< draft-luck-lamps-pep-header-protection-02.txt   draft-luck-lamps-pep-header-protection-03.txt >
Network Working Group C. Luck Network Working Group C. Luck
Internet-Draft pEp Foundation Internet-Draft pEp Foundation
Intended status: Informational B. Hoeneisen Intended status: Informational July 05, 2019
Expires: September 27, 2019 Ucom.ch Expires: January 6, 2020
March 26, 2019
pretty Easy privacy (pEp): Header Protection pretty Easy privacy (pEp): Progressive Header Disclosure
draft-luck-lamps-pep-header-protection-02 draft-luck-lamps-pep-header-protection-03
Abstract Abstract
Issues with email header protection in S/MIME have been recently Issues with email header protection in S/MIME have been recently
raised in the IETF LAMPS Working Group. The need for amendments to raised in the IETF LAMPS Working Group. The need for amendments to
the existing specification regarding header protection was expressed. the existing specification regarding header protection was expressed.
The pretty Easy privacy (pEp) implementations currently use a The pretty Easy privacy (pEp) implementations currently use a
mechanism quite similar to the currently standardized message mechanism quite similar to the currently standardized message
wrapping for S/MIME. The main difference is that pEp is using PGP/ wrapping for S/MIME. The main difference is that pEp is using PGP/
MIME instead, and adds space for carrying public keys next to the MIME instead, and adds space for carrying public keys next to the
protected message. protected message.
In LAMPS voices have also been expressed, that whatever mechanism In LAMPS, it has been expressed that whatever mechanism will be
will be chosen, it should not be limited to S/MIME, but also chosen, it should not be limited to S/MIME, but also applicable to
applicable to PGP/MIME. PGP/MIME.
This document aims to contribute to this discussion and share pEp This document aims to contribute to this discussion and share the pEp
implementation experience with email header protection. implementation experience with email header protection.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/. Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on September 27, 2019. This Internet-Draft will expire on January 6, 2020.
Copyright Notice Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terms . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 4
2.1. The OpenPGP Radix-64 . . . . . . . . . . . . . . . . . . 4 1.2. Terms . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1.1. Radix-64 in the Context of MIME Messages . . . . . . 5 2. Message Format for Progressive Header Disclosure . . . . . . 4
3. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 5 2.1. Compatibility . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Interactions . . . . . . . . . . . . . . . . . . . . . . 5 2.2. Inner Message . . . . . . . . . . . . . . . . . . . . . . 5
3.2. Protection Levels . . . . . . . . . . . . . . . . . . . . 6 2.3. Content-Type Parameter "forwarded" . . . . . . . . . . . 5
4. Requirements . . . . . . . . . . . . . . . . . . . . . . . . 7 2.4. Outer Message . . . . . . . . . . . . . . . . . . . . . . 5
4.1. General Requirements . . . . . . . . . . . . . . . . . . 7 2.5. Transport Message . . . . . . . . . . . . . . . . . . . . 8
4.1.1. Sending Side . . . . . . . . . . . . . . . . . . . . 7 2.6. S/MIME Compatibility . . . . . . . . . . . . . . . . . . 9
4.1.2. Receiving Side . . . . . . . . . . . . . . . . . . . 8 3. Candidate Header Fields for Header Protection . . . . . . . . 9
4.2. Additional Requirements for Backward-Compatibility With 4. Stub Outside Headers . . . . . . . . . . . . . . . . . . . . 9
Legacy Clients Unaware of Header Protection . . . . . . . 8 5. Processing Incoming Email under Progressive Header Disclosure 10
4.2.1. Sending side . . . . . . . . . . . . . . . . . . . . 8 5.1. Processing of Signed-only Email . . . . . . . . . . . . . 10
4.2.2. Receiving side . . . . . . . . . . . . . . . . . . . 8 5.2. Incoming Filter Processing . . . . . . . . . . . . . . . 10
4.3. Additional Requirements for Backward-Compatibility with 5.2.1. Staged Filtering of Inbound Messages . . . . . . . . 11
Legacy Header Protection Systems (if supported) . . . . . 8 5.3. Outgoing Filter Processing . . . . . . . . . . . . . . . 11
4.3.1. Sending Side . . . . . . . . . . . . . . . . . . . . 9 6. Security Considerations . . . . . . . . . . . . . . . . . . . 12
4.3.2. Receiving Side . . . . . . . . . . . . . . . . . . . 9 7. Privacy Considerations . . . . . . . . . . . . . . . . . . . 12
5. Message Format for progressive header disclosure . . . . . . 9 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
5.1. Design principles . . . . . . . . . . . . . . . . . . . . 9 9. Implementation Status . . . . . . . . . . . . . . . . . . . . 12
5.2. Compatibility . . . . . . . . . . . . . . . . . . . . . . 10 9.1. Introduction . . . . . . . . . . . . . . . . . . . . . . 12
5.3. Inner message . . . . . . . . . . . . . . . . . . . . . . 11 9.2. Current software implementing pEp . . . . . . . . . . . . 12
5.4. Content-Type property "forwarded" . . . . . . . . . . . . 11 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 13
5.5. Outer message . . . . . . . . . . . . . . . . . . . . . . 12 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 13
5.6. Transport message . . . . . . . . . . . . . . . . . . . . 14 11.1. Normative References . . . . . . . . . . . . . . . . . . 13
5.7. S/MIME Compatibility . . . . . . . . . . . . . . . . . . 15 11.2. Informative References . . . . . . . . . . . . . . . . . 14
6. Candidate Header Fields for Header Protection . . . . . . . . 15 Appendix A. About pEp Design Principles . . . . . . . . . . . . 15
7. Stub Outside Headers . . . . . . . . . . . . . . . . . . . . 15 Appendix B. Document Changelog . . . . . . . . . . . . . . . . . 16
8. Processing Incoming Email under Progressive Header Disclosure 16 Appendix C. Open Issues . . . . . . . . . . . . . . . . . . . . 17
8.1. Resolving Conflicting Protected and Unprotected Header Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 17
Fields . . . . . . . . . . . . . . . . . . . . . . . . . 16
8.2. Processing of Signed-only Email . . . . . . . . . . . . . 16
8.3. Incoming Filter Processing . . . . . . . . . . . . . . . 16
8.3.1. Staged Filtering of Inbound Messages . . . . . . . . 17
8.4. Outgoing Filter Processing . . . . . . . . . . . . . . . 17
9. Security Considerations . . . . . . . . . . . . . . . . . . . 18
10. Implementation Status . . . . . . . . . . . . . . . . . . . . 18
10.1. Introduction . . . . . . . . . . . . . . . . . . . . . . 18
10.2. Current software implementing pEp . . . . . . . . . . . 18
11. Privacy Considerations . . . . . . . . . . . . . . . . . . . 19
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19
13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 19
14. References . . . . . . . . . . . . . . . . . . . . . . . . . 19
14.1. Normative References . . . . . . . . . . . . . . . . . . 19
14.2. Informative References . . . . . . . . . . . . . . . . . 21
Appendix A. Document Changelog . . . . . . . . . . . . . . . . . 21
Appendix B. Open Issues . . . . . . . . . . . . . . . . . . . . 22
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 22
1. Introduction 1. Introduction
A range of protocols for the protection of electronic mail (email) A range of protocols for the protection of electronic mail (email)
exist, which allow to assess the authenticity and integrity of the exist, which allow to assess the authenticity and integrity of the
email headers section or selected header fields from the domain-level email headers section, or selected header fields, but limited to a
perspective, specifically DomainKeys Identified Mail (DKIM) [RFC6376] domain-level perspective. Specifically these are DomainKeys
and Sender Policy Framework (SPF) [RFC7208] and Domain-based Message Identified Mail (DKIM) [RFC6376] and Sender Policy Framework (SPF)
Authentication, Reporting, and Conformance (DMARC) [RFC7489]. These [RFC7208] and Domain-based Message Authentication, Reporting, and
protocols, while essential to responding to a range of attacks on Conformance (DMARC) [RFC7489]. These protocols, while essential to
email, do not offer full end-to-end protection to the headers section responding to a range of attacks on email, do not offer full End-to-
and are not capable of providing privacy for the information End protection to the headers section and are not capable of
contained therein. providing privacy regarding the information represented therein.
