using System;

using System.Security;

using System.Runtime.InteropServices;

using System.Reflection;

​

public class Program

{

    public static void Main()

    {

        SecureString secure = new SecureString();

        Extensions.AppendString(secure, "Hello world");

        // Or secure.Append("Hello world");

        IntPtr pSecuredString = GetInternalBuffer(secure);

        Console.WriteLine("Address of Secured SecureString: 0x{0:X16}", pSecuredString.ToInt64());

        string strSecuredString = Marshal.PtrToStringUni(pSecuredString);

        Console.WriteLine("Value of Secured SecureString  : {0}", strSecuredString);

        IntPtr pSecureString = Marshal.SecureStringToGlobalAllocUnicode(secure);

        Console.WriteLine("Address of SecureString: 0x{0:X16}", pSecureString.ToInt64());

        string strSecureString = Marshal.PtrToStringUni(pSecureString);

        Console.WriteLine("Value of SecureString  : {0}", strSecureString);

        Marshal.ZeroFreeGlobalAllocUnicode(pSecuredString);

        Marshal.ZeroFreeGlobalAllocUnicode(pSecureString);

    }

    static readonly Type SecureStringType = typeof(SecureString);

    public static IntPtr GetInternalBuffer(SecureString s) {

        FieldInfo   field           = SecureStringType.GetField("m_buffer", BindingFlags.NonPublic | BindingFlags.Instance);

        SafeHandle  handle          = (SafeHandle) field.GetValue(s);

        IntPtr      internalBuffer  = handle.DangerousGetHandle();

        return internalBuffer;

    }

}

​

public static class Extensions {

    public static void Append(this SecureString s, string str) {

        foreach ( char ch in str ) 

            s.AppendChar(ch);

    }

    public static void AppendString(SecureString s, string str) {

        Append(s, str);

    }

}