HOW TO：使用對稱金鑰解密 XML 項目
您可以使用 System.Security.Cryptography.Xml 命名空間中的類別，加密 XML 文件中的項目。 XML 加密能讓您儲存或傳輸機密的 XML，而不需擔心資料會輕易遭到讀取。 這個程式碼範例會使用 Advanced Encryption Standard (AES) 演算法 (也稱為 Rijndael 演算法) 解密 XML 項目。
如需有關如何使用這個程序來加密 XML 項目的詳細資訊，請參閱 HOW TO：使用對稱金鑰加密 XML 項目。
使用對稱演算法 (如 AES) 加密 XML 資料時，您必須使用同一個金鑰來加密和解密 XML 資料。 這個程序中的範例假設加密的 XML 是使用相同的金鑰加密，且加密和解密的兩方在使用的演算法和金鑰方面已取得共識。 這個範例並未在加密的 XML 內儲存或加密 AES 金鑰。
這個範例適用於當單一應用程式需要根據儲存在記憶體中的工作階段金鑰來加密資料，或是根據從密碼衍生的密碼編譯強式金鑰來加密資料的情況。 在兩個以上的應用程式都需要共用加密 XML 資料的情況下，您可以考慮使用以非對稱演算法或 X.509 憑證為基礎的加密配置。
若要使用對稱金鑰解密 XML 項目
使用 HOW TO：使用對稱金鑰加密 XML 項目中所描述的技巧，以先前產生的金鑰加密 XML 項目。
在加密的 XML 所在的 XmlDocument 物件中尋找 <EncryptedData> 項目 (由 XML 加密標準定義)，並建立新的 XmlElement 物件來表示該項目。
Dim encryptedElement As XmlElement = Doc.GetElementsByTagName("EncryptedData")(0)XmlElement encryptedElement = Doc.GetElementsByTagName("EncryptedData")[0] as XmlElement;從先前建立的 XmlElement 物件載入未經處理的 XML 資料，以建立 EncryptedData 物件。
Dim edElement As New EncryptedData() edElement.LoadXml(encryptedElement)EncryptedData edElement = new EncryptedData(); edElement.LoadXml(encryptedElement);建立新的 EncryptedXml 物件，使用此物件並以與加密時所用相同的金鑰來解密 XML 資料。
Dim exml As New EncryptedXml() ' Decrypt the element using the symmetric key. Dim rgbOutput As Byte() = exml.DecryptData(edElement, Alg)EncryptedXml exml = new EncryptedXml(); // Decrypt the element using the symmetric key. byte[] rgbOutput = exml.DecryptData(edElement, Alg);以剛解密的純文字項目取代 XML 文件中的加密項目。
exml.ReplaceData(encryptedElement, rgbOutput)exml.ReplaceData(encryptedElement, rgbOutput);
範例
Imports System
Imports System.Xml
Imports System.Security.Cryptography
Imports System.Security.Cryptography.Xml
Module Program
Sub Main(ByVal args() As String)
Dim key As RijndaelManaged = Nothing
Try
' Create a new Rijndael key.
key = New RijndaelManaged()
' Load an XML document.
Dim xmlDoc As New XmlDocument()
xmlDoc.PreserveWhitespace = True
xmlDoc.Load("test.xml")
' Encrypt the "creditcard" element.
Encrypt(xmlDoc, "creditcard", key)
Console.WriteLine("The element was encrypted")
Console.WriteLine(xmlDoc.InnerXml)
Decrypt(xmlDoc, key)
Console.WriteLine("The element was decrypted")
Console.WriteLine(xmlDoc.InnerXml)
Catch e As Exception
Console.WriteLine(e.Message)
Finally
' Clear the key.
If Not (key Is Nothing) Then
key.Clear()
End If
End Try
End Sub
Sub Encrypt(ByVal Doc As XmlDocument, ByVal ElementName As String, ByVal Key As SymmetricAlgorithm)
' Check the arguments.
If Doc Is Nothing Then
Throw New ArgumentNullException("Doc")
End If
If ElementName Is Nothing Then
Throw New ArgumentNullException("ElementToEncrypt")
End If
If Key Is Nothing Then
Throw New ArgumentNullException("Alg")
End If
''''''''''''''''''''''''''''''''''''''''''''''''''
' Find the specified element in the XmlDocument
' object and create a new XmlElemnt object.
''''''''''''''''''''''''''''''''''''''''''''''''''
Dim elementToEncrypt As XmlElement = Doc.GetElementsByTagName(ElementName)(0)
' Throw an XmlException if the element was not found.