The need for means of Data Minimization, which includes data The need for means of Data Minimization, which includes data
spareness and hiding of all information, which technically can be spareness and hiding of all information technically hideable, has
hidden, has grown in importance over the past years. grown in importance over the past years.
A standard for end-to-end protection of the email headers section A standard for End-to-End protection of the email headers section
exists for S/MIME since version 3.1. (cf. [RFC5751] and exists for S/MIME since version 3.1. (cf. [RFC8551]):
[I-D.ietf-lamps-rfc5751-bis]):
In order to protect outer, non-content-related message header In order to protect outer, non-content-related message header
fields (for instance, the "Subject", "To", "From", and "Cc" fields (for instance, the "Subject", "To", "From", and "Cc"
fields), the sending client MAY wrap a full MIME message in a fields), the sending client MAY wrap a full MIME message in a
message/rfc822 wrapper in order to apply S/MIME security services message/rfc822 wrapper in order to apply S/MIME security services
to these header fields. to these header fields.
No mechanism for header protection has been standardized for PGP No mechanism for header protection has been standardized for
(Pretty Good Privacy) yet. [PGPMIME] yet.
End-to-end protection for the email headers section is currently not End-to-End protection for the email headers section is currently not
widely implemented - neither for messages protected by means of widely implemented - neither for messages protected by means of
S/MIME nor PGP. At least two variants of header protection are known S/MIME nor PGP/MIME. At least two variants of header protection are
to be implemented. A recently submitted Internet-Draft known to be implemented. A recently submitted Internet-Draft
[I-D.melnikov-lamps-header-protection] discusses the two variants and [I-D.melnikov-lamps-header-protection] discusses the two variants and
the challenges with header protection for S/MIME. The two variants the challenges with header protection for S/MIME. The two variants
are referred to as: are referred to as:
o Option 1: Memory Hole o Option 1: Memory Hole
o Option 2: Wrapping with message/rfc822 or message/global o Option 2: Wrapping with message/rfc822 or message/global
pEp (pretty Easy privacy) [I-D.birk-pep] for email pEp (pretty Easy privacy) [I-D.birk-pep] for email
[I-D.marques-pep-email] already implements an option quite similar to [I-D.marques-pep-email] already implements an option quite similar to
Option 2, adapting the S/MIME standards to PGP/MIME (cf. Section 5, Option 2, adapting the S/MIME standards to PGP/MIME (cf. Section 2,
ff.). Existing implementations of pEp have also added inbound ff.). Existing implementations of pEp have also added inbound
support for "Memory Hole" referred to above as Option 1, thus being support for "Memory Hole" referred to above as Option 1, thus being
able to study the differences and the implementator's challenges. able to study the differences and the implementator's challenges.
pEp now also supports the "forwarded=no" attribute proposed in
[I-D.melnikov-lamps-header-protection], and further described in
Section 2.3.
Interoperability and implementation symmetry between PGP/MIME and Interoperability and implementation symmetry between PGP/MIME and
S/MIME is planned by pEp, but still in an early stage of development. S/MIME is planned by pEp, but still in an early stage of development.
This document lists generic use cases (Section 3) and requirements This document describes Progressive Header Disclosure as implemented
for header protection (Section 4) and describes progressive header in the "pEp message format version 2". This format inherently offers
disclosure as implemented in the "pEp message format version 2". header protection as a side effect, but is only intended for use only
This format inherently offers header protection, and may be with signed-and-encrypted messages. The feature of protecting
implemented independently by mail user agents otherwise not headers may be used independently by mail user agents otherwise not
conforming to pEp standards (Section 5, ff.). wanting to conform to pEp standards (Section 2, ff.).
2. Terms 1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. document are to be interpreted as described in [RFC2119].
o Man-in-the-middle attack (MITM): cf. [RFC4949] 1.2. Terms
2.1. The OpenPGP Radix-64
In the examples following in this section, it is a common pattern to
have a MIME encoded mail containing ("wrapping") another signed and
eventually encrypted mail. Such enclosed mails are encoded following
the OpenPGP standard, which specifies an encoding called "Radix-64",
which is 7-bit transport-encoding compatible by design.
The Radix-64 consists of a begin and an end Armor Header Line, a
stream of base64-encoded data limited to 78 characters per line plus
<CR><LF>, and an encoded CRC-24 value.
The following is an example, with some similar lines of base64 output
replaced with ellipsis:
-----BEGIN PGP MESSAGE-----
hQIMAwusnBHN80H+AQ//cJLQLOl+6hOofKEkQJeu0wedmwt+TkzPx/sCUQ80dzLv
...
j/ES8ndDBftM5mZLzFQ2VatqB9G9cqCgiOVFs6jfTI13nPfLit9IPWRavcVIMdwt
Xd9bdvHx/ReenAk/
=7WaL
-----END PGP MESSAGE-----
To make the examples look more compact and relevant, the above will
be replaced symbolically by:
[[----- OpenPGP Radix-64 Block -----]]
2.1.1. Radix-64 in the Context of MIME Messages
Note that OpenPGP and MIME specifications overlap when a Radix-64
immediately precedes a MIME boundary. The <CR><LF> sequence
immediately preceding a MIME boundary delimiter line is considered to
be part of the delimiter in [RFC2046], 5.1. And in OpenPGP, line
endings are considered a part of the Armor Header Line for the
purposes of determining the content they delimit in [RFC4880], 6.2.
