DESAFIO, TESTE DE CRIPTOGRAFIA!!!

TextoCripto = StrReverse(TextoCripto)
Dim I As Integer
For I = 1 To Len(TextoCripto)
TxtTexto = TxtTexto & Chr(Asc(Mid(TextoCripto, I, 1)) - 2)
Next I

  using System;
using System.Drawing;
using System.Collections;
using System.ComponentModel;
using System.Windows.Forms;
using System.Data;

namespace WindowsApplication1
{
	/// <summary>
	/// Summary description for Form1.
	/// </summary>
	public class Form1 : System.Windows.Forms.Form
	{
		private System.Windows.Forms.TextBox textBox1;
		private System.Windows.Forms.TextBox textBox2;
		private System.Windows.Forms.Button button1;
		private System.Windows.Forms.TextBox textBox3;
		private System.Windows.Forms.TextBox textBox4;
		/// <summary>
		/// Required designer variable.
		/// </summary>
		private System.ComponentModel.Container components = null;

		public Form1()
		{
			//
			// Required for Windows Form Designer support
			//
			InitializeComponent();

			//
			// TODO: Add any constructor code after InitializeComponent call
			//
		}

		/// <summary>
		/// Clean up any resources being used.
		/// </summary>
		protected override void Dispose( bool disposing )
		{
			if( disposing )
			{
				if (components != null) 
				{
					components.Dispose();
				}
			}
			base.Dispose( disposing );
		}

		#region Windows Form Designer generated code
		/// <summary>
		/// Required method for Designer support - do not modify
		/// the contents of this method with the code editor.
		/// </summary>
		private void InitializeComponent()
		{
			this.textBox1 = new System.Windows.Forms.TextBox();
			this.textBox2 = new System.Windows.Forms.TextBox();
			this.button1 = new System.Windows.Forms.Button();
			this.textBox3 = new System.Windows.Forms.TextBox();
			this.textBox4 = new System.Windows.Forms.TextBox();
			this.SuspendLayout();
			// 
			// textBox1
			// 
			this.textBox1.Location = new System.Drawing.Point(8, 16);
			this.textBox1.Name = "textBox1";
			this.textBox1.Size = new System.Drawing.Size(240, 20);
			this.textBox1.TabIndex = 0;
			this.textBox1.Text = "textBox1";
			// 
			// textBox2
			// 
			this.textBox2.Location = new System.Drawing.Point(8, 48);
			this.textBox2.Name = "textBox2";
			this.textBox2.Size = new System.Drawing.Size(112, 20);
			this.textBox2.TabIndex = 1;
			this.textBox2.Text = "textBox2";
			// 
			// button1
			// 
			this.button1.Location = new System.Drawing.Point(144, 48);
			this.button1.Name = "button1";
			this.button1.Size = new System.Drawing.Size(104, 24);
			this.button1.TabIndex = 2;
			this.button1.Text = "button1";
			this.button1.Click += new System.EventHandler(this.button1_Click);
			// 
			// textBox3
			// 
			this.textBox3.Location = new System.Drawing.Point(8, 80);
			this.textBox3.Name = "textBox3";
			this.textBox3.Size = new System.Drawing.Size(240, 20);
			this.textBox3.TabIndex = 3;
			this.textBox3.Text = "textBox3";
			// 
			// textBox4
			// 
			this.textBox4.Location = new System.Drawing.Point(8, 104);
			this.textBox4.Name = "textBox4";
			this.textBox4.Size = new System.Drawing.Size(240, 20);
			this.textBox4.TabIndex = 4;
			this.textBox4.Text = "textBox4";
			// 
			// Form1
			// 
			this.AutoScaleBaseSize = new System.Drawing.Size(5, 13);
			this.ClientSize = new System.Drawing.Size(264, 133);
			this.Controls.AddRange(new System.Windows.Forms.Control[] {
																		  this.textBox4,
																		  this.textBox3,
																		  this.button1,
																		  this.textBox2,
																		  this.textBox1});
			this.Name = "Form1";
			this.Text = "Form1";
			this.ResumeLayout(false);

		}
		#endregion

		/// <summary>
		/// The main entry point for the application.
		/// </summary>
		[STAThread]
		static void Main() 
		{
			Application.Run(new Form1());
		}

		private void button1_Click(object sender, System.EventArgs e)
		{
			string textoOriginal = textBox1.Text;
			string chave		 = textBox2.Text;
						
			textBox3.Text = Criptografar(textoOriginal, chave);

			textBox4.Text = Decodificar(textBox3.Text,chave);
		}

		private string Criptografar(string textoOriginal, string chave)
		{
			int auxiliar;
			string resultado = "";

			int j = 0;

			for (int i=0; i < textoOriginal.Length; i++)
			{
				auxiliar = Convert.ToByte(chave[j]) + Convert.ToByte(textoOriginal[i]);
				if (auxiliar > 255)
				{
					auxiliar = auxiliar - 255;
				}
				resultado += Convert.ToChar(auxiliar);
				
				j++;
				if (j >= chave.Length)
					j = 0;
			}

			return resultado;
		}

		private string Decodificar(string textoOriginal, string chave)
		{
			int auxiliar;
			string resultado = "";

			int j = 0;

			for (int i=0; i < textoOriginal.Length; i++)
			{
				auxiliar = Convert.ToByte(textoOriginal[i]) - Convert.ToByte(chave[j]);
				if (auxiliar < 0)
				{
					auxiliar = auxiliar + 255;
				}
				resultado += Convert.ToChar(auxiliar);
				
				j++;
				if (j >= chave.Length)
					j = 0;
			}

			return resultado;
		}
	}
}