If elementToEncrypt Is Nothing Then
Throw New XmlException("The specified element was not found")
End If
''''''''''''''''''''''''''''''''''''''''''''''''''
' Create a new instance of the EncryptedXml class
' and use it to encrypt the XmlElement with the
' symmetric key.
''''''''''''''''''''''''''''''''''''''''''''''''''
Dim eXml As New EncryptedXml()
Dim encryptedElement As Byte() = eXml.EncryptData(elementToEncrypt, Key, False)
''''''''''''''''''''''''''''''''''''''''''''''''''
' Construct an EncryptedData object and populate
' it with the desired encryption information.
''''''''''''''''''''''''''''''''''''''''''''''''''
Dim edElement As New EncryptedData()
edElement.Type = EncryptedXml.XmlEncElementUrl
' Create an EncryptionMethod element so that the
' receiver knows which algorithm to use for decryption.
' Determine what kind of algorithm is being used and
' supply the appropriate URL to the EncryptionMethod element.
Dim encryptionMethod As String = Nothing
If TypeOf Key Is TripleDES Then
encryptionMethod = EncryptedXml.XmlEncTripleDESUrl
ElseIf TypeOf Key Is DES Then
encryptionMethod = EncryptedXml.XmlEncDESUrl
End If
If TypeOf Key Is Rijndael Then
Select Case Key.KeySize
Case 128
encryptionMethod = EncryptedXml.XmlEncAES128Url
Case 192
encryptionMethod = EncryptedXml.XmlEncAES192Url
Case 256
encryptionMethod = EncryptedXml.XmlEncAES256Url
End Select
Else
' Throw an exception if the transform is not in the previous categories
Throw New CryptographicException("The specified algorithm is not supported for XML Encryption.")
End If
edElement.EncryptionMethod = New EncryptionMethod(encryptionMethod)
' Add the encrypted element data to the
' EncryptedData object.
edElement.CipherData.CipherValue = encryptedElement
''''''''''''''''''''''''''''''''''''''''''''''''''
' Replace the element from the original XmlDocument
' object with the EncryptedData element.
''''''''''''''''''''''''''''''''''''''''''''''''''
EncryptedXml.ReplaceElement(elementToEncrypt, edElement, False)
End Sub 'Encrypt
Sub Decrypt(ByVal Doc As XmlDocument, ByVal Alg As SymmetricAlgorithm)
' Check the arguments.
If Doc Is Nothing Then
Throw New ArgumentNullException("Doc")
End If
If Alg Is Nothing Then
Throw New ArgumentNullException("Alg")
End If
' Find the EncryptedData element in the XmlDocument.
Dim encryptedElement As XmlElement = Doc.GetElementsByTagName("EncryptedData")(0)
' If the EncryptedData element was not found, throw an exception.
If encryptedElement Is Nothing Then
Throw New XmlException("The EncryptedData element was not found.")
End If
' Create an EncryptedData object and populate it.
Dim edElement As New EncryptedData()
edElement.LoadXml(encryptedElement)
' Create a new EncryptedXml object.
Dim exml As New EncryptedXml()
' Decrypt the element using the symmetric key.
Dim rgbOutput As Byte() = exml.DecryptData(edElement, Alg)
' Replace the encryptedData element with the plaintext XML element.
exml.ReplaceData(encryptedElement, rgbOutput)
End Sub
End Module
using System;
using System.Xml;
using System.Security.Cryptography;
using System.Security.Cryptography.Xml;
namespace CSCrypto
{
class Program
{
static void Main(string[] args)
{
RijndaelManaged key = null;
try
{
// Create a new Rijndael key.
key = new RijndaelManaged();
// Load an XML document.
XmlDocument xmlDoc = new XmlDocument();
xmlDoc.PreserveWhitespace = true;
xmlDoc.Load("test.xml");
// Encrypt the "creditcard" element.
Encrypt(xmlDoc, "creditcard", key);
Console.WriteLine("The element was encrypted");
Console.WriteLine(xmlDoc.InnerXml);
Decrypt(xmlDoc, key);
Console.WriteLine("The element was decrypted");
Console.WriteLine(xmlDoc.InnerXml);
}
catch (Exception e)
{
Console.WriteLine(e.Message);
}
finally
{
// Clear the key.
if (key != null)
{
key.Clear();
}
}
}
public static void Encrypt(XmlDocument Doc, string ElementName, SymmetricAlgorithm Key)
{
// Check the arguments.
if (Doc == null)
throw new ArgumentNullException("Doc");
if (ElementName == null)
throw new ArgumentNullException("ElementToEncrypt");
if (Key == null)
throw new ArgumentNullException("Alg");
////////////////////////////////////////////////
// Find the specified element in the XmlDocument
// object and create a new XmlElemnt object.
