Curiously, Suetonius also writes about the nephew of Julius Caesar, Augustus Caesar also using a shift cipher. These are called shift ciphers or sometimes Caesar ciphers. While the historical reference involves shifting the alphabet by three places, we could easily perform similar ciphers with a shift of any amount between 1 and 25. Note that at the end of the alphabet we need to wrap around to the beginning of the alphabet. Decryption corresponds to the reverse process. We can think of the encryption process for this cipher for every letter of the alphabet in Table 2.1.3 where each plaintext letter (PT) will be encrypted by the letter below it in the table. Thus, our cipher text is EHZDUH WKH LGHV RI PDUFK. To encrypt the plaintext “Beware the ides of March” we shift each letter down three letters in the alphabet. Each letter of the plaintext is shifted down by three letters in the alphabet.Īs an example of how to encrypt or decrypt with this cipher, we encrypt the following famous quotation from Shakespeare's Julius Caesar. While Suetonius describes the decryption process, encryption is the reverse. In honor of Julius Caesar, this cipher is often called the Caesar cipher. If anyone wishes to 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. There are also letters of his to Cicero, as well as to his intimates on private affairs, and in the latter, 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. In The Life of Julius Caesar he writes about one of the techniques Julius Caesar used for encrypting messages in approximately 50 B.C. Suetonius, a Roman historian in the first century, wrote The Lives of the Twelve Caesars in the first century. To begin our historical journey we examine one of the oldest written references about ciphers. Probability, Permutations and Combinations.
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