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Network Working Group H. Marques
Internet-Draft pEp Foundation
Intended status: Informational B. Hoeneisen
Expires: January 8, 2020 Ucom.ch
July 07, 2019
pretty Easy privacy (pEp): Mapping of Privacy Rating
draft-marques-pep-rating-02
Abstract
In many Opportunistic Security scenarios end-to-end encryption is
automatized for Internet users. In addition, it is often required to
provide the users with easy means to carry out authentication.
Depending on several factors, each communication channel to different
peers may have a different Privacy Status, e.g., unencrypted,
encrypted and encrypted as well as authenticated. Even each message
from/to a single peer may have a different Privacy Status.
To display the actual Privacy Status to the user, this document
defines a Privacy Rating scheme and its mapping to a traffic-light
semantics. A Privacy Status is defined on a per-message basis as
well as on a per-identity basis. The traffic-light semantics (as
color rating) allows for a clear and easily understandable
presentation to the user in order to optimize the User Experience
(UX).
This rating system is most beneficial to Opportunistic Security
scenarios and is already implemented in several applications of
pretty Easy privacy (pEp).
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
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
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This Internet-Draft will expire on January 8, 2020.
Copyright Notice
Copyright (c) 2019 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
to this document. Code Components extracted from this document must
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.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 4
1.2. Terms . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Per-Message Privacy Rating . . . . . . . . . . . . . . . . . 5
2.1. Rating Codes . . . . . . . . . . . . . . . . . . . . . . 5
2.2. Color Codes . . . . . . . . . . . . . . . . . . . . . . . 5
2.3. Surjective Mapping of Rating Codes into Color Codes . . . 6
2.4. Semantics of Color and Rating Codes . . . . . . . . . . . 6
2.4.1. Red . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.4.2. No Color . . . . . . . . . . . . . . . . . . . . . . 7
2.4.3. Yellow . . . . . . . . . . . . . . . . . . . . . . . 7
2.4.4. Green . . . . . . . . . . . . . . . . . . . . . . . . 7
3. Per-Identity Privacy Rating . . . . . . . . . . . . . . . . . 8
4. Security Considerations . . . . . . . . . . . . . . . . . . . 8
5. Privacy Considerations . . . . . . . . . . . . . . . . . . . 8
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
7. Implementation Status . . . . . . . . . . . . . . . . . . . . 8
7.1. Introduction . . . . . . . . . . . . . . . . . . . . . . 9
7.2. Current software implementing pEp . . . . . . . . . . . . 9
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 10
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 10
9.1. Normative References . . . . . . . . . . . . . . . . . . 10
9.2. Informative References . . . . . . . . . . . . . . . . . 10
Appendix A. Excerpts from the pEp Reference Implementation . . . 11
A.1. pEp rating . . . . . . . . . . . . . . . . . . . . . . . 11
Appendix B. Document Changelog . . . . . . . . . . . . . . . . . 12
Appendix C. Open Issues . . . . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13
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1. Introduction
In many Opportunistic Security [RFC7435] scenarios end-to-end
encryption is automatized for Internet users. In addition, it is
often required to provide the users with easy means to carry out
authentication.
Depending on several factors, each communication channel to different
identities may have a different Privacy Status, e.g.
o unreliable
o encrypted
o encrypted and authenticated
o mistrusted
Even each message from or to a single peer may have a different
Privacy Status.
To display the actual Privacy Status to the user, this document
defines a Privacy Rating scheme and its mapping to a traffic-light
semantics, i.e., a mapping to different color codes as used in a
traffic-light:
o red
o yellow
o green
o no color (or gray)
Note: While "yellow" color is used in the context of traffic-lights
(e.g., in North America), in other parts of the world (e.g., the UK)
this is generally referred to as "orange" or "amber" lights. For the
scope of this document, "yellow", "amber", and "orange" refer to the
same semantics.
A Privacy Status is defined on a per-message basis as well as on a
per-identity basis. The traffic-light semantics (as color rating)
allows for a clear and easily understandable presentation to the user
in order to optimize the User Experience (UX). To serve also
(color-)blind Internet users or those using monochrome displays, the
traffic light color semantics may also be presented by simple texts
and symbols for signaling the corresponding Privacy Status.
