C# SecureString 问题

Question

有没有什么方法可以在不包含安全性的情况下获取 SecureString 的值？例如，在下面的代码中，只要您执行 PtrToStringBSTR，字符串就不再安全，因为字符串是不可变的，并且垃圾回收对于字符串来说是不确定的。

IntPtr ptr = Marshal.SecureStringToBSTR(SecureString object);
string value = Marshal.PtrToStringBSTR(ptr);

如果有办法获取非托管 BSTR 字符串的 char[] 或 byte[] 会怎么样？这是否意味着垃圾收集更可预测(因为您将使用 char[] 或 byte[] 而不是字符串？这个假设是否正确，如果是这样，您将如何取回 char[] 或 byte[]？

Answer 1

这是我专门为此目的编写的一个类。它是完全、100% 防黑客的吗？不 - 要使应用程序 100% 安全，您几乎无能为力，但是如果您需要将 SecureString 转换为 String<，则此类会尽可能地保护您自己.

下面是你如何使用这个类:

using(SecureStringToStringMarshaler sm = new SecureStringToStringMarshaler(secureString))
{
    // Use sm.String here.  While in the 'using' block, the string is accessible
    // but pinned in memory.  When the 'using' block terminates, the string is zeroed
    // out for security, and garbage collected as usual.
}

这是类

/// Copyright (C) 2010 Douglas Day
/// All rights reserved.
/// MIT-licensed: http://www.opensource.org/licenses/mit-license.php

using System;
using System.Collections.Generic;
using System.Text;
using System.Security;
using System.Runtime.InteropServices;
using System.Runtime.CompilerServices;

namespace DDay.Base
{
    public class SecureStringToStringMarshaler : IDisposable
    {
        #region Private Fields

        private string _String;
        private SecureString _SecureString;
        private GCHandle _GCH;

        #endregion

        #region Public Properties

        public SecureString SecureString
        {
            get { return _SecureString; }
            set
            {
                _SecureString = value;
                UpdateStringValue();
            }
        }

        public string String
        {
            get { return _String; }
            protected set { _String = value; }
        } 

        #endregion

        #region Constructors

        public SecureStringToStringMarshaler()
        {
        }

        public SecureStringToStringMarshaler(SecureString ss)        
        {
            SecureString = ss;
        }

        #endregion

        #region Private Methods

        void UpdateStringValue()
        {
            Deallocate();

            unsafe
            {
                if (SecureString != null)
                {
                    int length = SecureString.Length;
                    String = new string('\0', length);

                    _GCH = new GCHandle();

                    // Create a CER (Contrained Execution Region)
                    RuntimeHelpers.PrepareConstrainedRegions();
                    try { }
                    finally
                    {
                        // Pin our string, disallowing the garbage collector from
                        // moving it around.
                        _GCH = GCHandle.Alloc(String, GCHandleType.Pinned);
                    }

                    IntPtr stringPtr = IntPtr.Zero;
                    RuntimeHelpers.ExecuteCodeWithGuaranteedCleanup(
                        delegate
                        {
                            // Create a CER (Contrained Execution Region)
                            RuntimeHelpers.PrepareConstrainedRegions();
                            try { }
                            finally
                            {
                                stringPtr = Marshal.SecureStringToBSTR(SecureString);
                            }

                            // Copy the SecureString content to our pinned string
                            char* pString = (char*)stringPtr;
                            char* pInsecureString = (char*)_GCH.AddrOfPinnedObject();
                            for (int index = 0; index < length; index++)
                            {
                                pInsecureString[index] = pString[index];
                            }
                        },
                        delegate
                        {
                            if (stringPtr != IntPtr.Zero)
                            {
                                // Free the SecureString BSTR that was generated
                                Marshal.ZeroFreeBSTR(stringPtr);
                            }
                        },
                        null);
                }
            }
        }

        void Deallocate()
        {            
            if (_GCH.IsAllocated)
            {
                unsafe
                {
                    // Determine the length of the string
                    int length = String.Length;

                    // Zero each character of the string.
                    char* pInsecureString = (char*)_GCH.AddrOfPinnedObject();
                    for (int index = 0; index < length; index++)
                    {
                        pInsecureString[index] = '\0';
                    }

                    // Free the handle so the garbage collector
                    // can dispose of it properly.
                    _GCH.Free();
                }
            }
        } 

        #endregion

        #region IDisposable Members

        public void Dispose()
        {
            Deallocate();
        }

        #endregion
    }
}

此代码要求您可以编译不安全 代码，但它的效果非常好。

问候，

-道格