Keeping an empty line between the end Armor Header Line and the MIME
boundary line is suggested.
3. Use Cases
In the following, we show the generic use cases that need to be
addressed independently of whether S/MIME, PGP/MIME or any other
technology is used for which Header Protection (HP) is to be applied
to.
3.1. Interactions
The main interaction case for Header Protection (HP) is:
1) Both peers (sending and receiving side) fully support HP
For backward compatibility of legacy clients - unaware of any HP -
the following intermediate interactions need to be considered as
well:
2) The sending side fully supports HP, while the receiving side does
not support any HP
3) The sending side does not support any HP, while the receiving
side fully supports HP (trivial case)
4) Neither the sending side nor the receiving side supports any HP
(trivial case)
The following intermediate use cases may need to be considered as
well for backward compatibility with legacy HP systems, such as
S/MIME since version 3.1 (cf. [RFC5751] and
[I-D.ietf-lamps-rfc5751-bis]), in the following designated as legacy
HP:
5) The sending side fully supports HP, while the receiving side
supports legacy HP only
6) The sending side supports legacy HP only, while the receiving side
fully supports HP
7) Both peers (sending and receiving side) support legacy HP only
8) The sending side supports legacy HP only, while the receiving side
does not support any HP
9) The sending side does not support any HP, while the receiving side
supports legacy HP only (trivial case)
Note: It is to be decided whether to ensure legacy HP systems do not
conflict with any new solution for HP at all or whether (and to which
degree) backward compatibility to legacy HP systems shall be
maintained.
3.2. Protection Levels
The following protection levels need to be considered:
a) signature and encryption
b) signature only
c) encryption only [[ TODO: verify whether relevant ]]
4. Requirements
In the following a list of requirements that need to be addressed
independently of whether S/MIME, PGP/MIME or any other technology is
used to apply HP to.
4.1. General Requirements
This subsection is listing the requirements to address use case 1)
(cf. Section 3.1).
G1: Define the format for HP for all protection levels. This includes
MIME structure, Content-Type (including charset and name),
Content-Disposition (including filename), and
Content-Transfer-Encoding.
G2: Define how a public key should be included.
G3: To foster wide implementation of the new solution, it shall be
easily implementable. Unless needed for maximizing protection and
privacy, existing implementations shall not require substantial
changes in the existing code base. In particular also MIME
libraries widely used shall not need to be changed to comply with
the new mechanism for HP.
G4: Ensure that man-in-the-middle attack (MITM) cf. {{RFC4949}}, in
particular downgrade attacks, are mitigated as good as possible.
4.1.1. Sending Side
GS1: Determine which Header Fields (HFs) should or must be protected
at least for signed only email.
GS2: Determine which HFs should or must be sent in clear of an
encrypted email.
GS3: Determine which HF should not or must not be included in the
visible header (for transport) of an encrypted email, with the
default being that whatever is not needed from GS2 is not put
into the unencrypted transport headers, thus fulfilling data
minimization requirements (including data spareness and hiding
of all information that technically can be hidden).
GS4: Determine which HF to not to include to any HP part (e.g. Bcc).
4.1.2. Receiving Side
GR1: Determine how HF should be displayed to the user in case of
conflicting information between the protected and unprotected
headers.
GR2: Ensure that man-in-the-middle attack (MITM) cf. {{RFC4949}}, in
particular downgrade attacks, can be detected.
4.2. Additional Requirements for Backward-Compatibility With Legacy
Clients Unaware of Header Protection
This sub-section addresses the use cases 2) - 4) (cf. Section 3.1)
B1: Depending on the solution, define a means to distinguish between
forwarded messages and encapsulated messages using new HP
mechanism.
4.2.1. Sending side
BS1: Define how full HP support can be indicated to outgoing
messages.
BS2: Define how full HP support of the receiver can be detected or
guessed.
BS3: Ensure a HP unaware receiving side easily can display the
"Subject" HF to the user.
4.2.2. Receiving side
BR1: Define how full HP support can be detected in incoming messages.
4.3. Additional Requirements for Backward-Compatibility with Legacy
Header Protection Systems (if supported)
This sub-section addresses the use cases 5) - 9) (cf. Section 3.1).
LS1: Depending on the solution, define a means to distinguish between
forwarded messages, legacy encapsulated messages, and
encapsulated messages using new HP mechanism.
LS2: The solution should be backward compatible to existing solutions
and aim to minimize the implementation effort to include support
for existing solutions.
4.3.1. Sending Side
LSS1: Determine how legacy HP support can be indicated to outgoing
messages.
LSS2: Determine how legacy HP support of the receiver can be detected
or guessed.
4.3.2. Receiving Side
LSR1: Determine how legacy HP support can be detected in incoming
messages.
5. Message Format for progressive header disclosure
5.1. Design principles
pretty Easy privacy (pEp) is working on bringing state-of-the-art
automatic cryptography known from areas like TLS to electronic mail
(email) communication. pEp is determined to evolve the existing
standards as fundamentally and comprehensively as needed to gain easy
implementation and integration, and for easy use for regular Internet
users. pEp for email wants to attaining to good security practice
while still retaining backward compatibility for implementations
widespread.
To provide the required stability as a foundation for good security
practice, pEp for email defines a fixed MIME structure for its
innermost message structure, so to remove most attack vectors which
have permitted the numerous EFAIL vulnerabilities. (TBD: ref)
Security comes just next after privacy in pEp, for which reason the
application of signatures without encryption to messages in transit
is not considered purposeful. pEp for email herein referenced, and
further described in [I-D.marques-pep-email], either expects to
transfer messages in cleartext without signature or encryption, or
transfer them encrypted and with enclosed signature and necessary
public keys so that replies can be immediately upgraded to encrypted
messages.
The pEp message format is equivalent to the S/MIME standard in
ensuring header protection, in that the whole message is protected
instead, by wrapping it and providing cryptographic services to the
whole original message. The pEp message format is different compared
to the S/MIME standard in that the pEp protocols propose
opportunistic end-to-end security and signature, by allowing the
transport of the necessary public key material along with the
original messages.
For the purpose of allowing the insertion of such public keys, the
root entity of the protected message is thus nested once more into an
additional multipart/mixed MIME entity. The current pEp proposal is
for PGP/MIME, while an extension to S/MIME is next.
pEp's proposal is strict in that it requires that the cryptographic The following terms are defined for the scope of this document:
services applied to the protected message MUST include encryption.
