Considerations for protecting Email header with S/MIME
draft-melnikov-smime-header-signing-05
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Network Working Group A. Melnikov
Internet-Draft Isode Ltd
Intended status: Informational October 1, 2017
Expires: April 4, 2018
Considerations for protecting Email header with S/MIME
draft-melnikov-smime-header-signing-05
Abstract
This document describes best practices for handling of Email header
protected by S/MIME. It also adds a new Content-Type parameter to
help distinguish an S/MIME protected forwarded message from an S/MIME
construct protecting message header.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on April 4, 2018.
Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
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include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Melnikov Expires April 4, 2018 [Page 1]
Internet-Draft Header protection with S/MIME October 2017
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions Used in This Document . . . . . . . . . . . . . . 3
3. Recommendations for handling of S/MIME protected header . . . 3
4. New Content-Type header field parameter: forwarded . . . . . 4
5. Example message with S/MIME header protection . . . . . . . . 5
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
7. Security Considerations . . . . . . . . . . . . . . . . . . . 5
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
8.1. Normative References . . . . . . . . . . . . . . . . . . 6
8.2. Informative References . . . . . . . . . . . . . . . . . 6
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 7
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
S/MIME [RFC5751] is typically used to protect (sign and/or encrypt)
Email message body parts, but not header of corresponding Email
messages. Header fields may contain confidential information or
information whose validity need protecting from disclosure or
modification. [RFC5751] describes how to protect the Email message
header [RFC5322], by wrapping the message inside a message/rfc822
container [RFC2045]:
In order to protect outer, non-content-related message header
fields (for instance, the "Subject", "To", "From", and "Cc"
fields), the sending client MAY wrap a full MIME message in a
message/rfc822 wrapper in order to apply S/MIME security services
to these header fields. It is up to the receiving client to
decide how to present this "inner" header along with the
unprotected "outer" header.
When an S/MIME message is received, if the top-level protected
MIME entity has a Content-Type of message/rfc822, it can be
assumed that the intent was to provide header protection. This
entity SHOULD be presented as the top-level message, taking into
account header merging issues as previously discussed.
While the above advice helps in protecting message header fields, it
doesn't provide enough guidance on what information should and should
not be included in outer (unprotected) header and how information
from outer and inner headers should be presented to users. This
document describes best UI and other practices for handling of
messages wrapped inside message/rfc822 body parts. The goal of this
document is to improve interoperability and minimize damage caused by
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