数字签名里验证签名的函数出问题了，求帮助

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.IO;
using System.Security.Cryptography;

namespace WindowsFormsApplication1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        //生成公私密钥对，并将其保存在密钥容器中，导出公钥
        public static string GenKey_SaveInContainer(string ContainerName)
        {
            FileStream fs = new FileStream("e:\\Public_Key.txt", FileMode.Open, FileAccess.ReadWrite);
            
            CspParameters cp = new CspParameters();
            cp.KeyContainerName = ContainerName;
            cp.KeyNumber = (int)KeyNumber.Signature;                                           //"1" = Exchanger, 为交换密钥             
            cp.Flags = CspProviderFlags.UseMachineKeyStore;
            RSACryptoServiceProvider RSAalg = new RSACryptoServiceProvider(cp);
            string str_Private_Key = Convert.ToBase64String(RSAalg.ExportCspBlob(true));  //true 私钥
            string str_Public_Key = Convert.ToBase64String(RSAalg.ExportCspBlob(false));
                        
            StreamWriter sw = new StreamWriter(fs);
            fs.SetLength(0);
            sw.Write(str_Public_Key);
            sw.Close();
            fs.Close();

            return str_Private_Key;
        }
        
        //  载入待签名的文件
        private void button1_Click(object sender, EventArgs e)
        {
            OpenFileDialog file = new OpenFileDialog();
            if (file.ShowDialog() == DialogResult.OK)
            {
                textBox1.Text = file.FileName;
            }
        }

        //  载入公钥
        private void button2_Click(object sender, EventArgs e)
        {
            OpenFileDialog file = new OpenFileDialog();
            if (file.ShowDialog() == DialogResult.OK)
            {
                textBox2.Text = file.FileName;
            }
        }

        //  载入数字签名
        private void button3_Click(object sender, EventArgs e)
        {
            OpenFileDialog file = new OpenFileDialog();
            if (file.ShowDialog() == DialogResult.OK)
            {
                textBox3.Text = file.FileName;
            }
        }

        //  生成数字签名
        private void button4_Click(object sender, EventArgs e)
        {
            string ContainerName = "信安课设";
            string privatekey = GenKey_SaveInContainer(ContainerName);
            textBox4.Text = privatekey;
            richTextBox1.Text = HashAndSign(textBox1.Text, ContainerName,privatekey);
        }

        //数字签名
        private string HashAndSign(string path, string ContainerName, string privatekey)
        {
            ASCIIEncoding ByteConverter = new ASCIIEncoding();
            FileStream file = new FileStream(path, FileMode.Open, FileAccess.Read, FileShare.Read);
            MD5CryptoServiceProvider md5 = new MD5CryptoServiceProvider();

            CspParameters cp = new CspParameters();
            cp.KeyContainerName = ContainerName;
            cp.KeyNumber = (int)KeyNumber.Signature;                                           //"1" = Exchanger, 为交换密钥             
            cp.Flags = CspProviderFlags.UseMachineKeyStore;

            byte[] DataToSign = new byte[file.Length];
            file.Read(DataToSign, 0, (int)file.Length);                   //将文档流读取到Buffer中
            file.Close();
            //byte[] DataToSign = ByteConverter.GetBytes(str_DataToSign);     //字符串转字节流
            try
            {
                RSACryptoServiceProvider RSAalg = new RSACryptoServiceProvider(cp);

                RSAalg.ImportCspBlob(Convert.FromBase64String(privatekey));  //导入RSA密钥
                byte[] signedData = RSAalg.SignData(DataToSign, typeof(MD5));   //Hash 并签名
                string str_SignedData = Convert.ToBase64String(signedData);

                return str_SignedData;
            }
            catch (CryptographicException e)
            {
                Console.WriteLine(e.Message);
                return null;
            }
        }

        //  导出数字签名
        private void button5_Click(object sender, EventArgs e)
        {
            string Signed = richTextBox1.Text;
            string path = "e:\\digital signature.txt";

            FileStream fs = new FileStream(path, FileMode.Open, FileAccess.ReadWrite);
            StreamWriter sw = new StreamWriter(fs);
            fs.SetLength(0);
            sw.Write(Signed);
            sw.Close();
            fs.Close();
        }

        //  验证数字签名
        private void button6_Click(object sender, EventArgs e)
        {
            try
            {
                MD5CryptoServiceProvider md5 = new MD5CryptoServiceProvider();

                FileStream fs = new FileStream(textBox1.Text, FileMode.Open, FileAccess.Read, FileShare.Read);
                byte[] DataToVerify = new byte[fs.Length];
                fs.Read(DataToVerify, 0, (int)fs.Length);
                fs.Close();
                //string data = Encoding.ASCII.GetString(DataToVerify);
                //DataToVerify = Encoding.UTF8.GetBytes(data);

                FileStream fs1 = new FileStream(textBox3.Text, FileMode.Open, FileAccess.Read, FileShare.Read);
                byte[] SignedData = new byte[fs1.Length];
                fs1.Read(SignedData, 0, (int)fs1.Length);
                fs1.Close();
                //string signed = Encoding.ASCII.GetString(SignedData);
                //SignedData = Encoding.UTF8.GetBytes(signed);

                FileStream fs2 = new FileStream(textBox2.Text, FileMode.Open, FileAccess.Read, FileShare.Read);
                byte[] Public_Key = new byte[fs2.Length];
                fs2.Read(Public_Key, 0, (int)fs2.Length);
                fs2.Close();
                //richTextBox1.Text = Encoding.ASCII.GetString(Public_Key);

                CspParameters cp = new CspParameters();
                cp.KeyContainerName = "信安课设";
                cp.KeyNumber = (int)KeyNumber.Signature;                                           //"1" = Exchanger, 为交换密钥             
                cp.Flags = CspProviderFlags.UseMachineKeyStore;

                RSACryptoServiceProvider RSAalg = new RSACryptoServiceProvider(cp);
                //RSAParameters Key = RSAalg.ExportParameters(true);
                byte[] publickey = RSAalg.ExportCspBlob(false);

                //string public_key = Convert.ToBase64String(Public_Key);
                //string public_key = Encoding.ASCII.GetString(Public_Key);
                string public_key = Convert.ToBase64String(publickey);
                textBox4.Text = public_key;
                
                RSAalg.ImportCspBlob(Convert.FromBase64String(public_key));
                
                
                bool result = RSAalg.VerifyData(DataToVerify, typeof(MD5), SignedData);
                //new RSACryptoServiceProvider().VerifyHash();

                if (result)
                {
                    richTextBox2.Text = "文件签名正确。";
                }

                else
                {
                    richTextBox2.Text = "文件签名错误。";
                }

            }
            catch (Exception x)
            {
                richTextBox2.Text = x.Message;
            }
        }

        //  “退出” 程序
        private void button7_Click(object sender, EventArgs e)
        {
            DialogResult result = MessageBox.Show("确定退出本系统？未保存的数据将会丢失！", "确认退出系统", MessageBoxButtons.OKCancel, MessageBoxIcon.Warning);
            if (result == DialogResult.OK)
            {
                Application.Exit();
            }
        } 
    }
}

补充：.NET技术 ,  C#