It also mandates a fixed MIME structure for the protected message,
which always MUST include a plaintext and optionally an HTML
representation (if HTML is used) of the same message, and requires
that all other optional elements to be eventually presented as
attachments. Alternatively the whole protected message could
represent in turn a wrapped pEp wrapper, which makes the message
structure fully recursive on purpose (e.g., for the purpose of
anonymization through onion routing).
For the purpose of implementing mixnet routing for email, it is o Man-in-the-middle attack (MITM): cf. [RFC4949]
foreseen to nest pEp messages recursively. A protected message can
in turn contain a protected message due for forwarding. This is for
the purpose to increase privacy and counter the necessary leakage of
plaintext addressing in the envelope of the email.
The recursive nature of the pEp message format allows for the 2. Message Format for Progressive Header Disclosure
implementation of progressive disclosure of the necessary transport
relevant header fields just as-needed to the next mail transport
agents along the transmission path.
5.2. Compatibility 2.1. Compatibility
The pEp message format version 2 is designed such that a receiving The pEp message format version 2 is designed such that a receiving
Mail User Agent (MUA), which is OpenPGP-compliant but not pEp- Mail User Agent (MUA), which is OpenPGP-compliant but not pEp-
compliant, still has built-in capability to properly verify the compliant, still has built-in capability to properly verify the
integrity of the mail, decode it and display all information of the integrity of the mail, decode it and display all information of the
original mail to the user. The recovered protected message is original mail to the user. The recovered protected message is
selfsufficiently described, including all protected header fields. selfsufficiently described, including all protected header fields.
The pEp message format version 2 (as used by all the various pEp The pEp message format version 2 (as used by all the various pEp
implementations, cf. Section 10) is similar to what is standardized implementations, cf. Section 9) is similar to what is standardized
for S/MIME in [RFC5751] and its successor for S/MIME in [RFC8551]:
[I-D.ietf-lamps-rfc5751-bis]:
In order to protect outer, non-content-related message header In order to protect outer, non-content-related message header
fields (for instance, the "Subject", "To", "From", and "Cc" fields (for instance, the "Subject", "To", "From", and "Cc"
fields), the sending client MAY wrap a full MIME message in a fields), the sending client MAY wrap a full MIME message in a
message/rfc822 wrapper in order to apply S/MIME security services message/rfc822 wrapper in order to apply S/MIME security services
to these header fields. It is up to the receiving client to to these header fields. It is up to the receiving client to
decide how to present this "inner" header along with the decide how to present this "inner" header along with the
unprotected "outer" header. unprotected "outer" header.
When an S/MIME message is received, if the top-level protected When an S/MIME message is received, if the top-level protected
MIME entity has a Content-Type of message/rfc822, it can be MIME entity has a Content-Type of message/rfc822, it can be
assumed that the intent was to provide header protection. This assumed that the intent was to provide header protection. This
entity SHOULD be presented as the top-level message, [...]. entity SHOULD be presented as the top-level message, [...].
5.3. Inner message 2.2. Inner Message
*Note*: this section is for your information only. It does not add
requirements for the header protection feature to work.
The pEp message format requires the innermost protected message to The pEp message format requires the innermost protected message to
follow a fixed MIME structure and to consist of exactly one human- follow a fixed MIME structure and to consist of exactly one human-
readable message which is represented in plain or HTML format. Both readable message which is represented in plain or HTML format. Both
plain and html entities MUST represent the same message to the user. plain and html entities MUST represent the same message to the user.
Any attachment to the message must be laid out in a flat list. No Any attachment to the message must be laid out in a flat list. No
additional multipart entities are allowed in the pEp message. additional multipart entities are allowed in the pEp message.
These restrictions permit to build mail user agents which are immune These restrictions permit to build mail user agents which are immune
to the EFAIL attacks. to the EFAIL attacks.
This message is herein further referred to as the "pEp inner This message is herein further referred to as the "pEp inner
message". message".
A mail user agent wanting to follow this standard, SHOULD transform A mail user agent wanting to follow this standard, SHOULD transform
any "original message" into a "pEp inner message" for safe any "original message" into a "pEp inner message" for safe
representation on the receiving side. representation on the receiving side.
5.4. Content-Type property "forwarded" 2.3. Content-Type Parameter "forwarded"
One caveat of the design is that the user interaction with message/ One caveat of the design is that the user interaction with message/
rfc822 entities varies considerably across different mail user rfc822 entities varies considerably across different mail user
agents. No standard is currently available which enables MUAs to agents. No standard is currently available which enables MUAs to
reliably determine whenever a nested message/rfc822 entity is meant reliably determine whenever a nested message/rfc822 entity is meant
to blend the containing message, or if it was effectively intended to to blend the containing message, or if it was effectively intended to
be forwarded as a file document. pEp currently intends to implement be forwarded as a file document. pEp currently implements the
the proposal described by [I-D.melnikov-lamps-header-protection], proposal described by [I-D.melnikov-lamps-header-protection], 3.2,
3.2, which defines a new Content-Type header field parameter with which defines a new Content-Type header field parameter with name
name "forwarded", for the MUA to distinguish between a forwarded "forwarded", for the MUA to distinguish between a forwarded message
message and a nested message for the purpose of header protection, and a nested message for the purpose of header protection, i.e.,
i.e., using "forwarded=no". using "forwarded=no".
5.5. Outer message 2.4. Outer Message
With pEp message format version 2, the pEp standardized message is With pEp message format version 2, the pEp standardized message is
equally wrapped in a message/rfc822 entity, but this time being in equally wrapped in a message/rfc822 entity, but this time being in
turn wrapped in a multipart/mixed entity. The purpose of the turn wrapped in a multipart/mixed entity. The purpose of the
additional nesting is to allow for public keys of the sender to be additional nesting is to allow for public keys of the sender to be
stored alongside the original message while being protected by the stored alongside the original message while being protected by the
same mechanism. same mechanism.
For the case of PGP/MIME, the currently only implemented MIME For the case of PGP/MIME, the currently only implemented MIME
encryption protocol implemented in pEp, the top-level entity called encryption protocol implemented in pEp, the top-level entity called
skipping to change at page 14, line 5 skipping to change at page 8, line 5
Content-Type: application/pgp-keys Content-Type: application/pgp-keys
Content-Disposition: attachment; filename="pEpkey.asc" Content-Disposition: attachment; filename="pEpkey.asc"
-----BEGIN PGP PUBLIC KEY BLOCK----- -----BEGIN PGP PUBLIC KEY BLOCK-----
... ...
-----END PGP PUBLIC KEY BLOCK----- -----END PGP PUBLIC KEY BLOCK-----
--6b8b4567327b23c6643c986966334873-- --6b8b4567327b23c6643c986966334873--
5.6. Transport message 2.5. Transport Message
In pEp message format 2 the "outer message" consists of a full RFC822 In pEp message format 2 the "outer message" consists of a full RFC822
message with body and a minimal set of header fields, just those message with body and a minimal set of header fields, just those
necessary to conform to MIME multipart standards. necessary to conform to MIME multipart standards.
