cipher. I’m Avril, he’s Tze Hern and that’s Lorenzo. Here is an overview of what we’ll be covering today. I’ll be sharing about the history and development of the Caesar’s Cipher, while Tze Hern will describe how it is used. Lorenzo will round up our presentation with the pros and cons of this cipherand how to break it.HISTORY & DEVELOPMENTNamed after Julius Caesar. It was used during 50BC by notable Romans including Julius CaesarIn cryptography, the Caesar cipher is also known as Caesar’s shift or the ShiftcipherJulius Caesar used the Caesar cipher to communicate with his generals during military campaigns to protect/ encrypt messages important to the military and the government.It is a type of substitution cipher. Each letter in the plaintextis replaced by a letter some fixed number of positions further down the alphabet.The Caesar cipher is a “monoalphabetic substitution cipher”, meaning only one letter is assigned to the alphabet it is supposed to representAccording to Suetonius, who wrote the book Life of Julius Caesar,Julius Caesar used the substitution cipher to a shift of three. This means that he shifted each letter 3 places further through the alphabet. a(plaintext) becomes D(cipher)“If he had anything confidential to say, he wrote it in cipher, that is, by so changing the order of the letters of the alphabet, that not a word could be made out. If anyone wishesto decipher these, and get at their meaning, he must substitute the fourth letter of the alphabet, namely D, for A, and so with the others” -Suetonius,Life of Julius Caesar 56Julius Caesar’s nephew, Augustus, also used the Caesar cipher. However, he used it to the shift of one According to David Kahn’s book, The Codebreakers, lovers used the Caesar code to communicate secretly.The plaintext is usually in lower case but the cipher text is in upper case.The ROT13 is an application of the Caesar cipher. ROT13 replaces each letter by its partner 13 characters further down the alphabet. As the alphabet consist of 26 letters, the “ROT13 function is its own inverse”, meaning C becomes P and P becomes C.HOW TO USEThe Caesar Cipher replaces each letter in the plain text (the alphabet) with a letter that has a fixed number of places down the alphabet. For example, the diagram below has defined its parameters with a shift of 3 also known as the Caesar shift.As such, the letterBin the plaintext becomes Einthe ciphertext. Here is a sample of the revolvable cipherwhich makes encryption much more convenient by turning the inner and outer wheel. The outer wheel is the original alphabet or plaintext and the inner wheel is the ciphertext which can be adjusted accordingly. PROS & CONSThe good points of the Caesar cipher is that it is very simple to use. All a person has to do is to write out his message and then referring to his cipher, rewrite his message again, now encrypted. To give the recipient the key, one can just tell them for example “move back 3′′ so ‘c’ wouldbe represented by ‘z’, and ‘d’ would be represented by ‘a’.No machines or devices are needed to decode it. Apaper and pen for conveniencemay be all that you need. The bad points are that due to the nature of the cipher, an encrypted text has only 26 possibilities, 25 not including the given text. Within 5 minutes, an experienced cryptobreaker
Caesar Cipher Script1B|08 Avril, Lorenzo, Tze Herncould crack the code. Anyone else could crack the code in 10 minutes. With the revolvable cipher, anyone could crack the code in 4-5 minutes. The key could be obtained through trial and error.This is called a Brute Force Attack.To save time a series of strips could be prepared. Each with 52 letters, the letters would be in alphabetical order twice over. The strips would be aligned so that the ciphertext read in one position.They would then be scanned to reveal the plaintext.An alternative and quicker way to guessing/trial and error is through observing the frequency of the letters.Here is a diagramrepresenting the frequency of the lettersin the alphabet.For example, if a certain letter ‘z’ for example is noticed to be repeated very often in the ciphertext, you could start off by guessing that’z’ represents ein the plaintext, which is the most commonly used letter. Subsequently you can use this method to determine the rest of the letters.We have now come to the end of our presentation;here is a list of the web-based material we have referenced. Thank you and have a nice day. BIBLIOGRAPHYhttp://en.wikipedia.org/wiki/Caesar_cipherhttp://www.murky.org/blg/the-caesar-shift/Chris Savarese and Brian Hart, The Caesar Cipher, 1999F.L. Bauer, Decrypted Secrets,2nd edition, 2000, SpringerDavid Kahn, The Codebreakers —The Story of Secret Writinghttp://www.spiritus-temporis.com/caesar-cipher/history-and-usage.htmlhttp://en.wikipedia.org/wiki/ROT13http://all.net/BOOKS/IP/cHAP2-1.HTML