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The proposed definitions are already implemented and used in
applications of pretty Easy privacy (pEp) [I-D.birk-pep]. This
document is targeted to applications based on the pEp framework and
Opportunistic Security [RFC7435]. However, it may be also used in
other applications as suitable.
Note: The pEp [I-D.birk-pep] framework proposes to automatize the use
of end-to-end encryption for Internet users of email and other
messaging applications and introduces methods to easily allow
authentication.
1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
1.2. Terms
The following terms are defined for the scope of this document:
o pEp Handshake: The process of one user contacting another over an
independent channel in order to verify Trustwords (or by fallback:
fingerprints). This can be done in-person or through established
verbal communication channels, like a phone call.
[I-D.marques-pep-handshake]
o Trustwords: A scalar-to-word representation of 16-bit numbers (0
to 65535) to natural language words. When doing a Handshake,
peers are shown combined Trustwords of both public keys involved
to ease the comparison. [I-D.birk-pep-trustwords]
o Trust On First Use (TOFU): cf. [RFC7435], which states: "In a
protocol, TOFU calls for accepting and storing a public key or
credential associated with an asserted identity, without
authenticating that assertion. Subsequent communication that is
authenticated using the cached key or credential is secure against
an MiTM attack, if such an attack did not succeed during the
vulnerable initial communication."
o Man-in-the-middle (MITM) attack: cf. [RFC4949], which states: "A
form of active wiretapping attack in which the attacker intercepts
and selectively modifies communicated data to masquerade as one or
more of the entities involved in a communication association."
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2. Per-Message Privacy Rating
2.1. Rating Codes
To rate messages (cf. also Appendix A.1), the following 13 Rating
codes are defined as scalar values (decimal):
+-------------+------------------------+
| Rating code | Rating label |
+-------------+------------------------+
| -3 | under attack |
| | |
| -2 | broken |
| | |
| -1 | mistrust |
| | |
| 0 | undefined |
| | |
| 1 | cannot decrypt |
| | |
| 2 | have no key |
| | |
| 3 | unencrypted |
| | |
| 4 | unencrypted for some |
| | |
| 5 | unreliable |
| | |
| 6 | reliable |
| | |
| 7 | trusted |
| | |
| 8 | trusted and anonymized |
| | |
| 9 | fully anonymous |
+-------------+------------------------+
2.2. Color Codes
For an Internet user to understand what the available Privacy Status
is, the following colors (traffic-light semantics) are defined:
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+------------+-------------+
| Color code | Color label |
+------------+-------------+
| -1 | red |
| | |
| 0 | no color |
| | |
| 1 | yellow |
| | |
| 2 | green |
+------------+-------------+
2.3. Surjective Mapping of Rating Codes into Color Codes
Corresponding User Experience (UX) implementations use a surjective
mapping of the Rating Codes into the Color Codes (in traffic light
semantics) as follows:
+--------------+------------+-------------+
| Rating codes | Color code | Color label |
+--------------+------------+-------------+
| -3 to -1 | -1 | red |
| | | |
| 0 to 5 | 0 | no color |
| | | |
| 6 | 1 | yellow |
| | | |
| 7 to 9 | 2 | green |
+--------------+------------+-------------+
This mapping is used in current pEp implementations to signal the
Privacy Status (cf. Section 7.2).
2.4. Semantics of Color and Rating Codes
2.4.1. Red
The red color MUST only be used in three cases:
o Rating code -3: A man-in-the-middle (MITM) attack could be
detected.
o Rating code -2: The message was tempered with.
o Rating code -1: The user explicitly states he mistrusts a peer,
e.g., because a Handshake [I-D.marques-pep-handshake] mismatched
or when the user learns the communication partner was attacked and
might have gotten the corresponding secret key leaked.
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2.4.2. No Color
No specific (or a gray color) MUST be shown in the following cases:
o Rating code 0: A message can be rendered, but the encryption
status is not clear, i.e., undefined
o Rating code 1: A message cannot be decrypted (because of an error
not covered by rating code 2 below).
o Rating code 2: No key is available to decrypt a message (because
it was encrypted with a public key for which no secret key could
be found).
o Rating code 3: A message is received or sent out unencrypted
(because it was received unencrypted or there's no public key to
encrypt a message to a recipient).
o Rating code 4: A message is sent out unencrypted for some of the
recipients of a group (because there's at least one recipient in
the group whose public key is not available to the sender).
o Rating code 5: A message is encrypted, but cryptographic
parameters (e.g., the cryptographic method employed or key length)
are insufficient.