The "outer message" should be encrypted and carry a signature The "outer message" should be encrypted and carry a signature
according to the MIME encryption standards. The resulting message is according to the MIME encryption standards. The resulting message is
the transport message which a root entity of type multipart/ the transport message which a root entity of type multipart/
encrypted. encrypted.
A minimal set of header fields should be set on the "transport A minimal set of header fields should be set on the "transport
message", as to permit delivery, without disclosing private message", as to permit delivery, without disclosing private
information. information.
The structure of the transport message may be altered in-transit, The structure of the transport message may be altered in-transit,
e.g. through mailing list agents, or inspection gateways. e.g. through mailing list agents, or inspection gateways.
Signing and encrypting a message with MIME Security with OpenPGP Signing and encrypting a message with MIME Security with [PGPMIME],
[RFC3156], yields a message with the following complete MIME yields a message with the following complete MIME structure, seen
structure, seen across the encryption layer: across the encryption layer:
= multipart/encrypted; protocol="application/pgp-encrypted"; = multipart/encrypted; protocol="application/pgp-encrypted";
+ application/pgp-encrypted [ Version: 1 ] + application/pgp-encrypted [ Version: 1 ]
+ application/octet-stream; name="msg.asc" + application/octet-stream; name="msg.asc"
{ {
Content-Disposition: inline; filename="msg.asc"; Content-Disposition: inline; filename="msg.asc";
} }
| |
[ opaque encrypted structure ] [ opaque encrypted structure ]
| |
skipping to change at page 15, line 15 skipping to change at page 9, line 15
o the Content-Type header field's o the Content-Type header field's
* "name" parameter is set to the value "msg.asc", and * "name" parameter is set to the value "msg.asc", and
* parameter "forwarded" is set to "no", and * parameter "forwarded" is set to "no", and
o the Content-Disposition header field value is set to "inline" o the Content-Disposition header field value is set to "inline"
* and the "filename" parameter is set to "msg.asc". * and the "filename" parameter is set to "msg.asc".
5.7. S/MIME Compatibility 2.6. S/MIME Compatibility
Interoperability and implementation symmetry between PGP/MIME and Interoperability and implementation symmetry between PGP/MIME and
S/MIME is on the roadmap of pEp. S/MIME is on the roadmap of pEp.
6. Candidate Header Fields for Header Protection 3. Candidate Header Fields for Header Protection
By default, all headers of the original message SHOULD be wrapped By default, all headers of the original message SHOULD be wrapped
with the original message, with one exception: with the original message, with one exception:
o the header field "Bcc" MUST NOT be added to the protected headers. o the header field "Bcc" MUST NOT be added to the protected headers.
7. Stub Outside Headers 4. Stub Outside Headers
The outer message requires a minimal set of headers to be in place The outer message requires a minimal set of headers to be in place
for being eligible for transport. This includes the "From", "To", for being eligible for transport. This includes the "From", "To",
"Cc", "Bcc", "Subject" and "Message-ID" header fields. The protocol "Cc", "Bcc", "Subject" and "Message-ID" header fields. The protocol
hereby defined also depends on the "MIME-Version", "Content-Type", hereby defined also depends on the "MIME-Version", "Content-Type",
"Content-Disposition" and eventually the "Content-Transport-Encoding" "Content-Disposition" and eventually the "Content-Transport-Encoding"
header field to be present. header field to be present.
Submission and forwarding based on SMTP carries "from" and Submission and forwarding based on SMTP carries "from" and
"receivers" information out-of-band, so that the "From" and "To" "receivers" information out-of-band, so that the "From" and "To"
skipping to change at page 16, line 26 skipping to change at page 10, line 26
The following header fields MUST be initialized with proper values The following header fields MUST be initialized with proper values
according to the MIME standards: according to the MIME standards:
o Content-Type o Content-Type
o Content-Disposition o Content-Disposition
o Content-Transport-Encoding (if necessary) o Content-Transport-Encoding (if necessary)
8. Processing Incoming Email under Progressive Header Disclosure 5. Processing Incoming Email under Progressive Header Disclosure
[[ TODO ]] [[ TODO ]]
8.1. Resolving Conflicting Protected and Unprotected Header Fields 5.1. Processing of Signed-only Email
Header field values from the transport message MUST NOT be shown,
when displaying the inner message, or the outer message. The inner
message MUST carry all relevant header fields necessary for display.
8.2. Processing of Signed-only Email
pEp either engages in a signed-and-encrypted communication or in an pEp either engages in a signed-and-encrypted communication or in an
unsigned plaintext communication. Inbound signatures attached to unsigned plaintext communication. Inbound signatures attached to
plaintext messages are duly verified but cannot enhance the perceived plaintext messages are duly verified but cannot enhance the perceived
quality of the message in the user interface (while an invalid quality of the message in the user interface (while an invalid
signature degrades the perception) [I-D.birk-pep]. signature degrades the perception) [I-D.birk-pep].
8.3. Incoming Filter Processing 5.2. Incoming Filter Processing
The Mail User Agent may implement outgoing filtering of mails, which The Mail User Agent may implement outgoing filtering of mails, which
may veto, alter, redirect or replicate the messages. The may veto, alter, redirect or replicate the messages. The
functionality may be implemented on the mailbox server and be functionality may be implemented on the mailbox server and be
configurable through a well-known protocol, e.g., by means of The configurable through a well-known protocol, e.g., by means of The
Sieve Mail-Filtering Language [RFC5490], or be implemented client- Sieve Mail-Filtering Language [RFC5490], or be implemented client-
side, or in a combination of both. side, or in a combination of both.
A mailbox server, which is required to process the full range of A mailbox server, which is required to process the full range of
possible filters, is requiring plaintext access to the header fields. possible filters, is requiring plaintext access to the header fields.
In an end-to-end-encryption context, which pEp enforces by default, In an End-to-End-encryption context, which pEp enforces by default,
upon first reception of the message the mailbox server is limited to upon first reception of the message the mailbox server is limited to
see the transport- relevant headers of the outer wrapper message. A see the transport- relevant headers of the outer wrapper message. A
pEp client configured to trust the server ("trusted server" setting pEp client configured to trust the server ("trusted server" setting
[I-D.marques-pep-email]) will later download the encrypted message, [I-D.marques-pep-email]) will later download the encrypted message,
decrypt it and replace the copy on the server by the decrypted copy. decrypt it and replace the copy on the server by the decrypted copy.
