回答使用“7”个参数调用“CryptUnProtectData”时发生异常:“无法在 DLL“crypt32.dll”中找到名为“CryptUnProtectData”的入口点。

using System;
using System.Runtime.InteropServices;
using System.Text;
using System.Security;

namespace CryptProtection
{
 [Serializable()]
 public sealed class DataProtection
 {
 [Flags()]
 public enum CryptProtectPromptFlags
 {
 CRYPTPROTECT_PROMPT_ON_UNPROTECT = 0x01,
 CRYPTPROTECT_PROMPT_ON_PROTECT = 0x02,
 CRYPTPROTECT_PROMPT_RESERVED = 0x04,
 CRYPTPROTECT_PROMPT_STRONG = 0x08,
 CRYPTPROTECT_PROMPT_REQUIRE_STRONG = 0x10
 }

 [Flags()]
 public enum CryptProtectDataFlags
 {
 CRYPTPROTECT_UI_FORBIDDEN = 0x01,
 CRYPTPROTECT_LOCAL_MACHINE = 0x04,
 CRYPTPROTECT_CRED_SYNC = 0x08,
 CRYPTPROTECT_AUDIT = 0x10,
 CRYPTPROTECT_NO_RECOVERY = 0x20,
 CRYPTPROTECT_VERIFY_PROTECTION = 0x40,
 CRYPTPROTECT_CRED_REGENERATE = 0x80
 }

 #region 加密数据
 public static string ProtectData(string data, string name)
 {
 return ProtectData(data, name, 
 CryptProtectDataFlags.CRYPTPROTECT_UI_FORBIDDEN | CryptProtectDataFlags.CRYPTPROTECT_LOCAL_MACHINE);
 }

 public static byte[] ProtectData(byte[] data, string name)
 {
 return ProtectData(data, name, 
 CryptProtectDataFlags.CRYPTPROTECT_UI_FORBIDDEN | CryptProtectDataFlags.CRYPTPROTECT_LOCAL_MACHINE);
 }

 public static string ProtectData(string data, string name, CryptProtectDataFlags flags)
 {
 byte[] dataIn = Encoding.Unicode.GetBytes(data);
 byte[] dataOut = ProtectData(dataIn, name, flags);

 if (dataOut != null)
 return (Convert.ToBase64String(dataOut));
 else
 return null;
 }

 /// <summary>
 /// 加密数据
 /// </summary>
 /// <param name="data">要加密的明文数据</param>
 /// <param name="name">有意义的描述，此描述会加到加密后的数据中</param>
 /// <param name="dwFlags">flags的位标志</param>
 /// <returns></returns>
 private static byte[] ProtectData(byte[] data, string name, CryptProtectDataFlags dwFlags)
 {
 byte[] cipherText = null;

 // copy data into unmanaged memory
 //DATA_BLOB结构，用于CryptProtectData参数
 DPAPI.DATA_BLOB din = new DPAPI.DATA_BLOB();
 din.cbData = data.Length;

 //Marshal类的作用：提供了一个方法集，这些方法用于分配非托管内存、复制非托管内存块、将托管类型转换为非托管类型，
 //此外还提供了在与非托管代码交互时使用的其他杂项方法。 
 //为din.pbData分配内存
 din.pbData = Marshal.AllocHGlobal(din.cbData);

 //InPtr结构:用于表示指针或句柄的平台特定类型
 //分配内存错误，抛出内存不足异常
 //IntPtr.Zero:一个只读字段，代表已初始化为零的指针或句柄
 if (din.pbData.Equals(IntPtr.Zero))
 throw new OutOfMemoryException("Unable to allocate memory for buffer.");

 //将data数组中的数据复制到pbData内存指针中
 Marshal.Copy(data, 0, din.pbData, din.cbData);

 //声明DPAPI类的DATA_BLOB公共结构类型
 DPAPI.DATA_BLOB dout = new DPAPI.DATA_BLOB();

 try
 {
 //加密数据
 bool cryptoRetval = DPAPI.CryptProtectData(ref din, name, IntPtr.Zero, IntPtr.Zero, IntPtr.Zero, dwFlags, ref dout);

 //判断加密是否成功
 if (cryptoRetval) // 成功
 {
 int startIndex = 0;
 //分配cipherText数据元素大小为dout.cbData
 cipherText = new byte[dout.cbData];
 //从dout.pbData内存指针指向的内容拷贝到byte数组cipherText中
 Marshal.Copy(dout.pbData, cipherText, startIndex, dout.cbData);
 //从内存中释放指针指向的数据I
 DPAPI.LocalFree(dout.pbData);
 }
 else
 {
 //加密失败，获得错误信息
 int errCode = Marshal.GetLastWin32Error();
 StringBuilder buffer = new StringBuilder(256);
 //显示错误信息
 Win32Error.FormatMessage(Win32Error.FormatMessageFlags.FORMAT_MESSAGE_FROM_SYSTEM, IntPtr.Zero, errCode, 0, buffer, buffer.Capacity, IntPtr.Zero);
 }
 }
 finally
 {
 // 如果din.pbData非空，则释放din.pbData使用的内存
 if (!din.pbData.Equals(IntPtr.Zero))
 Marshal.FreeHGlobal(din.pbData);
 }

 //返回加密后的数据
 return cipherText;
 }
 #endregion


 #region 解密数据
 public static byte[] UnprotectData(byte[] data)
 {
 return UnprotectData(data, CryptProtectDataFlags.CRYPTPROTECT_UI_FORBIDDEN);
 }

 public static string UnprotectData(string data)
 {
 byte[] dataIn = Convert.FromBase64String(data);
 byte[] dataOut = UnprotectData(dataIn);

 if (dataOut != null)
 return Encoding.Unicode.GetString(dataOut);
 else
 return null;
 }

 internal static byte[] UnprotectData(byte[] data, CryptProtectDataFlags dwFlags)
 {
 byte[] clearText = null;

