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CipherReference Class

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

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

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

[HostProtectionAttribute(SecurityAction.LinkDemand, MayLeakOnAbort = true)]
public sealed class CipherReference : EncryptedReference

The CipherReference type exposes the following members.

  NameDescription
Public methodCipherReference()Initializes a new instance of the CipherReference class.
Public methodCipherReference(String)Initializes a new instance of the CipherReference class using the specified Uniform Resource Identifier (URI).
Public methodCipherReference(String, TransformChain)Initializes a new instance of the CipherReference class using the specified Uniform Resource Identifier (URI) and transform chain information.
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  NameDescription
Protected propertyCacheValidGets a value that indicates whether the cache is valid. (Inherited from EncryptedReference.)
Protected propertyReferenceTypeGets or sets a reference type. (Inherited from EncryptedReference.)
Public propertyTransformChainGets or sets the transform chain of an EncryptedReference object. (Inherited from EncryptedReference.)
Public propertyUriGets or sets the Uniform Resource Identifier (URI) of an EncryptedReference object. (Inherited from EncryptedReference.)
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  NameDescription
Public methodAddTransformAdds a Transform object to the current transform chain of an EncryptedReference object. (Inherited from EncryptedReference.)
Public methodEquals(Object)Determines whether the specified Object is equal to the current Object. (Inherited from Object.)
Protected methodFinalizeAllows an object to try to free resources and perform other cleanup operations before it is reclaimed by garbage collection. (Inherited from Object.)
Public methodGetHashCodeServes as a hash function for a particular type. (Inherited from Object.)
Public methodGetTypeGets the Type of the current instance. (Inherited from Object.)
Public methodGetXmlReturns the XML representation of a CipherReference object. (Overrides EncryptedReference.GetXml().)
Public methodLoadXmlLoads XML information into the <CipherReference> element in XML encryption. (Overrides EncryptedReference.LoadXml(XmlElement).)
Protected methodMemberwiseCloneCreates a shallow copy of the current Object. (Inherited from Object.)
Public methodToStringReturns a string that represents the current object. (Inherited from Object.)
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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);
NoteNote

The HostProtectionAttribute attribute applied to this type or member has the following Resources property value: MayLeakOnAbort. The HostProtectionAttribute does not affect desktop applications (which are typically started by double-clicking an icon, typing a command, or entering a URL in a browser). For more information, see the HostProtectionAttribute class or SQL Server Programming and Host Protection Attributes.

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);
			}

		}
	}
}


.NET Framework

Supported in: 4, 3.5, 3.0, 2.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

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

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

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