8.3.1. Staged Filtering of Inbound Messages 5.2.1. Staged Filtering of Inbound Messages
Inbound messages are expected to be delivered to the inbox while Inbound messages are expected to be delivered to the inbox while
still being encrypted. At this point in time, server-side filtering still being encrypted. At this point in time, server-side filtering
can only evaluate the unprotected header fields in the wrapper can only evaluate the unprotected header fields in the wrapper
message. message.
In an end-to-end-encryption context, which pEp enforces by default, In an End-to-End-encryption context, which pEp enforces by default,
the mailbox server is limited to see the transport-relevant headers the mailbox server is limited to see the transport-relevant headers
of the outer wrapper message only upon first delivery. A pEp client of the outer wrapper message only upon first delivery. A pEp client
configured to trust the server ("trusted server" setting configured to trust the server ("trusted server" setting
[I-D.marques-pep-email]) will eventually download the encrypted [I-D.marques-pep-email]) will eventually download the encrypted
message, decrypt it locally and replace the copy on the server by the message, decrypt it locally and replace the copy on the server by the
decrypted copy. Server-side message filters SHOULD be able to detect decrypted copy. Server-side message filters SHOULD be able to detect
such post-processed messages, and apply the pending filters. The such post-processed messages, and apply the pending filters. The
client SHOULD easily reflect the post-filtered messages in the user client SHOULD easily reflect the post-filtered messages in the user
interface. interface.
8.4. Outgoing Filter Processing 5.3. Outgoing Filter Processing
The Mail User Agent may implement outgoing filtering of emails, which The Mail User Agent may implement outgoing filtering of emails, which
may veto, alter or replicate the email. They may also hint the MUA may veto, alter or replicate the email. They may also hint the MUA
to store a copy in an alternate "Sent" folder. to store a copy in an alternate "Sent" folder.
Filters which veto the sending or do alter the mail or replicate it Filters which veto the sending or do alter the mail or replicate it
(e.g., mass-mail generators) SHOULD be completed prior to applying (e.g., mass-mail generators) SHOULD be completed prior to applying
protection, and thus also prior to applying header protection. protection, and thus also prior to applying header protection.
Redirection to alternate "Sent" folders MUST NOT be decided prior to Redirection to alternate "Sent" folders MUST NOT be decided prior to
applying protection, but MUAs MAY abide from this restriction if they applying protection, but MUAs MAY abide from this restriction if they
skipping to change at page 18, line 8 skipping to change at page 12, line 5
the specific mailbox server; in this case, MUAs MUST NOT allow to the specific mailbox server; in this case, MUAs MUST NOT allow to
redirect a message to an untrusted server by these rules, to prevent redirect a message to an untrusted server by these rules, to prevent
information leakage to the untrusted server. information leakage to the untrusted server.
[[ TODO: Mention implicit filter for minimal color-rating for message [[ TODO: Mention implicit filter for minimal color-rating for message
replication. ]] replication. ]]
[[ TODO: How to produce key-export-mails manually this way? That is, [[ TODO: How to produce key-export-mails manually this way? That is,
what about non-pEp-mode? ]] what about non-pEp-mode? ]]
9. Security Considerations 6. Security Considerations
[[ TODO ]] [[ TODO ]]
10. Implementation Status 7. Privacy Considerations
10.1. Introduction [[ TODO ]]
8. IANA Considerations
This document has no actions for IANA.
9. Implementation Status
9.1. Introduction
This section records the status of known implementations of the This section records the status of known implementations of the
protocol defined by this specification at the time of posting of this protocol defined by this specification at the time of posting of this
Internet-Draft, and is based on a proposal described in [RFC7942]. Internet-Draft, and is based on a proposal described in [RFC7942].
The description of implementations in this section is intended to The description of implementations in this section is intended to
assist the IETF in its decision processes in progressing drafts to assist the IETF in its decision processes in progressing drafts to
RFCs. Please note that the listing of any individual implementation RFCs. Please note that the listing of any individual implementation
here does not imply endorsement by the IETF. Furthermore, no effort here does not imply endorsement by the IETF. Furthermore, no effort
has been spent to verify the information presented here that was has been spent to verify the information presented here that was
supplied by IETF contributors. This is not intended as, and must not supplied by IETF contributors. This is not intended as, and must not
skipping to change at page 18, line 36 skipping to change at page 12, line 41
features. Readers are advised to note that other implementations may features. Readers are advised to note that other implementations may
exist. exist.
According to [RFC7942], "[...] this will allow reviewers and working According to [RFC7942], "[...] this will allow reviewers and working
groups to assign due consideration to documents that have the benefit groups to assign due consideration to documents that have the benefit
of running code, which may serve as evidence of valuable of running code, which may serve as evidence of valuable
experimentation and feedback that have made the implemented protocols experimentation and feedback that have made the implemented protocols
more mature. It is up to the individual working groups to use this more mature. It is up to the individual working groups to use this
information as they see fit." information as they see fit."
10.2. Current software implementing pEp 9.2. Current software implementing pEp
The following software implementing the pEp protocols (to varying The following software implementing the pEp protocols (to varying
degrees) already exists: degrees) already exists:
o pEp for Outlook as add-on for Microsoft Outlook, release o pEp for Outlook as add-on for Microsoft Outlook, release
[SRC.pepforoutlook] [SRC.pepforoutlook]
o pEp for Android (based on a fork of the K9 MUA), release o pEp for Android (based on a fork of the K9 MUA), release
[SRC.pepforandroid] [SRC.pepforandroid]
skipping to change at page 19, line 4 skipping to change at page 13, line 9
o pEp for Outlook as add-on for Microsoft Outlook, release o pEp for Outlook as add-on for Microsoft Outlook, release
[SRC.pepforoutlook] [SRC.pepforoutlook]
o pEp for Android (based on a fork of the K9 MUA), release o pEp for Android (based on a fork of the K9 MUA), release
[SRC.pepforandroid] [SRC.pepforandroid]
o Enigmail/pEp as add-on for Mozilla Thunderbird, release o Enigmail/pEp as add-on for Mozilla Thunderbird, release
[SRC.enigmailpep] [SRC.enigmailpep]
o pEp for iOS (implemented in a new MUA), beta [SRC.pepforios] o pEp for iOS (implemented in a new MUA), beta [SRC.pepforios]
pEp for Android, iOS and Outlook are provided by pEp Security, a pEp for Android, iOS and Outlook are provided by pEp Security, a
commercial entity specializing in end-user software implementing pEp commercial entity specializing in end-user software implementing pEp
while Enigmail/pEp is pursued as community project, supported by the while Enigmail/pEp is pursued as community project, supported by the
pEp Foundation. pEp Foundation.
All software is available as Free Software and published also in All software is available as Free Software and published also in
source form. source form.
11. Privacy Considerations 10. Acknowledgements
[[ TODO ]]
12. IANA Considerations
This document has no actions for IANA.
