TIGRESS Threat Model
draft-lassey-tigress-threat-model-00

Transfer dIGital cREdentialS Securely                          B. Lassey
Internet-Draft                                                    Google
Intended status: Informational                           3 February 2023
Expires: 7 August 2023

                          TIGRESS Threat Model
                  draft-lassey-tigress-threat-model-00

Abstract

   TODO Abstract

About This Document

   This note is to be removed before publishing as an RFC.

   The latest revision of this draft can be found at
   https://bslassey.github.io/tigress-threat-model/draft-lassey-tigress-
   threat-model.html.  Status information for this document may be found
   at https://datatracker.ietf.org/doc/draft-lassey-tigress-threat-
   model/.

   Discussion of this document takes place on the Transfer dIGital
   cREdentialS Securely Working Group mailing list
   (mailto:tigress@ietf.org), which is archived at
   https://mailarchive.ietf.org/arch/browse/tigress/.  Subscribe at
   https://www.ietf.org/mailman/listinfo/tigress/.

   Source for this draft and an issue tracker can be found at
   https://github.com/bslassey/tigress-threat-model.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on 7 August 2023.

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Copyright Notice

   Copyright (c) 2023 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Privacy goals:  . . . . . . . . . . . . . . . . . . . . .   2
     1.2.  Security goals: . . . . . . . . . . . . . . . . . . . . .   2
     1.3.  Functional goals: . . . . . . . . . . . . . . . . . . . .   3
   2.  Threat Model  . . . . . . . . . . . . . . . . . . . . . . . .   3
     2.1.  If an intermediary server is used . . . . . . . . . . . .   4
   3.  Conventions and Definitions . . . . . . . . . . . . . . . . .   5
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   5.  Normative References  . . . . . . . . . . . . . . . . . . . .   5
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .   6
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   The TIGRESS Working Group is chartered to deliver a protocol for
   transferring copies of digital credentials.  The charter specifies
   certain goals:

1.1.  Privacy goals:

   *  The relay server should not see sensitive details of the share

   *  The relay server should not be able to provision the credential
      itself, acting as an intermediary for the recipient (person-in-
      the-middle, impersonation attack)

   *  Aside from network-level metadata, the relay server should not
      learn information about the sender or receiver

1.2.  Security goals:

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   *  Ensure only the intended recipient is able to provision the
      credential

   *  Ensure the credential can only be provisioned once (anti-replay)

   *  Ensure the sender has the intent to transfer (proof of the fact
      that the share initiation is attributed to a valid device and a
      user)

1.3.  Functional goals:

   *  Allow a sender to initiate a share and select a relay server

   *  Allow a recipient to view the share request, and provision the
      credential associated with the share upon receipt

   *  Allow a sender and a recipient to perform multiple round trip
      communications within a limited time frame

   *  Not require that both the sender and recipient have connectivity
      to the relay server at the same time

   *  Support opaque message content based on the credential type

   *  Support a variety of types of credentials, to include those
      adhering to public standards (e.g., Car Connectivity Consortium)
      and proprietary (i.e., non-public or closed community) formats

   From these goals we can derive a threat model for the general problem
   space.

2.  Threat Model

   ## Assets and Data ### Credential The credential or key that is being
   shared via this protocol. ### Intermediary data Data that is shared
   over the course of the transaction. ### Share invitation The initial
   data shared with the reciever which represents an invitation to share
   a credential. # Users ## Sender The user who initiates the share. ##
   Receiver The user who is the intended recipient and accepts the
   invitation to share a credential. # Attackers and Motivations #
   Threats and mitigations

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   +==================+============+========+==========================+
   | Threat           | Likelihood | Impact | Mitigations              |
   | Description      |            |        |                          |
   +==================+============+========+==========================+
   | An Attacker with | MED        | HIGH   | Implementors SHOULD      |
   | physical access  |            |        | take sufficient          |
   | to the victim's  |            |        | precautions to ensure    |
   | phone initiates  |            |        | that the device owner    |
   | a share of a     |            |        | is in possession of      |
   | Credential to    |            |        | the device when          |
   | the the          |            |        | initiating a share       |
   | Attacker's       |            |        | such as requiring        |
   | device           |            |        | authentication at        |
   |                  |            |        | share time               |
   +------------------+------------+--------+--------------------------+
   | Attacker         | HIGH       | HIGH   |                          |
   | intercepts or    |            |        |                          |
   | eavesdrops on    |            |        |                          |
   | sharing message  |            |        |                          |
   +------------------+------------+--------+--------------------------+
   | Sender           | HIGH       | HIGH   | Implementors should      |
   | mistakenly sends |            |        | ensure any initiated     |
   | to the wrong     |            |        | shares can be            |
   | Receiver         |            |        | withdrawn or revoked     |
   |                  |            |        | at any time.             |
   +------------------+------------+--------+--------------------------+
   | Sender device    | MED        | HIGH   |                          |
   | compromised      |            |        |                          |
   +------------------+------------+--------+--------------------------+

                                  Table 1

2.1.  If an intermediary server is used

   Some designs may rely on an intermediary server to facilitate the
   transfer of material.  Below are threats and mitigations assuming
   that there is an intermediary server hosting encrypted content at an
   "unguessible" location.

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   +=====================+============+========+======================+
   | Threat Description  | Likelihood | Impact | Mitigations          |
   +=====================+============+========+======================+
   | Attacker brute      | LOW        | LOW    | Limited TTL of       |
   | forces              |            |        | storage, rate        |
   | "unguessible"       |            |        | limiting of requests |
   | location            |            |        |                      |
   +---------------------+------------+--------+----------------------+
   | Attacker intercepts | MED        | MED    | Seperate             |
   | encryption key      |            |        | transimission of     |
   |                     |            |        | encryption key and   |
   |                     |            |        | unguessible location |
   +---------------------+------------+--------+----------------------+
   | Attacker intercepts | MED        | HIGH   | Implementor should   |
   | encryption key and  |            |        | warn users about     |
   | unguessible         |            |        | sharing credentials  |
   | location            |            |        | to groups            |
   +---------------------+------------+--------+----------------------+
   | Attacker            | LOW        | LOW    | Content on the       |
   | compromises         |            |        | server is encrypted  |
   | intermediary server |            |        |                      |
   +---------------------+------------+--------+----------------------+
   | Attacker uses       | HIGH       | LOW    | intermediary server  |
   | intermediary server |            |        | should have tight    |
   | to store unrelated  |            |        | size limits and TTLS |
   | items (i.e. cat     |            |        | to discourage misuse |
   | pictures)           |            |        |                      |
   +---------------------+------------+--------+----------------------+

                                 Table 2

3.  Conventions and Definitions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

4.  IANA Considerations

   This document has no IANA actions.

5.  Normative References

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   [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/rfc/rfc2119>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/rfc/rfc8174>.

Acknowledgments

   This document took as inspiration the threat model
   (https://github.com/dimmyvi/tigress-sample-implementation/blob/main/
   draft-tigress-sample-implementation.md#threat-model) that was part of
   Dmitry Vinokurov's sample implementation document.

Author's Address

   Brad Lassey
   Google
   Email: lassey@google.com

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