 // copy data into unmanaged memory
 DPAPI.DATA_BLOB din = new DPAPI.DATA_BLOB();
 din.cbData = data.Length;
 din.pbData = Marshal.AllocHGlobal(din.cbData);

 if (din.pbData.Equals(IntPtr.Zero))
 throw new OutOfMemoryException("Unable to allocate memory for buffer.");

 Marshal.Copy(data, 0, din.pbData, din.cbData);

 DPAPI.DATA_BLOB dout = new DPAPI.DATA_BLOB();

 try
 {
 bool cryptoRetval = DPAPI.CryptUnprotectData(ref din, null, IntPtr.Zero, IntPtr.Zero, IntPtr.Zero, dwFlags, ref dout);

 if (cryptoRetval) // ERROR_SUCCESS?
 {
 clearText = new byte[dout.cbData];
 Marshal.Copy(dout.pbData, clearText, 0, dout.cbData);
 DPAPI.LocalFree(dout.pbData);
 }
 else
 {
 int errCode = Marshal.GetLastWin32Error();
 StringBuilder buffer = new StringBuilder(256);
 Win32Error.FormatMessage(Win32Error.FormatMessageFlags.FORMAT_MESSAGE_FROM_SYSTEM, IntPtr.Zero, errCode, 0, buffer, buffer.Capacity, IntPtr.Zero);
 }
 }
 finally
 {
 // free the allocated memory in use
 if (!din.pbData.Equals(IntPtr.Zero))
 Marshal.FreeHGlobal(din.pbData);
 }

 return clearText;
 }
 #endregion

 internal static void InitPromptstruct(ref DPAPI.CRYPTPROTECT_PROMPTSTRUCT ps)
 {
 ps.cbSize = Marshal.SizeOf(typeof(DPAPI.CRYPTPROTECT_PROMPTSTRUCT));
 ps.dwPromptFlags = 0;
 ps.hwndApp = IntPtr.Zero;
 ps.szPrompt = null;
 }
 }

 //允许托管代码不经过堆栈步即调入非托管代码
 [SuppressUnmanagedCodeSecurityAttribute()]
 internal class DPAPI
 {
 [DllImport("crypt32")]
 public static extern bool CryptProtectData(ref DATA_BLOB dataIn, string szDataDescr, IntPtr optionalEntropy, IntPtr pvReserved,
 IntPtr pPromptStruct, DataProtection.CryptProtectDataFlags dwFlags, ref DATA_BLOB pDataOut);

 [DllImport("crypt32")]
 public static extern bool CryptUnprotectData(ref DATA_BLOB dataIn, StringBuilder ppszDataDescr, IntPtr optionalEntropy,
 IntPtr pvReserved, IntPtr pPromptStruct, DataProtection.CryptProtectDataFlags dwFlags, ref DATA_BLOB pDataOut);

 [DllImport("Kernel32.dll")]
 public static extern IntPtr LocalFree(IntPtr hMem);

 [StructLayout(LayoutKind.Sequential)]
 public struct DATA_BLOB
 {
 public int cbData;
 public IntPtr pbData;
 }

 [StructLayout(LayoutKind.Sequential)]
 public struct CRYPTPROTECT_PROMPTSTRUCT
 {
 public int cbSize; // = Marshal.SizeOf(typeof(CRYPTPROTECT_PROMPTSTRUCT))
 public int dwPromptFlags; // = 0
 public IntPtr hwndApp; // = IntPtr.Zero
 public string szPrompt; // = null
 }
 }


 internal class Win32Error
 {
 [Flags()]
 public enum FormatMessageFlags : int
 {
 FORMAT_MESSAGE_ALLOCATE_BUFFER = 0x0100,
 FORMAT_MESSAGE_IGNORE_INSERTS = 0x0200,
 FORMAT_MESSAGE_FROM_STRING = 0x0400,
 FORMAT_MESSAGE_FROM_HMODULE = 0x0800,
 FORMAT_MESSAGE_FROM_SYSTEM = 0x1000,
 FORMAT_MESSAGE_ARGUMENT_ARRAY = 0x2000,
 FORMAT_MESSAGE_MAX_WIDTH_MASK = 0xFF,
 }

 [DllImport("Kernel32.dll")]
 public static extern int FormatMessage(FormatMessageFlags flags, IntPtr source, int messageId, int languageId , 
 StringBuilder buffer, int size, IntPtr arguments);
 }
}

$data=@"

替换成上面的C# 代码

"@

Add-Type -TypeDefinition $data

$testData = [CryptProtection.DataProtection]::ProtectData('www.pstips.net','pstips')
"加密后"
$testData

"解密后"
[CryptProtection.DataProtection]::UnprotectData($testData)

输出：

加密后
AQAAANCMnd8BFdERjHoAwE/Cl+sBAAAAHCA+2Qsa00mrt4OKgAOKAgQAAAAIAAAAcHN0aXBzAAAQZgAAAAEAACAAAACC5/9fonbW0Nb4XIUHGOjLMIiwYLBlg7YFC1khtRGKKAAAAAAO
gAAAAAIAACAAAAB9zy/wXSpCByQoHhJA99WfMRMocB/y/tNl1LiLbddhPyAAAAAJG014TsJXo4DxpKA5ZbbUXHYx0+5wcsTvlplrpuIRC0AAAAB8683YcDVqH4lgS9MceOhYAEpR9nI5
Xw72iU755cF3iP3XivkZ7GPEQj+vxKHpHC9jX37puENQ9D34/iyvRtIZ
解密后
www.pstips.net

本答案C# 引用自：C#中利用DPAPI加密解密数据