////////////////////////////////////////////////
XmlElement elementToEncrypt = Doc.GetElementsByTagName(ElementName)[0] as XmlElement;
// Throw an XmlException if the element was not found.
if (elementToEncrypt == null)
{
throw new XmlException("The specified element was not found");
}
//////////////////////////////////////////////////
// Create a new instance of the EncryptedXml class
// and use it to encrypt the XmlElement with the
// symmetric key.
//////////////////////////////////////////////////
EncryptedXml eXml = new EncryptedXml();
byte[] encryptedElement = eXml.EncryptData(elementToEncrypt, Key, false);
////////////////////////////////////////////////
// Construct an EncryptedData object and populate
// it with the desired encryption information.
////////////////////////////////////////////////
EncryptedData edElement = new EncryptedData();
edElement.Type = EncryptedXml.XmlEncElementUrl;
// Create an EncryptionMethod element so that the
// receiver knows which algorithm to use for decryption.
// Determine what kind of algorithm is being used and
// supply the appropriate URL to the EncryptionMethod element.
string encryptionMethod = null;
if (Key is TripleDES)
{
encryptionMethod = EncryptedXml.XmlEncTripleDESUrl;
}
else if (Key is DES)
{
encryptionMethod = EncryptedXml.XmlEncDESUrl;
}
if (Key is Rijndael)
{
switch (Key.KeySize)
{
case 128:
encryptionMethod = EncryptedXml.XmlEncAES128Url;
break;
case 192:
encryptionMethod = EncryptedXml.XmlEncAES192Url;
break;
case 256:
encryptionMethod = EncryptedXml.XmlEncAES256Url;
break;
}
}
else
{
// Throw an exception if the transform is not in the previous categories
throw new CryptographicException("The specified algorithm is not supported for XML Encryption.");
}
edElement.EncryptionMethod = new EncryptionMethod(encryptionMethod);
// Add the encrypted element data to the
// EncryptedData object.
edElement.CipherData.CipherValue = encryptedElement;
////////////////////////////////////////////////////
// Replace the element from the original XmlDocument
// object with the EncryptedData element.
////////////////////////////////////////////////////
EncryptedXml.ReplaceElement(elementToEncrypt, edElement, false);
}
public static void Decrypt(XmlDocument Doc, SymmetricAlgorithm Alg)
{
// Check the arguments.
if (Doc == null)
throw new ArgumentNullException("Doc");
if (Alg == null)
throw new ArgumentNullException("Alg");
// Find the EncryptedData element in the XmlDocument.
XmlElement encryptedElement = Doc.GetElementsByTagName("EncryptedData")[0] as XmlElement;
// If the EncryptedData element was not found, throw an exception.
if (encryptedElement == null)
{
throw new XmlException("The EncryptedData element was not found.");
}
// Create an EncryptedData object and populate it.
EncryptedData edElement = new EncryptedData();
edElement.LoadXml(encryptedElement);
// Create a new EncryptedXml object.
EncryptedXml exml = new EncryptedXml();
// Decrypt the element using the symmetric key.
byte[] rgbOutput = exml.DecryptData(edElement, Alg);
// Replace the encryptedData element with the plaintext XML element.
exml.ReplaceData(encryptedElement, rgbOutput);
}
}
}
這個範例假設，在已編譯程式的相同目錄中，有名為 "test.xml" 的檔案。 它也會假設，"test.xml" 包含 "creditcard" 項目。 您可以將下列 XML 放在名為 test.xml 的檔案中，與這個範例搭配使用。
<root>
<creditcard>
<number>19834209</number>
<expiry>02/02/2002</expiry>
</creditcard>
</root>
編譯程式碼
若要編譯這個範例，您需要包含對 System.Security.dll 的參考。
包含下列命名空間：System.Xml、System.Security.Cryptography 和 System.Security.Cryptography.Xml。
安全性
請勿以純文字格式儲存密碼編譯金鑰，也不要將金鑰以純文字形式在電腦之間傳輸。
當您完成使用對稱密碼編譯金鑰時，請將每個位元組設為零，或呼叫 Managed 加密類別的 Clear 方法，從記憶體清除密碼編譯金鑰。
請參閱
工作
參考
System.Security.Cryptography.Xml