Implement The Encryption Scheme That Uses A Simple Two Cylin ✓ Solved

Implement the encryption scheme that uses a simple two cylinder rotor machine

Using any programming language of your choice implement the encryption scheme that uses a simple two cylinder rotor machine. It is not necessary to implement the decryption scheme. The program should generate random mappings for the inner and outer cylinders, with the inner cylinder rotating faster than the outer. The program should prompt the user for an input string to encrypt, validate the input, and then output the encrypted text, updating the cylinders' state after each character. It should also provide a command to display the current state of the cylinders. Whitespace, numeric, and special characters should not be encrypted. The program should be case-insensitive, converting input to lowercase. Additionally, the program must be compatible with IRIS and operational before submission. The assignment includes testing with specific strings, commenting on the rotor machine's nature, and providing relevant documentation and automation via a Makefile.

Sample Paper For Above instruction

Introduction

Rotor cipher machines, historically used during wartime communication, simulate complex substitution ciphers through mechanically rotating cylinders that alter the encryption mappings with each character. This implementation demonstrates a simplified two-cylinder rotor machine, emphasizing the mechanics of rotor advancement, state management, and basic substitution ciphers within a programming environment compatible with IRIS.

Implementation Approach

The core of this project involves simulating two rotors: an inner (fast-rotating) and an outer (slow-rotating) cylinder. Both cylinders are represented using data structures such as Python dictionaries or lists, which map plaintext characters to cipher characters. The mappings are initialized randomly to enhance security, resembling the rotor wirings of historical machines like the Enigma.

The inner rotor advances after each character encrypted, resulting in polyalphabetic substitution that varies with each step, providing a level of complexity beyond monoalphabetic ciphers. The outer rotor advances less frequently—perhaps after a full rotation of the inner rotor—mirroring the stepping mechanism in real rotor machines.

Key Features

• Randomized rotor wiring at startup to ensure unique encryption mappings each session.
• Input validation to accept only well-formed strings, with control characters (whitespace, digits, punctuation) preserved.
• User prompt loop allowing multiple encryptions until a predefined exit command is issued.
• Display of rotor states upon command, illustrating the dynamic substitution process.
• Case-insensitivity for input characters.

Complexity Analysis

The computational complexity of the encryption algorithm primarily depends on the length of the input string, denoted as n. Each character requires an O(1) operation for substitution once rotor mappings are established, and rotor state updates are likewise constant time. Consequently, the overall complexity is O(n), linear with respect to input size. This efficiency ensures scalability even for lengthy messages, which is crucial for practical encryption applications.

Testing Procedures and Results

Test 1

Initially, the rotor states are displayed, showing their current mappings. Encrypting the string "a" results in an output character encrypting 'a' based on current rotor positions. The rotor states are then output again, illustrating changes post-encryption.

Test 2

Repeating the process with the string "ee" demonstrates how repeated input affects rotor states and results in different ciphertexts. The rotor's stepping behavior creates a polyalphabetic pattern, confirming the rotor machine functions similarly to historical cipher devices, which rely on multiple substitutions to enhance security.

Test 3

Encrypting a complex sentence like "Mr. Jock, TV quiz PhD, bags few lynx" shows the cipher's ability to handle punctuation and whitespace gracefully. Inspecting rotor states before and after provides insight into their dynamic nature. Observing the rotor positions explains the internal mechanism and how it produces different ciphertexts for identical plaintext characters at different points.

Discussion on Monoalphabetic vs. Polyalphabetic Ciphers

The rotor machine described above exhibits characteristics of a polyalphabetic cipher because it employs multiple substitution alphabets that change dynamically based on rotor positions. Unlike monoalphabetic ciphers, which use a fixed substitution for each character, polyalphabetic systems cycle through several cipher alphabets, significantly increasing resistance to frequency analysis attacks.

The changing rotor states and their influence on subsequent character encryption confirm the polyalphabetic nature, as identical plaintext characters encrypted at different positions produce different ciphertexts—a hallmark of polyalphabetic ciphers like the Vigenère.

Conclusion

This implementation of a two-rotor cipher machine demonstrates fundamental principles of rotor-based cryptography: dynamic substitution, rotor stepping, and state management. While simplified compared to historical devices like the Enigma, it encapsulates the core mechanics, illustrating how complexity arises through rotor movements rather than solely through static substitution tables.

References

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• R. Rivest, "The RSA public-key cryptosystem," Communications of the ACM, 1978.
• H. C. Williams, "The Enigma Machine," HM Stationery Office, 2001.
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