How to use EWS API for reading SMIME email message

What is SMIME – http://technet.microsoft.com/en-us/library/aa995740(v=exchg.65).aspx 

class Program
{
static ExchangeService exService;

static void Main(string[] args)
{
try
{
exService = new ExchangeService(ExchangeVersion.Exchange2010_SP1);
exService.UseDefaultCredentials = true;
exService.AutodiscoverUrl(“user@Contoso.com”, RedirectionCallback);

Console.WriteLine(“Connected(Autodiscovered EWS Endpoint)- ” + exService.Url);

//find the trace log dumped in debug\log.txt
exService.TraceEnabled = true;
exService.TraceListener = new TraceListener();
exService.TraceEnablePrettyPrinting = true;

Console.WriteLine(“Getting inbox items..”);
byte[] data = GetInboxMailItems();

if (data == null)
{
Console.WriteLine(“No Mails retreived “);
Console.ReadKey();
return;
}
//
byte[] resultObject= DecryptToFile(data);

if(resultObject==null)
{
Console.WriteLine(“No object retrieved from Decrypt. somthing wrong in this method”);

}
else
{
string uniqueFname = Path.GetRandomFileName()+”.eml”;
Console.WriteLine(@”Decrypted EML file dumped here — c:\temp\” + uniqueFname);

//Find the decrypted file here
//Load this file in Outlook for testing.
File.WriteAllBytes(@”c:\temp\” + uniqueFname, resultObject);
}

//write the decrypted content to a file – mail item .eml
Console.WriteLine(“Press any key to exit..”);
Console.ReadKey();
}
catch (Exception ex)
{
Console.WriteLine(“Error while initializing..” + ex.ToString());
}
}

/// <summary>
///
/// </summary>
private static byte[] GetInboxMailItems()
{
byte[] data = null;

//Get inbox unread mails (have a mail ready for decrypt which is signed & decrypt)
Folder inbox = Folder.Bind(exService, WellKnownFolderName.Inbox);
SearchFilter sf = new SearchFilter.SearchFilterCollection(LogicalOperator.And, new SearchFilter.IsEqualTo(EmailMessageSchema.IsRead, false));

ItemView view = new ItemView(1);

FindItemsResults<Item> findResults = exService.FindItems(WellKnownFolderName.Inbox, sf, view);

//Have atleast 1 unread ‘encrypted,signed’ mail for this testing
if (findResults.TotalCount == 0)
{
return data;
Console.WriteLine(“No Mails retreived”);
}

//Loop through the items and do whatever is required.
foreach (Item item in findResults)
{
//Load the mail item
PropertySet ps = new PropertySet(BasePropertySet.FirstClassProperties, ItemSchema.Attachments);
item.Load(ps);

foreach (Microsoft.Exchange.WebServices.Data.Attachment attach in item.Attachments)
{
// find the encrypted mails attachment- in general body and any mail content for encrypted mail would be bundled as smime.p7m file in mailstore
if (attach.Name == “smime.p7m”)
{
Console.WriteLine(“Process smime.p7m file”);
FileAttachment fileAttachment = (FileAttachment)attach;
MemoryStream stream = new MemoryStream();
fileAttachment.Load(stream);
StreamReader stReader = new StreamReader(stream);
stream.Seek(0, SeekOrigin.Begin);
data = stream.GetBuffer();

return data;
}
}
}
return data;
}

/// <summary>
///
/// </summary>
/// <param name=”data”></param>
private static byte[] DecryptToFile(byte[] data)
{
byte[] resultObject = null;

try
{
EnvelopedCms envelopObj = new EnvelopedCms();
envelopObj.Decode(data);

Console.WriteLine(“Encryption Algorithm: Name={0}”, envelopObj.ContentEncryptionAlgorithm.Oid.FriendlyName);
Console.WriteLine(“Key length={0}”, envelopObj.ContentEncryptionAlgorithm.KeyLength);
Console.WriteLine(“Recipients ({0})”, envelopObj.RecipientInfos.Count);

foreach (RecipientInfo r in envelopObj.RecipientInfos)
{
Console.WriteLine(” Encrypted key={0}”, BitConverter.ToString(r.EncryptedKey));
Console.WriteLine(” Encryption alg={0}”, r.KeyEncryptionAlgorithm.Oid.FriendlyName);

if (r.RecipientIdentifier.Type == SubjectIdentifierType.IssuerAndSerialNumber)
{
X509IssuerSerial xi = (X509IssuerSerial)r.RecipientIdentifier.Value;
Console.WriteLine(” Issuer={0}”, xi.IssuerName);
Console.WriteLine(” SerialNumber={0}”, xi.SerialNumber);
}
else
{
Console.WriteLine(” SubjectKeyInfo={0}”, r.RecipientIdentifier.Value);
}
}

Console.WriteLine(“Certificates ({0})”, envelopObj.Certificates.Count);

foreach (X509Certificate2 cert in envelopObj.Certificates)
{
Console.WriteLine(“Subject={0}”, cert.SubjectName);
}

Console.WriteLine(“Unprotected Attributes ({0})”, envelopObj.UnprotectedAttributes.Count);

foreach (CryptographicAttributeObject obj in envelopObj.UnprotectedAttributes)
{
Console.WriteLine(obj.Oid.FriendlyName);
}

envelopObj.Decrypt();
Console.WriteLine(“Success. Decrypted… !!”);
resultObject = envelopObj.ContentInfo.Content;

return resultObject; ;
}
catch (Exception ex)
{
Console.WriteLine(ex.ToString());
}
return resultObject;
}

/// <summary>
///
/// </summary>
/// <param name=”url”></param>
/// <returns></returns>
static bool RedirectionCallback(string url)
{
// Return true if the URL is an HTTPS URL.
return url.ToLower().StartsWith(“https://&#8221;);
}
}

/// <summary>
///
/// </summary>
public class TraceListener : ITraceListener
{
#region ITraceListener Members

public void Trace(string traceType, string traceMessage)
{
CreateXMLTextFile(traceType + ” — ” + traceMessage.ToString());
}

#endregion

private void CreateXMLTextFile(string traceContent)
{
string strPath = System.AppDomain.CurrentDomain.BaseDirectory;
strPath = strPath + “\\Log.txt”;
System.IO.FileStream fs;
if (System.IO.File.Exists(strPath) == false)
{
fs = System.IO.File.Create(strPath);
}
else
{
fs = System.IO.File.OpenWrite(strPath);
}

fs.Close();

// Create an instance of StreamWriter to write text to a file.
System.IO.StreamWriter sw = System.IO.File.AppendText(strPath);
sw.WriteLine(System.DateTime.Now.ToString() + “: ” + traceContent);
sw.Close();

}
}