13. Acknowledgements
Special thanks go to Krista Bennett and Volker Birk for valuable The authors would like to thank the following people who have
input to this draft and Hernani Marques for reviewing. provided significant contributions or feedback for the development of
this document: Krista Bennett, Volker Birk, Bernie Hoeneisen and
Hernani Marques.
14. References 11. References
14.1. Normative References 11.1. Normative References
[I-D.birk-pep] [I-D.birk-pep]
Marques, H. and B. Hoeneisen, "pretty Easy privacy (pEp): Marques, H. and B. Hoeneisen, "pretty Easy privacy (pEp):
Privacy by Default", draft-birk-pep-03 (work in progress), Privacy by Default", draft-birk-pep-03 (work in progress),
March 2019. March 2019.
[I-D.ietf-lamps-rfc5751-bis]
Schaad, J., Ramsdell, B., and S. Turner, "Secure/
Multipurpose Internet Mail Extensions (S/MIME) Version 4.0
Message Specification", draft-ietf-lamps-rfc5751-bis-12
(work in progress), September 2018.
[I-D.marques-pep-email] [I-D.marques-pep-email]
Marques, H., "pretty Easy privacy (pEp): Email Formats and Marques, H., "pretty Easy privacy (pEp): Email Formats and
Protocols", draft-marques-pep-email-02 (work in progress), Protocols", draft-marques-pep-email-02 (work in progress),
October 2018. October 2018.
[I-D.melnikov-lamps-header-protection] [I-D.melnikov-lamps-header-protection]
Melnikov, A., "Considerations for protecting Email header Melnikov, A., "Considerations for protecting Email header
with S/MIME", draft-melnikov-lamps-header-protection-00 with S/MIME", draft-melnikov-lamps-header-protection-00
(work in progress), October 2018. (work in progress), October 2018.
[PGPMIME] Elkins, M., Del Torto, D., Levien, R., and T. Roessler,
"MIME Security with OpenPGP", RFC 3156,
DOI 10.17487/RFC3156, August 2001,
<https://www.rfc-editor.org/info/rfc3156>.
[RFC2046] Freed, N. and N. Borenstein, "Multipurpose Internet Mail [RFC2046] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part Two: Media Types", RFC 2046, Extensions (MIME) Part Two: Media Types", RFC 2046,
DOI 10.17487/RFC2046, November 1996, DOI 10.17487/RFC2046, November 1996,
<https://www.rfc-editor.org/info/rfc2046>. <https://www.rfc-editor.org/info/rfc2046>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
[RFC3156] Elkins, M., Del Torto, D., Levien, R., and T. Roessler,
"MIME Security with OpenPGP", RFC 3156,
DOI 10.17487/RFC3156, August 2001,
<https://www.rfc-editor.org/info/rfc3156>.
[RFC4880] Callas, J., Donnerhacke, L., Finney, H., Shaw, D., and R. [RFC4880] Callas, J., Donnerhacke, L., Finney, H., Shaw, D., and R.
Thayer, "OpenPGP Message Format", RFC 4880, Thayer, "OpenPGP Message Format", RFC 4880,
DOI 10.17487/RFC4880, November 2007, DOI 10.17487/RFC4880, November 2007,
<https://www.rfc-editor.org/info/rfc4880>. <https://www.rfc-editor.org/info/rfc4880>.
[RFC4949] Shirey, R., "Internet Security Glossary, Version 2", [RFC4949] Shirey, R., "Internet Security Glossary, Version 2",
FYI 36, RFC 4949, DOI 10.17487/RFC4949, August 2007, FYI 36, RFC 4949, DOI 10.17487/RFC4949, August 2007,
<https://www.rfc-editor.org/info/rfc4949>. <https://www.rfc-editor.org/info/rfc4949>.
[RFC5322] Resnick, P., Ed., "Internet Message Format", RFC 5322, [RFC5322] Resnick, P., Ed., "Internet Message Format", RFC 5322,
DOI 10.17487/RFC5322, October 2008, DOI 10.17487/RFC5322, October 2008,
<https://www.rfc-editor.org/info/rfc5322>. <https://www.rfc-editor.org/info/rfc5322>.
[RFC5490] Melnikov, A., "The Sieve Mail-Filtering Language -- [RFC5490] Melnikov, A., "The Sieve Mail-Filtering Language --
Extensions for Checking Mailbox Status and Accessing Extensions for Checking Mailbox Status and Accessing
Mailbox Metadata", RFC 5490, DOI 10.17487/RFC5490, March Mailbox Metadata", RFC 5490, DOI 10.17487/RFC5490, March
2009, <https://www.rfc-editor.org/info/rfc5490>. 2009, <https://www.rfc-editor.org/info/rfc5490>.
[RFC5751] Ramsdell, B. and S. Turner, "Secure/Multipurpose Internet
Mail Extensions (S/MIME) Version 3.2 Message
Specification", RFC 5751, DOI 10.17487/RFC5751, January
2010, <https://www.rfc-editor.org/info/rfc5751>.
[RFC6376] Crocker, D., Ed., Hansen, T., Ed., and M. Kucherawy, Ed., [RFC6376] Crocker, D., Ed., Hansen, T., Ed., and M. Kucherawy, Ed.,
"DomainKeys Identified Mail (DKIM) Signatures", STD 76, "DomainKeys Identified Mail (DKIM) Signatures", STD 76,
RFC 6376, DOI 10.17487/RFC6376, September 2011, RFC 6376, DOI 10.17487/RFC6376, September 2011,
<https://www.rfc-editor.org/info/rfc6376>. <https://www.rfc-editor.org/info/rfc6376>.
[RFC7208] Kitterman, S., "Sender Policy Framework (SPF) for [RFC7208] Kitterman, S., "Sender Policy Framework (SPF) for
Authorizing Use of Domains in Email, Version 1", RFC 7208, Authorizing Use of Domains in Email, Version 1", RFC 7208,
DOI 10.17487/RFC7208, April 2014, DOI 10.17487/RFC7208, April 2014,
<https://www.rfc-editor.org/info/rfc7208>. <https://www.rfc-editor.org/info/rfc7208>.
[RFC7489] Kucherawy, M., Ed. and E. Zwicky, Ed., "Domain-based [RFC7489] Kucherawy, M., Ed. and E. Zwicky, Ed., "Domain-based
Message Authentication, Reporting, and Conformance Message Authentication, Reporting, and Conformance
(DMARC)", RFC 7489, DOI 10.17487/RFC7489, March 2015, (DMARC)", RFC 7489, DOI 10.17487/RFC7489, March 2015,
<https://www.rfc-editor.org/info/rfc7489>. <https://www.rfc-editor.org/info/rfc7489>.
