Midterm Project - the Trithemius Cipher Spring 2017

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Midterm Project - The Trithemius Cipher Spring 2017 This project should consist of a short written report which includes your responses for the questions and exercises below. Include a bibliography of sources you used. 1. Who was Johannes Trithemius and when did he live? Was his cipher created before or after the Alberti Cipher? Was it a monoalphabetic or polyalphabetic cipher? Why? Why is it important? 2. Describe how the Trithemius cipher was used. Compare it to the Alberti cipher. Explain what a \progressive key cipher" is. Write out a tabula recta and explain how it was used in the encoding process. How is it different from the Vigenere cipher? 3. Now encrypt the message Cryptography is fun using the Trithemius cipher where you start with the first column of the tabula recta. Do not encrypt spaces. Explain your steps. What key, if any, does the receiver need to decrypt the message? 4. Now decrypt the message JPJDRSKZBASETRAXKJ using the Trithemius cipher where it was encrypted by starting with the first column of the tabula recta. Explain your steps. 5. This cipher is not very secure. One option to improve it, would be start with a column other than the first in the tabula recta. This would be the key that the decoder needs. (a) Encrypt the message Cryptography is fun using the Trithemius cipher and a key of 20 (the starting column number). (b) Now decrypt the message SUSMB where it was encrypted by starting with a random column. Explain your reasoning to decrypt it. How does the decryption process compare with a shifted Caesar cipher? Is it more secure? Why? 6. Another approach to making this more secure is to basically have two (or more) alphabets which are indicated by the starting column; e.g., 10 and 20 or the starting letters \J' and \T". The first letter of the message (assume it is HELP) is encrypted in the usual manner using alphabet 1; for example if we start with the column where\J" is at the top we encrypt \H" as \Q". The second letter of the message is \E" and we use the second alphabet, i.e., we look at the column with \T" at the top and see that we encrypt \E" as \X". To encrypt the \L" we return to the first alphabet which started at column 10 and so now we progress to column 11 and see that it is encrypted as \V'. Lastly we encrypt \P" using the second alphabet so we use column 21 to get \J". Of course we can use more than two alphabets. (a) Encrypt the message \Cryptography is fun" using a key of columns 5 and 12. (b) Encrypt the message \Cryptography is fun" using a key word (which indicates the column numbers) \FSU". 1.

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International Journal of Integrated Engineering: Special Issue 2018: Data Information Engineering, Vol. 10 No. 6 (2018) p. 183-192. © Penerbit UTHM DOI: https://doi.org/10.30880/ijie.2018.10.06.026 Analysis of Four Historical Ciphers Against Known Plaintext Frequency Statistical Attack Chuah Chai Wen1*, Vivegan A/L Samylingam2, Irfan Darmawan3, P.Siva Shamala A/P Palaniappan4, Cik Feresa Mohd. Foozy5, Sofia Najwa Ramli6, Janaka Alawatugoda7 1,2,4,5,6Information Security Interest Group (ISIG), Faculty Computer Science and Information Technology University Tun Hussein Onn Malaysia, Batu Pahat, Johor, Malaysia E-mail: [email protected], [email protected], {shamala, feresa, sofianajwa}@uthm.edu.my 3School of Industrial Engineering, Telkom University, 40257 Bandung, West Java, Indonesia 7Department of Computer Engineering, University of Peradeniya, Sri Lanka E-mail: [email protected] Received 28 June 2018; accepted 5August 2018, available online 24 August 2018 Abstract: The need of keeping information securely began thousands of years. The practice to keep the information securely is by scrambling the message into unreadable form namely ciphertext. This process is called encryption. Decryption is the reverse process of encryption. For the past, historical ciphers are used to perform encryption and decryption process. For example, the common historical ciphers are Hill cipher, Playfair cipher, Random Substitution cipher and Vigenère cipher. This research is carried out to examine and to analyse the security level of these four historical ciphers by using known plaintext frequency statistical attack. The result had shown that Playfair cipher and Hill cipher have better security compare with Vigenère cipher and Random Substitution cipher.
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