CSCI 587 - Assignment 3 Text Encryption

1. Encode the following sentence using the simple polyalphabetic code of period three using ROT3, ROT13, ROT7.
   Carolina beat Vanderbilt.
2. Decode the text below which was encoded with a simple substitution, (not necessarily a rotation). Implemented by Substitution.c.

   mqphbeapkhqqpybstaeubpbuzpieugpkhopheghpwsbeiqX mekhpatobapzqltketupsqvqvxqseugpkhqpzboX mhqupwstjzaopmqpitjghkpkhqqpkhopyheazsqupktpxqX hqsq*ipbphqbakhpybstaeubpftsqlqspktpkhqqX

   Hint '*' is an apostrophe and '\n' is mapped to "X ", only lower case characters and a space.

3. Design an homophonic encryption code based on the frequencies of characters in English (from the handout for assignment 2). This code should be designed so that all output codes are roughly equally likely: The letters should "ZJQXK" have one code "33" of frequency .78% Every other character should have at least one output code and the number of codes should be such that the frequency was roughly 1.0%.
4. Finalize the computations on the number of initial states of:
   • the initial 3 rotor Enigma
   • the Enigma with the 7 pair plugboard
   • the final Enigma with 5 rotors of which any three could be used in any position and the plugboard
   
   Write the answer in terms of combinations and powers then expand using a calculator.
5. Given p = 101 and q = 113 Compute n, phi(n), choose b = 3533, show that b and phi(n) are relatively prime.
   Compute the private key.
6. Using the square and multiply algorithm to encode the plaintext 9726.
   Check your answer by using the private key to decode the message.