{"id":1801,"date":"2011-05-24T10:00:10","date_gmt":"2011-05-24T08:00:10","guid":{"rendered":"http:\/\/www.limilabs.com\/blog\/?p=1801"},"modified":"2016-09-09T11:00:29","modified_gmt":"2016-09-09T09:00:29","slug":"send-signed-email-receive-encrypted","status":"publish","type":"post","link":"https:\/\/www.limilabs.com\/blog\/send-signed-email-receive-encrypted","title":{"rendered":"Send signed email receive encrypted"},"content":{"rendered":"

In this article we’ll show how to create test certificates or use existing certificate, for sending signed emails<\/strong>. Our recipients will use the public key information from the signed email to encrypt emails<\/strong> they’ll be sending to us. Finally we’ll show how to decrypt <\/strong>those emails.<\/p>\n

Create test certificate<\/h2>\n

We’ll use makecert.exe<\/em> tool to create certificate in cer <\/em>format and pvk2pfx.exe<\/em> tool to convert it to pfx <\/em>format:<\/p>\n


\nmakecert.exe -pe -r -sv Test_Keys.pvk -n \"CN=Alice,E=alice2@testdomain.com\" -sky exchange Test.cer
\n<\/code>
\n
\npvk2pfx.exe -pvk Test_Keys.pvk -spc Test.cer -pfx Test.pfx
\n<\/code><\/p>\n

\"\"<\/p>\n

\nIf you use CER or PEM files you can find more information in this article:
\nImporting private\/public keys or certificates in PEM, CER formats<\/a>.\n<\/div>\n

Create S\/MIME signed email<\/h2>\n

Now we’ll create a signed message<\/strong> using Mail.dll. It is a simple task we just need to load certifcate from disk and use SignWith<\/em> method:<\/p>\n

\r\nX509Certificate2 certificate = new X509Certificate2(\r\n    @"c:\\Test.pfx";, \r\n    "", \r\n    X509KeyStorageFlags.PersistKeySet);\r\n\r\nIMail email = Limilabs.Mail.Fluent.Mail.Text("This is a signed message")\r\n    .Subject("This is a signed message")\r\n    .From("alice2@testdomain.com")\r\n    .To("test@testdomain.com")\r\n    .SignWith(certificate)\r\n    .Create();\r\n<\/pre>\n
Send S\/MIME signed email<\/h2>\n
Now we’ll use Smtp <\/em>class to connect and authenticate to our SMTP server and send the email message:<\/p>\n
\r\nusing(Smtp smtp = new Smtp())\r\n{\r\n    smtp.Connect("smtp.server.com");  \/\/ or ConnectSSL for SSL\r\n    smtp.UseBestLogin("user", "password");\r\n \r\n    smtp.SendMessage(email);                     \r\n \r\n    smtp.Close();   \r\n}              \r\n<\/pre>\n
Here you can find more details on sending S\/MIME signed email<\/a>.<\/p>\n
S\/MIME signed email is received<\/h2>\n
Here’s how the recipient will see the message. Please note that we are using self-signed certificates<\/strong> and this is why we are seeing this warning message.<\/p>\n
\"\"<\/a><\/p>\n
Next step for the recipient is to mark received certificate as trusted<\/strong>.<\/p>\n
<\/p>\n
The recipient should then add the certificate to the contact<\/strong> list:<\/p>\n
\"\"<\/a><\/p>\n
As you can see there is a DigitalID <\/strong>assigned to Alice (email sender):<\/p>\n
\"\"<\/a><\/p>\n
S\/MIME encrypted email reply<\/h2>\n
Finally recipient replies to the message marking the new message to be encrypted<\/strong>.<\/p>\n
<\/p>\n
 Receiving S\/MIME encrypted email reply<\/h2>\n
We’ll use IMAP component to download this message<\/a>. You can use IMAP or POP3 components to download it<\/a>.<\/p>\n
In fact we can see that it is encrypted (we are showing raw eml variable here):<\/p>\n
\"\"<\/p>\n
Now we can decrypt the message using the same certificate, we used for signing. Note that we are adding this certificate to SMIMEConfiguration.Certificates<\/em> collection:<\/p>\n
\r\nX509Certificate2 certificate = new X509Certificate2(\r\n    @"c:\\Text.pfx", \r\n    "", \r\n    X509KeyStorageFlags.PersistKeySet);\r\n\r\nusing(Imap imap = new Imap())\r\n{\r\n    imap.Connect("imap.testdomain.com");\r\n    imap.UseBestLogin("alice2@testdomain.com", "password");\r\n\r\n    var eml = imap.GetMessageByNumber(1);\r\n\r\n    MailBuilder builder = new MailBuilder();\r\n    builder.SMIMEConfiguration.Certificates.Add(certificate);\r\n    IMail email = builder.CreateFromEml(eml);\r\n\r\n    Console.WriteLine(email.IsEncrypted);\r\n    Console.WriteLine(email.Html);\r\n    Console.WriteLine(email.Text);\r\n\r\n    imap.Close();\r\n}\r\n<\/pre>\n
\"\"<\/p>\n
You can also find more information about SMIME and Mail.dll here:<\/p>\n