สอบถามเรื่องการเข้ารหัสและการถอดรหัส สำหรับใช้กับรหัสผ่านของระบบ Login ครับ

using System;
using System.Security.Cryptography;
using System.Text;

namespace SoftwareTest
{
	/// <summary>
	/// Summary description for Security.
	/// </summary>
	public class Security
	{
		public Security()
		{
			//
			// TODO: Add constructor logic here
			//
		}
		public static string Encrypt(string pCleanString) {
			Byte[] clearBytes = new UnicodeEncoding().GetBytes(pCleanString);
			Byte[] hashedBytes = ((HashAlgorithm) CryptoConfig.CreateFromName("MD5")).ComputeHash(clearBytes);
			
			return BitConverter.ToString(hashedBytes);
		}

		public static string base64Encode(string data)
		{
			try
			{
				byte[] encData_byte = new byte[data.Length];
				encData_byte = System.Text.Encoding.UTF8.GetBytes(data);    
				string encodedData = Convert.ToBase64String(encData_byte);
				return encodedData;
			}
			catch(Exception e)
			{
				throw new Exception("Error in base64Encode" + e.Message);
			}
		}

		public string base64Decode(string data)
		{
			try
			{
				System.Text.UTF8Encoding encoder = new System.Text.UTF8Encoding();  
				System.Text.Decoder utf8Decode = encoder.GetDecoder();
    
				byte[] todecode_byte = Convert.FromBase64String(data);
				int charCount = utf8Decode.GetCharCount(todecode_byte, 0, todecode_byte.Length);    
				char[] decoded_char = new char[charCount];
				utf8Decode.GetChars(todecode_byte, 0, todecode_byte.Length, decoded_char, 0);                   
				string result = new String(decoded_char);
				return result;
			}
			catch(Exception e)
			{
				throw new Exception("Error in base64Decode" + e.Message);
			}
		}
	}
}

		 	require_once('PHPMailer/class.phpmailer.php');
		 	$mail = new PHPMailer();
		 	$mail->IsHTML(true);
		 	$mail->IsSMTP();
		 	$mail->SMTPAuth = true; // enable SMTP authentication
		 	$mail->SMTPSecure = "ssl"; // sets the prefix to the servier
		 	$mail->Host = "smtp.gmail.com"; // sets GMAIL as the SMTP server
		 	$mail->Port = 465; // set the SMTP port for the GMAIL server
		 	$mail->Username = "อีเมล์ที่ใช้ส่ง@gmail.com"; // GMAIL username
		 	$mail->Password = "รหัสผ่าน Gmail"; // GMAIL password
		 	$mail->From = "[email protected]"; // "[email protected]";
		 	$mail->FromName = "Mr.Tester";  // set from Name
		 	$mail->Subject = "Test sending mail.";
		 	$mail->Body = "My Body & <b>My Description</b>";

		 	$mail->AddAddress("อีเมล์ผู้รับ@gmail.com", "Mr.Receive Tester"); // to Address

		 	$mail->set('X-Priority', '1'); //Priority 1 = High, 3 = Normal, 5 = low
		 	$mail->Send();