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Versions: 00 01

Network Working Group                                         H. Marques
Internet-Draft                                            pEp Foundation
Intended status: Informational                              B. Hoeneisen
Expires: September 12, 2019                                      Ucom.ch
                                                          March 11, 2019


          pretty Easy privacy (pEp): Mapping of Privacy Rating
                      draft-marques-pep-rating-01

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 September 12, 2019.

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
   2.  Terms . . . . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Per-Message Privacy Rating  . . . . . . . . . . . . . . . . .   4
     3.1.  Rating Codes  . . . . . . . . . . . . . . . . . . . . . .   4
     3.2.  Color Codes . . . . . . . . . . . . . . . . . . . . . . .   5
     3.3.  Surjective Mapping of Rating Codes into Color Codes . . .   6
     3.4.  Semantics of Color and Rating Codes . . . . . . . . . . .   6
       3.4.1.  Red . . . . . . . . . . . . . . . . . . . . . . . . .   6
       3.4.2.  No Color  . . . . . . . . . . . . . . . . . . . . . .   6
       3.4.3.  Yellow  . . . . . . . . . . . . . . . . . . . . . . .   7
       3.4.4.  Green . . . . . . . . . . . . . . . . . . . . . . . .   7
   4.  Per-Identity Privacy Rating . . . . . . . . . . . . . . . . .   7
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   6.  Implementation Status . . . . . . . . . . . . . . . . . . . .   8
     6.1.  Introduction  . . . . . . . . . . . . . . . . . . . . . .   8
     6.2.  Current software implementing pEp . . . . . . . . . . . .   9
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   9
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   9
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  10
   Appendix A.  Excerpts from the pEp Reference Implementation . . .  11
     A.1.  pEp rating  . . . . . . . . . . . . . . . . . . . . . . .  11
   Appendix B.  Document Changelog . . . . . . . . . . . . . . . . .  11
   Appendix C.  Open Issues  . . . . . . . . . . . . . . . . . . . .  11
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  12







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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.

2.  Terms

   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].

   o  pEp Handshake: The process when Alice - e.g., in-person or via
      phone - contacts Bob to verify Trustwords (or by fallback:
      fingerprints) is called pEp Handshake.
      [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]

   o  Man-in-the-middle attack (MITM): cf. [RFC4949]

3.  Per-Message Privacy Rating

3.1.  Rating Codes

   To rate messages (cf. also Appendix A.1), the following 13 Rating
   codes are defined as scalar values (decimal):














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                 +-------------+------------------------+
                 | 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 |
                 +-------------+------------------------+

3.2.  Color Codes

   For an Internet user to understand what the available Privacy Status
   is, the following colors (traffic-light semantics) are defined:

                       +------------+-------------+
                       | Color code | Color label |
                       +------------+-------------+
                       | -1         |         red |
                       |            |             |
                       | 0          |    no color |
                       |            |             |
                       | 1          |      yellow |
                       |            |             |
                       | 2          |       green |
                       +------------+-------------+





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3.3.  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 6.2).

3.4.  Semantics of Color and Rating Codes

3.4.1.  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.

3.4.2.  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).





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   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.

3.4.3.  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.

3.4.4.  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 6) 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
   anonymous communications (rating code 9), where sender and receiver
   don't know each other, but trust between the endpoints could be
   established nevertheless.

4.  Per-Identity Privacy Rating

   The same Color Codes (red, no color, yellow and green) as for
   messages (cf.  Section 3.2) MUST be applied for identities (peers),
   so that a user can easily understand, which identities private
   communication is possible with.



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   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.  ]]

5.  Security Considerations

   [[ TODO ]]

6.  Implementation Status

6.1.  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."





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6.2.  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.

7.  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]

8.  References

8.1.  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>.




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   [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>.

8.2.  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-02 (work in
              progress), June 2018.

   [I-D.marques-pep-handshake]
              Marques, H. and B. Hoeneisen, "pretty Easy privacy (pEp):
              Contact and Channel Authentication through Handshake",
              draft-marques-pep-handshake-01 (work in progress), October
              2018.

   [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", March 2019,
              <https://enigmail.net/index.php/en/download/source-code>.

   [SRC.pepforandroid]
              "Source code for pEp for Android", March 2019,
              <https://pep-security.lu/gitlab/android/pep>.






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   [SRC.pepforios]
              "Source code for pEp for iOS", March 2019,
              <https://pep-security.ch/dev/repos/pEp_for_iOS/>.

   [SRC.pepforoutlook]
              "Source code for pEp for Outlook", March 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:

         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-birk-pep-rating-00:

      *  Initial version

Appendix C.  Open Issues

   [[ RFC Editor: This section should be empty and is to be removed
   before publication ]]




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   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

   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 44
   Email: bernie@ietf.hoeneisen.ch (bernhard.hoeneisen AT ucom.ch)
   URI:   https://ucom.ch/



















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