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2.1.3.1 Clear-Signed Message

  • Article

A clear-signed message in the Internet e-mail message format is a message in which the message's MIME entity has the media type "multipart/signed", as specified in [RFC1847]. Such a MIME entity has two body parts: the first part represents signed message content; the second part contains a message signature, as specified in [RFC5751].

A clear-signed message in Internet e-mail message format is mapped to a Message object with the following structure:

  • The message class, as specified by the PidTagMessageClass property ([MS-OXCMSG] section 2.2.1.3) SHOULD<1>          <2> be set to "IPM.Note.SMIME.MultipartSigned"; otherwise, it MAY<3> be set to "IPM.Note.SMIME".

  • The message body SHOULD be set by promoting a primary message body MIME entity to appropriate properties of a Message object, as specified in [MS-OXCMSG] section 2.2, by adhering to the following requirements:

    • Consider the first body part of a multipart/signed message MIME entity as a complete Internet e-mail message.

    • Apply the heuristics specified in [MS-OXCMAIL] to identify a nested MIME entity as a message body and promote its content according to [MS-OXCMAIL] section 2.1.

  • Message object properties other than the message class (PidTagMessageClass property ([MS-OXCMSG] section 2.2.1.3)) or the message body SHOULD be set as specified in [MS-OXCMAIL] section 2.1 and [MS-OXOMSG] section 2.2.

  • The Message object MUST contain exactly one Attachment object.

    • Attachment object content, stored in the PidTagAttachDataBinary property ([MS-OXPROPS] section 2.589), MUST be set as the entire outer content of a multipart/signed message MIME entity, including a Content-Type header field, as specified in [RFC2045], with the value "multipart/signed" and any original parameters. All other message entity header fields SHOULD be excluded. It is important to preserve the entire original outer content of the first body part within a multipart/signed MIME entity without modification, as it is protected by a message signature in its original form, and any modification will invalidate the message signature. Note that all message header fields that are excluded are normally processed to populate Message object properties, as specified in [MS-OXCMAIL] section 2.1.

    • Other Attachment object properties are to be set as follows:

      • The PidTagAttachMethod property ([MS-OXPROPS] section 2.601) MUST be set to a value of 0x00000001 (binary data attachment, as specified in [MS-OXCMSG] section 2.2.2.9).

      • The PidTagAttachMimeTag property ([MS-OXPROPS] section 2.602) MUST be set to a value of "multipart/signed".

      • The PidTagAttachFilename property ([MS-OXPROPS] section 2.593) either is set to a value of "SMIME.txt" or "SMIME.p7m" or is not set.<4>

      • The PidTagAttachLongFilename property ([MS-OXPROPS] section 2.595) SHOULD<5> be set to a value of "SMIME.p7m".

      • The PidTagDisplayName property ([MS-OXPROPS] section 2.677) SHOULD<6> be set to a value of "SMIME.p7m" by the server. The client does not set this property during conversion.