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CipherReference Class

Note: This class is new in the .NET Framework version 2.0.

Represents the <CipherReference> element in XML encryption. This class cannot be inherited.

Namespace: System.Security.Cryptography.Xml
Assembly: System.Security (in system.security.dll)

public sealed class CipherReference : EncryptedReference
public final class CipherReference extends EncryptedReference
public final class CipherReference extends EncryptedReference

This class represents the <CipherReference> element in XML encryption. It identifies a source which, when processed, yields the encrypted data.

The actual encrypted data referenced by the <CipherReference> is obtained by the following process. The <CipherReference> URI property contains a Uniform Resource Identifier (URI) that is dereferenced. If the <CipherReference> element also contains a transform chain, the data resulting from dereferencing the URI is transformed as specified to produce the encrypted data. For example, if the encrypted data is base64-encoded within an XML document, the transforms would specify an XPath expression followed by a base64 decoding so the encrypted data can be extracted.

The syntax of the URI and transforms is similar to that of XML digital signatures. However, in XML digital signatures, both generation and validation processing start with the same source data and perform that transform in the same order. In XML encryption, the decrypting application has only the encrypted data and the specified transforms. The transforms are enumerated in the order necessary to obtain the encrypted data.

Note   By default, you cannot dereference cipher references from documents with unknown sources, such as files from a Web site, because the DocumentEvidence property is null. For example, when you attempt to decrypt a file containing a <CipherReference> element that references a file on the Web, a SecurityException is thrown, even if the request is made by a fully trusted assembly.

If you are sure the documents you are decrypting can be trusted, you can change this behavior for fully trusted applications by using the following code:

        Evidence ev = new Evidence();
        ev.AddHost (new Zone(SecurityZone.MyComputer));
        EncryptedXml exml = new EncryptedXml(doc, ev);

The following code example creates a new instance of CipherReference.

using System;
using System.Security.Cryptography.Xml;
using System.Xml;
using System.IO;

/// This sample used the EncryptedData class to create an encrypted data element
/// and write it to an XML file. It demonstrates the use of CipherReference.
namespace EncryptedDataSample
{
	class Sample1
	{
		[STAThread]
		static void Main(string[] args)
		{
			//Create a URI string.
			String uri = "http://www.woodgrovebank.com/document.xml";
			// Create a Base64 transform. The input content retrieved from the
			// URI should be Base64-decoded before other processing.
			Transform base64 = new XmlDsigBase64Transform();
			//Create a transform chain and add the transform to it.
			TransformChain tc = new TransformChain();
			tc.Add(base64);
			//Create <CipherReference> information.
			CipherReference reference = new CipherReference(uri, tc);

			// Create a new CipherData object using the CipherReference information.
			// Note that you cannot assign both a CipherReference and a CipherValue
			// to a CipherData object.
			CipherData cd = new CipherData(reference);

			// Create a new EncryptedData object.
			EncryptedData ed = new EncryptedData();

			//Add an encryption method to the object.
			ed.Id = "ED";
			ed.EncryptionMethod = new EncryptionMethod("http://www.w3.org/2001/04/xmlenc#aes128-cbc");
			ed.CipherData = cd;

			//Add key information to the object.
			KeyInfo ki = new KeyInfo();
			ki.AddClause(new KeyInfoRetrievalMethod("#EK", "http://www.w3.org/2001/04/xmlenc#EncryptedKey"));
			ed.KeyInfo = ki;

			// Create new XML document and put encrypted data into it.
			XmlDocument doc = new XmlDocument();
			XmlElement encryptionPropertyElement = (XmlElement)doc.CreateElement("EncryptionProperty", EncryptedXml.XmlEncNamespaceUrl);
			EncryptionProperty ep = new EncryptionProperty(encryptionPropertyElement);
			ed.AddProperty(ep);

			// Output the resulting XML information into a file.
			try
			{
				string path = @"c:\test\MyTest.xml";

				File.WriteAllText(path, ed.GetXml().OuterXml);
			}
			catch (IOException e)
			{
				Console.WriteLine("File IO error. {0}", e);
			}

		}
	}
}

package EncryptedDataSample;

import System.*;
import System.Security.Cryptography.Xml.*;
import System.Xml.*;
import System.IO.*;

/// This sample used the EncryptedData class to create an encrypted data element
/// and write it to an XML file. It demonstrates the use of CipherReference.
class Sample1
{
    /** @attribute STAThread()
     */
    public static void main(String[] args)
    {
        //Create a URI string.
        String uri = "http://www.woodgrovebank.com/document.xml";
        // Create a Base64 transform. The input content retrieved from the
        // URI should be Base64-decoded before other processing.
        Transform base64 = new XmlDsigBase64Transform();
        //Create a transform chain and add the transform to it.
        TransformChain tc = new TransformChain();
        tc.Add(base64);
        //Create <CipherReference> information.
        CipherReference reference = new CipherReference(uri, tc);
        // Create a new CipherData object using the CipherReference information.
        // Note that you cannot assign both a CipherReference and a CipherValue
        // to a CipherData object.
        CipherData cd = new CipherData(reference);
        // Create a new EncryptedData object.
        EncryptedData ed = new EncryptedData();
        //Add an encryption method to the object.
        ed.set_Id("ED");
        ed.set_EncryptionMethod(new EncryptionMethod(
            "http://www.w3.org/2001/04/xmlenc#aes128-cbc"));
        ed.set_CipherData(cd);
        //Add key information to the object.
        KeyInfo ki = new KeyInfo();
        ki.AddClause(new KeyInfoRetrievalMethod("#EK", 
            "http://www.w3.org/2001/04/xmlenc#EncryptedKey"));
        ed.set_KeyInfo(ki);
        // Create new XML document and put encrypted data into it.
        XmlDocument doc = new XmlDocument();
        XmlElement encryptionPropertyElement = (XmlElement)doc.CreateElement(
            "EncryptionProperty", EncryptedXml.XmlEncNamespaceUrl);
        EncryptionProperty ep = 
            new EncryptionProperty(encryptionPropertyElement);
        ed.AddProperty(ep);
        // Output the resulting XML information into a file.
        try {
            String path = "c:\\test\\MyTest.xml";

            File.WriteAllText(path, ed.GetXml().get_OuterXml());
        }
        catch (IOException e) {
            Console.WriteLine("File IO error. {0}", e);
        }
    } //main
} //Sample1

System.Object
   System.Security.Cryptography.Xml.EncryptedReference
    System.Security.Cryptography.Xml.CipherReference

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

Windows 98, Windows 2000 SP4, Windows Millennium Edition, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see System Requirements.

.NET Framework

Supported in: 2.0

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