MIME Parts and Message Source for a Digitally Signed Message

SUMMARY

The following example describes what the MIME parts and message source will look like for a signed message.

   X-Mailer: Microsoft Outlook Express 4.71.0729.0

   From: "Ryan LaBrie" <ryanl@microsoft.com>

   To: "steven@somecompany.com" <steven@somecompany.com>

   Subject: signed message

   Date: Wed, 30 Apr 1997 20:37:03 -0700

   X-Priority: 3

   X-MSMail-Priority: Normal

   MIME-Version: 1.0

   Content-Type: multipart/signed;

   boundary="----=_NextPart_000_01BC55A9.8FA8A740";

   micalg=sha1;

   protocol=application/x-pkcs7-signature

   X-MimeOLE: Produced By Microsoft MimeOLE Engine V4.71.0728.0

   NOTE - This is a multi-part message in MIME format.

   ------=_NextPart_000_01BC55A9.8FA8A740

   Content-Type: multipart/alternative;

   boundary="----=_NextPart_001_01BC55A9.8FAA2DE0"

   ------=_NextPart_001_01BC55A9.8FAA2DE0

   Content-Type: text/plain;

   charset="iso-8859-1"

   Content-Transfer-Encoding: quoted-printable

   NOTE - This is a clear signed message.

   ------=_NextPart_001_01BC55A9.8FAA2DE0

   Content-Type: text/html;

   charset="iso-8859-1"

   Content-Transfer-Encoding: quoted-printable

   <!DOCTYPE HTML PUBLIC "-//W3C//DTD W3 HTML 3.2//EN"><HTML>

   <HEAD>

   <META HTTP-EQUIV=3D"Content-Type" CONTENT=3D"text/html; =

   charset=3DUS-ASCII">

   <META content=3D'"Trident 4.71.0729.0"' name=3DGENERATOR>

   </HEAD>

   <BODY>

   <P><FONT SIZE=3D2 FACE=3D"Arial">This is a clear signed message =

   hopefully...</FONT></P>

   </BODY>

   </HTML>

   ------=_NextPart_001_01BC55A9.8FAA2DE0--

   ------=_NextPart_000_01BC55A9.8FA8A740

   Content-Type: application/x-pkcs7-signature;

   name="smime.p7s"

   Content-Transfer-Encoding: base64

   Content-Disposition: attachment;

   filename="smime.p7s"

   MIIGTAYJKoZIhvcNAQcCoIIGPTCCBjkCAQExCzAJBgUrDgMCGgUAMAsGCSqGSIb3DQEHAaCC
   BTsw

   ggU3MIIEoKADAgECAhBO9j8bsMhfLRsKSiktdU5hMA0GCSqGSIb3DQEBBAUAMGIxETAPBgNV
   BAcT

   CEludGVybmV0MRcwFQYDVQQKEw5WZXJpU2lnbiwgSW5jLjE0MDIGA1UECxMrVmVyaVNpZ24g
   Q2xh

   c3MgMSBDQSAtIEluZGl2aWR1YWwgU3Vic2NyaWJlcjAeFw05NzAyMjAwMDAwMDBaFw05ODAy
   MjAy

   . (lots of content deleted)

   ------=_NextPart_000_01BC55A9.8FA8A740--
				

The last part of the message is the signed hash of the message and is sent using the content-transfer-encoding type of Base64 which will allow the transmission of 8-bit data encoded in a 7-bit format. Hence, it is quite unreadable. This part of the message is listed as an attachment with the filename smime.p7s. Mail clients that are not S/MIME aware will display this file as an attachment. If the message is received by an S/MIME aware client, there will not be a visible attachment. In addition, in the above message, the certificate was included and would be available for importing into the Windows Address Book.