DataServiceContextEx_ReadingEntity changes not affecting underlying DataSet. Full code sample included

Question

I have the following code on Azure that should work on your local machine if you change the 2 certificate thumbprint references: http://azuretableencrypt.codeplex.com/SourceControl/list/changesets#

 

Here is the actual file that does the decryption

http://azuretableencrypt.codeplex.com/SourceControl/changeset/view/77778#1551445

 

When I debug I see that the event fires for encryption, and works.  I see that decryption doesn't.  I've been staring at this code too long to see the issue; would appreciate it if someone can tell me how to get ASP.NET to display the decrypted version of the data.

Answer 1

Have you verified with Fiddler and direct observation using, for example, Cloud Storage Studio that the entity was uploaded with the expected properties and values?

Answer 2

I can see the encrypted values as expected when deployed to the cloud and checked the contents using https://www.myazurestorage.com 

 

The only issue is that upon decryption, I don't see the decrypted value. I see gibberish.  However when I set a breakpoint I see that I'm decoding the content correctly.

Answer 3

Here is the actual code that is not working.  See the section that says "decrypt this property"?  When I put a breakpoint there, the code does decrypt the date and it replaces the encrypted value with unencrypted value (for display purposes).

 

However this change doesn't affect the dataset.  Can anyone explain why?

 

 

public class MessageDataServiceContext  : TableServiceContext
  {
    public MessageDataServiceContext(string baseAddress, StorageCredentials credentials)
      : base(baseAddress, credentials)
    {
      this.WritingEntity += new EventHandler<ReadingWritingEntityEventArgs>(DataServiceContextEx_WritingEntity);
      this.ReadingEntity += new EventHandler<ReadingWritingEntityEventArgs>(DataServiceContextEx_ReadingEntity);

       this.azCrypto = new EncryptDecrypt.AzureTableCrypto(baseAddress, credentials);

      // Todo: CHANGE THIS: Replace this certificate hash with your certificate. You can use your SSL key for simplicity
       this.azCrypto.LoadCertificateByThumbprint("‎1e c3 26 00 da 34 05 c9 44 c7 75 18 84 c7 8b a7 e4 f4 ed 8b");
    }

    AzureTableCrypto azCrypto = null;

    void DataServiceContextEx_ReadingEntity(object sender, ReadingWritingEntityEventArgs e)
    {
      // Todo: Next Version: support more than one version of Key
      int KeyVersion = 0;

      // e.Data gives you the XElement for the Serialization of the Entity 
      //Using XLinq , you can add/Remove properties to the element Payload 
      XName xnEntityProperties = XName.Get("properties", e.Data.GetNamespaceOfPrefix("m").NamespaceName);
      XElement xePayload = null;
      foreach (PropertyInfo property in e.Entity.GetType().GetProperties())
      {
        object[] transparentEncryptAttributes = property.GetCustomAttributes(typeof(EncryptAttribute), false);
        if (transparentEncryptAttributes.Length > 0)
        {
          if (xePayload == null)
          {
            // Null exception happens here
            xePayload = e.Data.Descendants().Where<XElement>(xe => xe.Name == xnEntityProperties).First<XElement>();
          }
          // Try to get the namespace, may be null if ATOM format
          var dNamespacePrefix = e.Data.GetNamespaceOfPrefix("d");
          if (dNamespacePrefix != null)
          {
            if (!String.IsNullOrEmpty(dNamespacePrefix.NamespaceName))
            {
              //The XName of the property we are going to encrypt from the payload
              XName xnProperty = XName.Get(property.Name, dNamespacePrefix.NamespaceName);
              //Get the Property of the entity you want to encrypt on the server
              XElement xeDecryptThisProperty = xePayload
                      .Descendants()
                      .Where<XElement>(xe => xe.Name == xnProperty)
                      .First<XElement>();

              //Decrypt this property 
              xeDecryptThisProperty.Value = azCrypto.DecryptString(xeDecryptThisProperty.Value,0);
            }
          }
          else
	        {
            // The object didn't have the encrypt property set
	        }
        }
      }

<span style="font-family:Consolas,'Courier New',Courier,monospace; font-size:x-small">--}</span>

 

Answer 4

Hello Chris,

I downloaded and debugged you project. When the following line in Default.aspx.cs page is called:

this.messageList.DataSource = context.Messages;

The actual raw xml data returned is:

