CryptoWorkbench/Substitution.csharp

using System;
using System.IO;
using System.Text;
using System.Collections.Generic;

namespace AniNIX.Crypto {
    public class Substitution : Cipher {

        public char[] EngCommon = {'e','t','a','o','i','n','s','h','r','d','l','u','c','m','w','f','y','g','p','b','v','k','x','j','q','z'};

        public override String Description() { return "Substitution ciphers replace characters one-for-one.\nKey format is \"E[EEE]=d[ddd]\", where E is the character in the cipher and d is the intended character in the workspace.\n\nSubstitution can take multiple keys in a single invocation.\n\nExample usage:\nsub decrypt I=j       -- replace each I in the input with j in the workspace.\nsub decrypt IN=jq     -- replace each I in the input with j in the workspace, and each N in the input with q.\nsub decrypt IN=jq K=c -- do the above, and additionally replace each K with c.\n"; }
        public override String Command() { return "sub"; }

        public Substitution(Workbench w) : base (w) {}

        /// <summary> 
        /// We should be able to act on a workspace and command line. Most ciphers will sue the same syntax. Those that don't can override.
        /// </summary>
        /// <param name=workSpace>The current version of the text being worked on.</param>
        /// <param name=line>The command sequence.</param>
        /// <returns>The updated version of the workSpace</returns> 
        public  override String RunCommand(String workSpace,String inputText,String[] line) {
            if (workSpace == null || line == null || line.Length < 2) {
                Console.Error.WriteLine("Malformed request.");
                return workSpace;
            }
            switch (line[1]) {
                case "encrypt": 
                    return Encrypt(workSpace,inputText,line);
                case "decrypt":
                    return Decrypt(workSpace,inputText,line);
                case "try-common": 
                    return TryCommon(inputText);
                case "help": 
                case "":
                    GetHelp();
                    return workSpace;
                default:
                    Console.Error.WriteLine("Invalid command. Type help for more.");
                    return workSpace;
            }
        }

        /// <summary>
        /// Show the helptext for this cipher. By default, most ciphers will only have encrypt, decrypt, and help functions.
        /// </summary>
        /// <param name=line>This is the incoming line and we use it to get the cipher name</param>
        public  override void GetHelp() {
            Console.WriteLine(String.Format("Help for the {0} cipher suite.\n{1}\n",Command(),Description()));
            Console.WriteLine("Usage:\nsub encrypt key[s]     -- encrypt with the key[s]\nsub decrypt key[s]     -- decrypt with the key[s]\ntry-common            -- try common sub keys\nhelp                  -- show this helptext.");
        }

        /// <summary>
        /// Encrypt a string with the cipher, replacing one character with another. 
        /// </summary>
        /// <param name="workSpace">The working copy of the cipher</param>
        /// <param name="inputText">The original cipher</param>
        /// <param name="line">The user input</param>
        /// <returns>The encrypted string</returns>
        public override String Encrypt(String workSpace, String cipher, String[] line) {
            if (line.Length < 3) {
                Console.Error.WriteLine("Bad formatting.");
                return workSpace;
            }
            char[] changed = workSpace.ToCharArray();
            for (int i=2; i<line.Length;i++) {
                if (line[i].Length < 3 || line[i].Length%2 != 1 || line[i][line[i].Length/2] != '=') {
                    Console.Error.WriteLine("Bad substitution. Aborting.");
                    return workSpace;
                }
                // For each key-value pair...
                for (int k = 0; k < line[i].Length/2; k++) {
                    char oldS = line[i].Substring(k,1)[0];
                    char newS = line[i].Substring(k+line[i].Length/2+1,1)[0];
                    Console.WriteLine(String.Format("Replacing cipher {0} to be workspace {1}",oldS,newS));
                    // for each character in the workspace...
                    for (int j = 0; j < workSpace.Length; j++) {

                        // replace the old character with the requested replacement.
                        if (cipher[j] == oldS) {
                            changed[j] = newS;
                        }
                    }   
                }                
            }
            return new String(changed);
        }

        
        // This is a dummy for encrypt -- the functions are the same.
        public  override String Decrypt(String workSpace, String cipher, String[] line) {
            return Encrypt(workSpace, cipher, line);
        }

        /// <summary> 
        /// Perform a frequency analysis and see if ETAOIN substitution will solve the problem. TODO this should look at a dictionary for confirmation.
        /// </summary>
        /// <param name="workSpace"> the string to analyze and brute-force</param>
        /// <returns> an attempted solution. </returns>
        public  String TryCommon(String workSpace) {
            // Get the frequency analysis
            List<String> sortedChars = Analysis.GetMostCommonLetters(workSpace.ToLower());
            // Strip to lower for now and replace. TODO ensure all manipulation is done in lower case and restored later.
            char[] modified = workSpace.ToLower().ToCharArray();
            char replaceChar;
            // For each character in the string, replace with its frequency map equivalent.
            for (int i = 0; i < modified.Length; i++) { 
                if (!Char.IsLetter(modified[i])) { continue; }
                Console.WriteLine(String.Format("Character <{0}> occurs {1}st in frequency, corresponding with <{2}> -- replacing...",
                            modified[i],
                            sortedChars.IndexOf(modified[i].ToString()),
                            EngCommon[sortedChars.IndexOf(modified[i].ToString())]));
                replaceChar = EngCommon[sortedChars.IndexOf(modified[i].ToString())];
                replaceChar = (workSpace[i] == Char.ToLower(workSpace[i])) ? replaceChar : Char.ToUpper(replaceChar);
                modified[i] = replaceChar;
            }
            return new String(modified);
        }
    }
}