Internet DRAFT - draft-lassey-tigress-threat-model
draft-lassey-tigress-threat-model
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.
Internet-Drafts are working documents of the Internet Engineering
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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.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
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Please review these documents carefully, as they describe your rights
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provided without warranty as described in the Revised BSD License.
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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