<entry m:etag="W/&quot;datetime'2011-05-13T15%3A41%3A28.847Z'&quot;" xmlns="http://www.w3.org/2005/Atom" xmlns:m="http://schemas.microsoft.com/ado/2007/08/dataservices/metadata">
  <id>http://127.0.0.1:10002/devstoreaccount1/Messages(PartitionKey='a',RowKey='12520969707112181959_81962fd7-db9c-452e-8a96-d3969fe3aeaf')</id>
  <title type="text"></title>
  <updated>2011-05-13T15:42:11Z</updated>
  <author>
    <name />
  </author>
  <link rel="edit" title="Messages" href="Messages(PartitionKey='a',RowKey='12520969707112181959_81962fd7-db9c-452e-8a96-d3969fe3aeaf')" />
  <category term="devstoreaccount1.Messages" scheme="http://schemas.microsoft.com/ado/2007/08/dataservices/scheme" />
  <content type="application/xml">
    <m:properties>
      <d:PartitionKey xmlns:d="http://schemas.microsoft.com/ado/2007/08/dataservices">a</d:PartitionKey>
      <d:RowKey xmlns:d="http://schemas.microsoft.com/ado/2007/08/dataservices">12520969707112181959_81962fd7-db9c-452e-8a96-d3969fe3aeaf</d:RowKey>
      <d:Timestamp m:type="Edm.DateTime" xmlns:d="http://schemas.microsoft.com/ado/2007/08/dataservices">2011-05-13T15:41:28.847Z</d:Timestamp>
      <d:Body xmlns:d="http://schemas.microsoft.com/ado/2007/08/dataservices">Pd6x3xTfjBhZWApoYBeXxA==</d:Body>
      <d:Name xmlns:d="http://schemas.microsoft.com/ado/2007/08/dataservices">Anonymous</d:Name>
      <d:BodyCopy xmlns:d="http://schemas.microsoft.com/ado/2007/08/dataservices">hello</d:BodyCopy>
      <d:Seed m:null="true" xmlns:d="http://schemas.microsoft.com/ado/2007/08/dataservices" />
    </m:properties>
  </content>
</entry> 

You can see that there is not a namespace of prefix "d" that in the root element. So for your case,  if (dNamespacePrefix != null) is not passing.

You can either revise the code to deal with that case, or how about using reflection instead of directly processing to the raw xml data?

    void DataServiceContextEx_ReadingEntity(object sender, ReadingWritingEntityEventArgs e)
    {
        int KeyVersion = 0;
         
        foreach (PropertyInfo property in e.Entity.GetType().GetProperties())
        {
            object[] transparentEncryptAttributes = property.GetCustomAttributes(typeof(EncryptAttribute), false);
            if (transparentEncryptAttributes.Length > 0 && property.PropertyType == typeof(string))
            {
                string propertyValue = (string)property.GetValue(e.Entity, null);
                propertyValue = azCrypto.DecryptString(propertyValue, 0);
                property.SetValue(e.Entity, propertyValue, null);
            }
        }
    }

Thanks,

---

Wengchao Zeng
Please mark the replies as answers if they help or unmark if not.
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Microsoft One Code Framework

Answer 5

However this change doesn't affect the dataset.  Can anyone explain why?

 

public class MessageDataServiceContext : TableServiceContext
 {

 ...

  if (!String.IsNullOrEmpty(dNamespacePrefix.NamespaceName))
  {

  ...
  //Decrypt this property 
  xeDecryptThisProperty.Value = azCrypto.DecryptString(xeDecryptThisProperty.Value,0);
  }
  }
 }

The ReadingEntity event "occurs after entity data has been completely read into the entity object" (from http://msdn.microsoft.com/en-us/library/system.data.services.client.dataservicecontext.readingentity.aspx).

In your code, you are processing the XML input and writing the decrypted value back into the XML. You should write the decrypted value to the entity in e.Data instead.

UPDATED: I meant "You should write the decrypted value to the entity in e.Entity instead".

Answer 6

Looks like you may be on to something with e.Entity.  How should I write the value?  It's an object, and needs to be converted somehow.

Once I cast the object I probably need to reflect and get the dynamic property to be decrypted.

 

Any tips would be welcome....

Answer 7

Chris -

In the blog post I referred to above I have some sample code where I accessed the hydrated object and modified a property.

Answer 8

I hadn't seen Wenchao's reply when I wrote mine, but it looks like the code he wrote might do the trick. Did you try it?

Answer 9

Wenchao Zeng - Thank you so much for your assistance!  I just checked in the working version thanks to you!  (I credited you in code)