13. Strings and Text Processing 7. Encrypt

using System;
using System.Text;

class EncryptDecrypt
{
    static void Main()
    {
        string str = "Some text for crypting and decrypting!";
        string key = "The key";

        Console.Write("Encrypted =>    ");
        string encrypted = Encrypt(str, key);
        Console.WriteLine(encrypted);

        Console.Write("Decrypted =>   ");
        string deCrypt = DeCrypt(encrypted, key);
        Console.WriteLine(deCrypt);
    }
    static string Encrypt(string str, string key)
    {
        char[] strArr = str.ToCharArray();
        char[] keyArr = new char[strArr.Length];

        StringBuilder encrypted = new StringBuilder();

        for (int i = 0, k = 0; i < keyArr.Length; k++, i++)
        {
            if (!(k < key.Length))
            {
                k = 0;
            }
            keyArr[i] = key[k];
        }
        for (int i = 0; i < strArr.Length; i++)
        {
            encrypted.Append((char)(strArr[i] ^ keyArr[i]));
        }
        return encrypted.ToString();
    }
    static string DeCrypt(string str, string key)
    {
        return Encrypt(str, key).ToString();
    }
}