It was a request of one of my client to send the mail as encrypted so that this kept secure while sending to customers. So after a search I found
Jason Niver's code to be very handy to use. So I am sharing this will all so next time it becomes little bit easy to get.
using System;
using System.Text;
using System.Net.Mail;
using System.IO;
using
System.Security.Cryptography.Pkcs;
using
System.Security.Cryptography.X509Certificates;
namespace CommonUtilities
{
//requires reference to System.Security
class EmailUtil
{
public static void SendEncryptedEmail(string[] to, string from, string subject, string body, string[] attachments)
{
MailMessage message = new MailMessage();
message.From = new MailAddress(from);
message.Subject = subject;
if (attachments != null &&
attachments.Length > 0)
{
StringBuilder buffer = new StringBuilder();
buffer.Append("MIME-Version:
1.0\r\n");
buffer.Append("Content-Type:
multipart/mixed; boundary=unique-boundary-1\r\n");
buffer.Append("\r\n");
buffer.Append("This is a
multi-part message in MIME format.\r\n");
buffer.Append("--unique-boundary-1\r\n");
buffer.Append("Content-Type:
text/plain\r\n"); //could use text/html
as well here if you want a html message
buffer.Append("Content-Transfer-Encoding:
7Bit\r\n\r\n");
buffer.Append(body);
if (!body.EndsWith("\r\n"))
buffer.Append("\r\n");
buffer.Append("\r\n\r\n");
foreach (string filename in attachments)
{
FileInfo fileInfo = new FileInfo(filename);
buffer.Append("--unique-boundary-1\r\n");
buffer.Append("Content-Type:
application/octet-stream; file=" + fileInfo.Name + "\r\n");
buffer.Append("Content-Transfer-Encoding:
base64\r\n");
buffer.Append("Content-Disposition:
attachment; filename=" + fileInfo.Name + "\r\n");
buffer.Append("\r\n");
byte[] binaryData = File.ReadAllBytes(filename);
string base64Value = Convert.ToBase64String(binaryData,
0, binaryData.Length);
int position = 0;
while (position <
base64Value.Length)
{
int chunkSize = 100;
if (base64Value.Length -
(position + chunkSize) < 0)
chunkSize =
base64Value.Length - position;
buffer.Append(base64Value.Substring(position, chunkSize));
buffer.Append("\r\n");
position += chunkSize;
}
buffer.Append("\r\n");
}
body = buffer.ToString();
}
else
{
body = "Content-Type:
text/plain\r\nContent-Transfer-Encoding: 7Bit\r\n\r\n" + body;
}
byte[] messageData = Encoding.ASCII.GetBytes(body);
ContentInfo content = new
ContentInfo(messageData);
EnvelopedCms envelopedCms = new
EnvelopedCms(content);
CmsRecipientCollection toCollection
= new
CmsRecipientCollection();
foreach (string address in to)
{
message.To.Add(new
MailAddress(address));
X509Certificate2 certificate = null; //Need to load from
store or from file the client's cert
CmsRecipient recipient = new
CmsRecipient(SubjectIdentifierType.SubjectKeyIdentifier, certificate);
toCollection.Add(recipient);
}
envelopedCms.Encrypt(toCollection);
byte[] encryptedBytes = envelopedCms.Encode();
//add digital signature:
SignedCms signedCms = new SignedCms(new
ContentInfo(encryptedBytes));
X509Certificate2 signerCertificate
= null; //Need to load from
store or from file the signer's cert
CmsSigner signer = new
CmsSigner(SubjectIdentifierType.SubjectKeyIdentifier, signerCertificate);
signedCms.ComputeSignature(signer);
encryptedBytes =
signedCms.Encode();
//end digital signature section
MemoryStream stream = new MemoryStream(encryptedBytes);
AlternateView view = new AlternateView(stream,
"application/pkcs7-mime;
smime-type=signed-data;name=smime.p7m");
message.AlternateViews.Add(view);
SmtpClient client = new SmtpClient("your.smtp.mailhost");
//add authentication info if required by your
smtp server etc...
//client.Credentials =
CredentialCache.DefaultCredentials;
client.Send(message);
}
}
}
Now its time to install the
certificate, for this go with the bellow codes.
using
System.Security.Cryptography.X509Certificates;
private X509Certificate
GetCertificate()
{
X509Store store = new
X509Store(StoreName.My, StoreLocation.LocalMachine);
store.Open(OpenFlags.ReadOnly);
X509Certificate2Collection certs =
store.Certificates.Find(X509FindType.FindBySerialNumber, “123456”, true);
store.Close();
return certs[0];
}
Sources:
1. Sending encrypted mail
2. Using certificates from the Windows certificate store