2.4.3. Yellow
o Rating code 6: Whenever a message can be encrypted or decrypted
with sufficient cryptographic parameters, it's considered
reliable. It is mapped into the yellow color code.
2.4.4. Green
o Rating code 7: A message is mapped into the green color code only
if a pEp handshake [I-D.marques-pep-handshake] was successfully
carried out.
By consequence that means, that the pEp propositions don't strictly
follow the TOFU (cf. [RFC7435]) approach, in order to avoid
signaling trust without peers verifying their channel first.
In current pEp implementations (cf. Section 7) only rating code 7 is
achieved.
The rating codes 8 and 9 are reserved for future use in pEp
implementations which also secure meta-data (rating code 8), by using
a peer-to-peer framework like GNUnet [GNUnet], and/or allow for fully
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anonymous communications (rating code 9), where sender and receiver
don't know each other, but trust between the endpoints could be
established nevertheless.
3. Per-Identity Privacy Rating
The same Color Codes (red, no color, yellow and green) as for
messages (cf. Section 2.2) MUST be applied for identities (peers),
so that a user can easily understand, which identities private
communication is possible with.
The green color code MUST be applied to an identity whom the pEp
handshake [I-D.marques-pep-handshake] was successfully carried out
with.
The yellow color code MUST be set whenever a public key could be
obtained to securely encrypt messages to an identity, although a MITM
attack cannot be excluded.
The no color code MUST be used for the case that no public key is
available to engage in private communications with an identity.
The red color code MUST only be used when an identity is marked as
mistrusted.
[[ It's not yet clear if there are proper cases where it makes sense
to set an identity automatically to the red color code, as it appears
to be difficult to detect attacks (e.g., secret key leakage) at the
other endpoint with certainty. ]]
4. Security Considerations
[[ TODO ]]
5. Privacy Considerations
[[ TODO ]]
6. IANA Considerations
This document has no actions for IANA.
7. Implementation Status
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7.1. Introduction
This section records the status of known implementations of the
protocol defined by this specification at the time of posting of this
Internet-Draft, and is based on a proposal described in [RFC7942].
The description of implementations in this section is intended to
assist the IETF in its decision processes in progressing drafts to
RFCs. Please note that the listing of any individual implementation
here does not imply endorsement by the IETF. Furthermore, no effort
has been spent to verify the information presented here that was
supplied by IETF contributors. This is not intended as, and must not
be construed to be, a catalog of available implementations or their
features. Readers are advised to note that other implementations may
exist.
According to [RFC7942], "[...] this will allow reviewers and working
groups to assign due consideration to documents that have the benefit
of running code, which may serve as evidence of valuable
experimentation and feedback that have made the implemented protocols
more mature. It is up to the individual working groups to use this
information as they see fit."
7.2. Current software implementing pEp
The following software implementing the pEp protocols (to varying
degrees) already exists:
o pEp for Outlook as add-on for Microsoft Outlook, release
[SRC.pepforoutlook]
o pEp for Android (based on a fork of the K9 MUA), release
[SRC.pepforandroid]
o Enigmail/pEp as add-on for Mozilla Thunderbird, release
[SRC.enigmailpep]
o pEp for iOS (implemented in a new MUA), beta [SRC.pepforios]
pEp for Android, iOS and Outlook are provided by pEp Security, a
commercial entity specializing in end-user software implementing pEp
while Enigmail/pEp is pursued as community project, supported by the
pEp Foundation.
All software is available as Free Software and published also in
source form.
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8. Acknowledgements
The authors would like to thank the following people who have
provided feedback or significant contributions to the development of
this document: Leon Schumacher and Volker Birk
This work was initially created by pEp Foundation, and then reviewed
and extended with funding by the Internet Society's Beyond the Net
Programme on standardizing pEp. [ISOC.bnet]
9. References
9.1. Normative References
[I-D.birk-pep]
Marques, H. and B. Hoeneisen, "pretty Easy privacy (pEp):
Privacy by Default", draft-birk-pep-03 (work in progress),
March 2019.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC4949] Shirey, R., "Internet Security Glossary, Version 2",
FYI 36, RFC 4949, DOI 10.17487/RFC4949, August 2007,
<https://www.rfc-editor.org/info/rfc4949>.
