CryptoWorkbench/Vigenere.csharp

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

namespace AniNIX.Crypto {
    public class Vigenere : Cipher {

        public override String Description() { return "The basic Vigenere cipher\nKey format is any word to use for the passphrase"; }
        public override String Command() { return "vig"; }

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

        /// <summary>
        /// Encrypt a string with the cipher. Encryption and decryption work like a substitution but is rotated with a key.
        /// </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 inputText,String[] line) {
            if (line == null || line.Length != 3) { 
                Console.Error.WriteLine("Malformed!");
                return workSpace;
            }
            char[] changed = workSpace.ToCharArray();
            try { 
                // line[2] is the key
                int index = 0;
                for (int i =0; i < line[2].Length; i++) {
                    if (!Char.IsLetter(line[2][i])) {
                        Console.Error.WriteLine("Keys must be only letters.");
                        return workSpace;
                    }
                }
                // For each letter in the workspace, substitute with an offset given by the key. Rotate which letter in the key is used.
                for (int i = 0; i <  changed.Length; i++) {
                    if (Char.IsLetter(changed[i])) {
                        int baseC = (Char.IsUpper(changed[i])) ? (int)'A' : (int)'a';
                        int modC = (int)changed[i] - baseC;
                        int baseK = (Char.IsUpper(line[2][index])) ? (int)'A' : (int)'a';
                        int modK = (int)line[2][index] - baseK;
                        changed[i] = (char)(((modC+modK)%26)+baseC);
                        index = (index+1)%(line[2].Length);
                    }
                }
            } catch (Exception e) {
                Console.Error.WriteLine(String.Format("Failed!\n{0}",e.Message));
                return workSpace;
            }
            return new String(changed);
        }

        /// <summary>
        /// Decrypt a string with the cipher. Like the encryption method, we decrypt by removing the offset as given by the key.
        /// </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 decrypted string</returns>
        public override String Decrypt(String workSpace,String inputText,String[] line) {
            if (line == null || line.Length != 3) { 
                Console.Error.WriteLine("Malformed!");
                return workSpace;
            }
            char[] changed = workSpace.ToCharArray();
            try { 
                // line[2] is the key
                int index=0;
                for (int i = 0; i <  changed.Length; i++) {
                    if (Char.IsLetter(changed[i])) {
                        int baseC = (Char.IsUpper(changed[i])) ? (int)'A' : (int)'a';
                        int modC = (int)changed[i] - baseC;
                        int baseK = (Char.IsUpper(line[2][index])) ? (int)'A' : (int)'a';
                        int modK = (int)line[2][index] - baseK;
                        int modResult = (modC - modK)%26;
                        modResult = (modResult < 0) ? modResult+26 : modResult; // In case modResult is negative, add 26 back
                        changed[i] = (char)(modResult+baseC);
                        index = (index+1)%(line[2].Length);
                    }
                }
            } catch (Exception e) {
                Console.Error.WriteLine(String.Format("Failed!\n{0}",e.Message));
                return workSpace;
            }
            return new String(changed);

        }

    }
}