14.2. Informative References [RFC8551] Schaad, J., Ramsdell, B., and S. Turner, "Secure/
Multipurpose Internet Mail Extensions (S/MIME) Version 4.0
Message Specification", RFC 8551, DOI 10.17487/RFC8551,
April 2019, <https://www.rfc-editor.org/info/rfc8551>.
11.2. Informative References
[RFC7942] Sheffer, Y. and A. Farrel, "Improving Awareness of Running [RFC7942] Sheffer, Y. and A. Farrel, "Improving Awareness of Running
Code: The Implementation Status Section", BCP 205, Code: The Implementation Status Section", BCP 205,
RFC 7942, DOI 10.17487/RFC7942, July 2016, RFC 7942, DOI 10.17487/RFC7942, July 2016,
<https://www.rfc-editor.org/info/rfc7942>. <https://www.rfc-editor.org/info/rfc7942>.
[SRC.enigmailpep] [SRC.enigmailpep]
"Source code for Enigmail/pEp", March 2019, "Source code for Enigmail/pEp", July 2019,
<https://enigmail.net/index.php/en/download/source-code>. <https://enigmail.net/index.php/en/download/source-code>.
[SRC.pepforandroid] [SRC.pepforandroid]
"Source code for pEp for Android", March 2019, "Source code for pEp for Android", July 2019,
<https://pep-security.lu/gitlab/android/pep>. <https://pep-security.lu/gitlab/android/pep>.
[SRC.pepforios] [SRC.pepforios]
"Source code for pEp for iOS", March 2019, "Source code for pEp for iOS", July 2019,
<https://pep-security.ch/dev/repos/pEp_for_iOS/>. <https://pep-security.ch/dev/repos/pEp_for_iOS/>.
[SRC.pepforoutlook] [SRC.pepforoutlook]
"Source code for pEp for Outlook", March 2019, "Source code for pEp for Outlook", July 2019,
<https://pep-security.lu/dev/repos/pEp_for_Outlook/>. <https://pep-security.lu/dev/repos/pEp_for_Outlook/>.
Appendix A. Document Changelog Appendix A. About pEp Design Principles
pretty Easy privacy (pEp) is working on bringing state-of-the-art
automatic cryptography known from areas like TLS to electronic mail
(email) communication. pEp is determined to evolve the existing
standards as fundamentally and comprehensively as needed to gain easy
implementation and integration, and for easy use for regular Internet
users. pEp for email wants to attain to good security practice while
still retaining backward compatibility for implementations
widespread.
To provide the required stability as a foundation for good security
practice, pEp for email defines a fixed MIME structure for its
innermost message structure, so to remove most attack vectors which
have permitted the numerous EFAIL vulnerabilities. (TBD: ref)
Security comes just next after privacy in pEp, for which reason the
application of signatures without encryption to messages in transit
is not considered purposeful. pEp for email herein referenced, and
further described in [I-D.marques-pep-email], either expects to
transfer messages in cleartext without signature or encryption, or
transfer them encrypted and with enclosed signature and necessary
public keys so that replies can be immediately upgraded to encrypted
messages.
The pEp message format is equivalent to the S/MIME standard in
ensuring header protection, in that the whole message is protected
instead, by wrapping it and providing cryptographic services to the
whole original message. The pEp message format is different compared
to the S/MIME standard in that the pEp protocols propose
opportunistic End-to-End security and signature, by allowing the
transport of the necessary public key material along with the
original messages.
For the purpose of allowing the insertion of such public keys, the
root entity of the protected message is thus nested once more into an
additional multipart/mixed MIME entity. The current pEp proposal is
for PGP/MIME, while an extension to S/MIME is next.
pEp's proposal is strict in that it requires that the cryptographic
services applied to the protected message MUST include encryption.
It also mandates a fixed MIME structure for the protected message,
which always MUST include a plaintext and optionally an HTML
representation (if HTML is used) of the same message, and requires
that all other optional elements to be eventually presented as
attachments. Alternatively the whole protected message could
represent in turn a wrapped pEp wrapper, which makes the message
structure fully recursive on purpose (e.g., for the purpose of
anonymization through onion routing).
For the purpose of implementing mixnet routing for email, it is
foreseen to nest pEp messages recursively. A protected message can
in turn contain a protected message due for forwarding. This is for
the purpose to increase privacy and counter the necessary leakage of
plaintext addressing in the envelope of the email.
The recursive nature of the pEp message format allows for the
implementation of progressive disclosure of the necessary transport
relevant header fields just as-needed to the next mail transport
agents along the transmission path.
Appendix B. Document Changelog
[[ RFC Editor: This section is to be removed before publication ]] [[ RFC Editor: This section is to be removed before publication ]]
o draft-luck-lamps-pep-header-protection-02 o draft-luck-lamps-pep-header-protection-03
* Remove Use Cases / Requirements sections (move to new doc)
* Adjust title of the document
* Added note on implementation done of forwarded=no
o draft-luck-lamps-pep-header-protection-02
* Add Privacy and IANA Considerations sections * Add Privacy and IANA Considerations sections
* Added / Adjusted requirements * Added / Adjusted requirements
o draft-luck-lamps-pep-header-protection-01 o draft-luck-lamps-pep-header-protection-01
* Major rewrite and update of whole document * Major rewrite and update of whole document
o draft-luck-lamps-pep-header-protection-00 o draft-luck-lamps-pep-header-protection-00
* Initial version * Initial version
Appendix B. Open Issues Appendix C. Open Issues
[[ RFC Editor: This section should be empty and is to be removed [[ RFC Editor: This section should be empty and is to be removed
before publication. ]] before publication. ]]
o Align with specification for MIME Content-Type message/partial o Align with specification for MIME Content-Type message/partial
* We probably have issues and overlapping specifications about * We probably have issues and overlapping specifications about
encoding for nested message/rfc822 entities, specified in encoding for nested message/rfc822 entities, specified in
[RFC2046]. Further study is needed to find and understand the [RFC2046]. Further study is needed to find and understand the
issues. issues.
o Signed-only protection needs further study Author's Address
* pEp only does header protection by applying both signing and
encryption. Technically it is also possible to sign, but not
encrypt the protected messages. This needs further study.
Authors' Addresses
Claudio Luck Claudio Luck
pEp Foundation pEp Foundation
Oberer Graben 4 Oberer Graben 4
CH-8400 Winterthur CH-8400 Winterthur
Switzerland Switzerland
Email: claudio.luck@pep.foundation Email: claudio.luck@pep.foundation
URI: https://pep.foundation/ URI: https://pep.foundation/
Bernie Hoeneisen
Ucom Standards Track Solutions GmbH
CH-8046 Zuerich
Switzerland
Phone: +41 44 500 52 44
Email: bernie@ietf.hoeneisen.ch (bernhard.hoeneisen AT ucom.ch)
URI: https://ucom.ch/
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