[RFC7435] Dukhovni, V., "Opportunistic Security: Some Protection
Most of the Time", RFC 7435, DOI 10.17487/RFC7435,
December 2014, <https://www.rfc-editor.org/info/rfc7435>.
9.2. Informative References
[GNUnet] Grothoff, C., "The GNUnet System", October 2017,
<https://grothoff.org/christian/habil.pdf>.
[I-D.birk-pep-trustwords]
Birk, V., Marques, H., and B. Hoeneisen, "IANA
Registration of Trustword Lists: Guide, Template and IANA
Considerations", draft-birk-pep-trustwords-03 (work in
progress), March 2019.
[I-D.marques-pep-handshake]
Marques, H. and B. Hoeneisen, "pretty Easy privacy (pEp):
Contact and Channel Authentication through Handshake",
draft-marques-pep-handshake-02 (work in progress), March
2019.
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[ISOC.bnet]
Simao, I., "Beyond the Net. 12 Innovative Projects
Selected for Beyond the Net Funding. Implementing Privacy
via Mass Encryption: Standardizing pretty Easy privacy's
protocols", June 2017, <https://www.internetsociety.org/
blog/2017/06/12-innovative-projects-selected-for-beyond-
the-net-funding/>.
[RFC7942] Sheffer, Y. and A. Farrel, "Improving Awareness of Running
Code: The Implementation Status Section", BCP 205,
RFC 7942, DOI 10.17487/RFC7942, July 2016,
<https://www.rfc-editor.org/info/rfc7942>.
[SRC.enigmailpep]
"Source code for Enigmail/pEp", July 2019,
<https://enigmail.net/index.php/en/download/source-code>.
[SRC.pepforandroid]
"Source code for pEp for Android", July 2019,
<https://pep-security.lu/gitlab/android/pep>.
[SRC.pepforios]
"Source code for pEp for iOS", July 2019,
<https://pep-security.ch/dev/repos/pEp_for_iOS/>.
[SRC.pepforoutlook]
"Source code for pEp for Outlook", July 2019,
<https://pep-security.lu/dev/repos/pEp_for_Outlook/>.
Appendix A. Excerpts from the pEp Reference Implementation
This section provides excerpts of the running code from the pEp
reference implementation pEp engine (C99 programming language).
A.1. pEp rating
From the reference implementation by the pEp foundation, src/
message_api.h:
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typedef enum _PEP_rating {
PEP_rating_undefined = 0,
PEP_rating_cannot_decrypt,
PEP_rating_have_no_key,
PEP_rating_unencrypted,
PEP_rating_unencrypted_for_some,
PEP_rating_unreliable,
PEP_rating_reliable,
PEP_rating_trusted,
PEP_rating_trusted_and_anonymized,
PEP_rating_fully_anonymous,
PEP_rating_mistrust = -1,
PEP_rating_b0rken = -2,
PEP_rating_under_attack = -3
} PEP_rating;
Appendix B. Document Changelog
[[ RFC Editor: This section is to be removed before publication ]]
o draft-marques-pep-rating-02:
* Add Privacy and IANA Considerations sections
* Updated Terms
o draft-marques-pep-rating-01:
* Update references
* Minor edits
o draft-marques-pep-rating-00:
* Initial version
Appendix C. Open Issues
[[ RFC Editor: This section should be empty and is to be removed
before publication ]]
o Better explain usage of Color Codes in Per-Identity Privacy Rating
o Decide whether rating code scalars 6 and 7-9 should be raised to
leave space for future extensions
o Add Security Considerations
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o Add more source code excerpts to Appendix
o Add rating codes for secure cryptographic methods and parameters
and reference them
Authors' Addresses
Hernani Marques
pEp Foundation
Oberer Graben 4
CH-8400 Winterthur
Switzerland
Email: hernani.marques@pep.foundation
URI: https://pep.foundation/
Bernie Hoeneisen
Ucom Standards Track Solutions GmbH
CH-8046 Zuerich
Switzerland
Phone: +41 44 500 52 40
Email: bernie@ietf.hoeneisen.ch (bernhard.hoeneisen AT ucom.ch)
URI: https://ucom.ch/
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