Please refer this code

Form

Namespaces

using System.Security.Cryptography;
using System.IO;
using System.Data.SqlClient;
using System.Configuration;

C#

public Form1()
{
    InitializeComponent();
    this.PopulateData();
}
private void PopulateData()
{
    dataGridView1.AutoGenerateColumns = false;
    dataGridView1.ColumnCount = 3;
    dataGridView1.Columns[0].Name = "UserName";
    dataGridView1.Columns[0].HeaderText = "UserName";
    dataGridView1.Columns[0].DataPropertyName = "UserName";

    dataGridView1.Columns[1].HeaderText = "Encrpted Password";
    dataGridView1.Columns[1].Name = "Password";
    dataGridView1.Columns[1].DataPropertyName = "Password";

    dataGridView1.Columns[2].HeaderText = "Decrypted Password";
    dataGridView1.Columns[2].Name = "DecryptedPassword";
    dataGridView1.Columns[2].DataPropertyName = "DecryptedPassword";

           
    string constr = ConfigurationManager.ConnectionStrings["constr"].ConnectionString;
    using (SqlConnection con = new SqlConnection(constr))
    {
        using (SqlCommand cmd = new SqlCommand("SELECT *, '' as DecryptedPassword  FROM tblUsers"))
        {
            using (SqlDataAdapter sda = new SqlDataAdapter())
            {
                DataTable dt = new DataTable();
                cmd.CommandType = CommandType.Text;
                cmd.Connection = con;
                sda.SelectCommand = cmd;
                sda.Fill(dt);
                dataGridView1.DataSource = dt;
                foreach (DataGridViewRow row in dataGridView1.Rows)
                {
                    row.Cells[2].Value = Decrypt(row.Cells[1].Value.ToString());
                }
            }
        }
    }
}

private void btnSave_Click(object sender, EventArgs e)
{
    string constr = ConfigurationManager.ConnectionStrings["constr"].ConnectionString;
    using (SqlConnection con = new SqlConnection(constr))
    {
        using (SqlCommand cmd = new SqlCommand("INSERT INTO tblUsers VALUES(@Username, @Password)"))
        {
            cmd.CommandType = CommandType.Text;
            cmd.Parameters.AddWithValue("@Username", txtUserName.Text.Trim());
            cmd.Parameters.AddWithValue("@Password", Encrypt(txtPassword.Text.Trim()));
            cmd.Connection = con;
            con.Open();
            cmd.ExecuteNonQuery();
            con.Close();
        }
    }
    this.PopulateData();
}
        
private string Encrypt(string clearText)
{
    string EncryptionKey = "MAKV2SPBNI99212";
    byte[] clearBytes = Encoding.Unicode.GetBytes(clearText);
    using (Aes encryptor = Aes.Create())
    {
        Rfc2898DeriveBytes pdb = new Rfc2898DeriveBytes(EncryptionKey, new byte[] { 0x49, 0x76, 0x61, 0x6e, 0x20, 0x4d, 0x65, 0x64, 0x76, 0x65, 0x64, 0x65, 0x76 });
        encryptor.Key = pdb.GetBytes(32);
        encryptor.IV = pdb.GetBytes(16);
        using (MemoryStream ms = new MemoryStream())
        {
            using (CryptoStream cs = new CryptoStream(ms, encryptor.CreateEncryptor(), CryptoStreamMode.Write))
            {
                cs.Write(clearBytes, 0, clearBytes.Length);
                cs.Close();
            }
            clearText = Convert.ToBase64String(ms.ToArray());
        }
    }
    return clearText;
}

private string Decrypt(string cipherText)
{
    string EncryptionKey = "MAKV2SPBNI99212";
    byte[] cipherBytes = Convert.FromBase64String(cipherText);
    using (Aes encryptor = Aes.Create())
    {
        Rfc2898DeriveBytes pdb = new Rfc2898DeriveBytes(EncryptionKey, new byte[] { 0x49, 0x76, 0x61, 0x6e, 0x20, 0x4d, 0x65, 0x64, 0x76, 0x65, 0x64, 0x65, 0x76 });
        encryptor.Key = pdb.GetBytes(32);
        encryptor.IV = pdb.GetBytes(16);
        using (MemoryStream ms = new MemoryStream())
        {
            using (CryptoStream cs = new CryptoStream(ms, encryptor.CreateDecryptor(), CryptoStreamMode.Write))
            {
                cs.Write(cipherBytes, 0, cipherBytes.Length);
                cs.Close();
            }
            cipherText = Encoding.Unicode.GetString(ms.ToArray());
        }
    }
    return cipherText;
}