111 lines
4.7 KiB
Plaintext
111 lines
4.7 KiB
Plaintext
using System;
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using System.Linq;
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using System.IO;
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using System.Text;
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using System.Collections.Generic;
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namespace AniNIX.Crypto {
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public class Affine : Cipher {
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public override String Description() { return "The Affine cipher\nKey format is two numbers, where the second number is coprime to the first.\n\nExample: affine encrypt 5 3\n\n"; }
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public override String Command() {return "affine";}
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public Affine(Workbench w) : base (w) {}
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/// <summary>
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/// Encrypt a string with the Affine cipher
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/// </summary>
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/// <param name="workspace">A parameter for X</param>
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/// <param name="inputText">A parameter for Y</param>
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/// <param name="line">The line given by the user</param>
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/// <returns>The return value</returns>
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public override String Encrypt(String workSpace,String inputText,String[] line) {
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// Affine requires two numbers
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if (line == null || line.Length != 4) {
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Console.Error.WriteLine("Malformed!");
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return workSpace;
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}
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char[] changed = workSpace.ToCharArray();
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try {
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// Convert the first number to an int
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int a = Int32.Parse(line[2]);
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// Validate the first number is coprime to 26.
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try {
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MultiplicativeInverse(a);
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} catch (Exception e) {
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Console.Error.WriteLine(String.Format("Value a <{0}> is not coprime to 26.\n{1}",a,e.Message));
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return workSpace;
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}
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// Convert the second number to an int
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int b = Int32.Parse(line[3]);
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// For each letter in the workSpace, apply the forumula e(x) = (ax + b) mod m
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for (int i = 0; i < changed.Length; i++) {
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if (Char.IsLetter(changed[i])) {
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int baseC = (Char.IsUpper(changed[i])) ? (int)'A' : (int)'a';
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int modC = (int)changed[i] - baseC;
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changed[i] = (char)(((a*modC+b)%26)+baseC);
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}
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}
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// If there's a problem solving, tell the user.
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} catch (Exception e) {
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Console.Error.WriteLine(String.Format("Failed!\n{0}",e.Message));
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return workSpace;
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}
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return new String(changed);
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}
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/// <summary>
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/// Find the multiplicative inverse of a number.
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/// </summary>
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/// <param name="a">A number</param>
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/// <returns>The inverse</returns>
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public int MultiplicativeInverse(int a) {
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for (int x=1; x < 27; x++) {
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//Try to find a number where the input times that number mod 26 is 1. If we roll through 26 numbers and don't find it, there isn't one.
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if ((a*x)%26 == 1) {
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return x;
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}
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}
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throw new Exception("A is not coprime.");
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}
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/// <summary>
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/// Decrypt a string with the cipher
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/// </summary>
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/// <param name="workSpace">A parameter for X</param>
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/// <param name="inputText">A parameter for Y</param>
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/// <param name="line">The user input</param>
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/// <returns>The decrypted string</returns>
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public override String Decrypt(String workSpace,String inputText,String[] line) {
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// Decryption requires two numbers.
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if (line == null || line.Length != 4) {
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Console.Error.WriteLine("Malformed!");
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return workSpace;
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}
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char[] changed = workSpace.ToCharArray();
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try {
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//Convert both numbers to ints
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int a = Int32.Parse(line[2]);
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int b = Int32.Parse(line[3]);
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//Find the multiplicative inverse of the first.
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int multiinv = MultiplicativeInverse(a);
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// For each character, decrypt with d(x) = a-1(x - b) mod m
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for (int i = 0; i < changed.Length; i++) {
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if (Char.IsLetter(changed[i])) {
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int baseC = (Char.IsUpper(changed[i])) ? (int)'A' : (int)'a';
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int modC = (int)changed[i] - baseC;
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int modResult = (multiinv * (modC-b))%26;
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modResult = (modResult < 0) ? modResult+26 : modResult; // In case modResult is negative, add 26 back
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changed[i] = (char)(modResult+baseC);
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}
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}
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} catch (Exception e) {
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Console.Error.WriteLine(String.Format("Failed!\n{0}",e.Message));
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return workSpace;
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}
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return new String(changed);
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}
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}
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}
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