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 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." This Internet-Draft will expire on 7 August 2023. Lassey Expires 7 August 2023 [Page 1] Internet-Draft TIGRESS Threat Model February 2023 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/ 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 Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are 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: Lassey Expires 7 August 2023 [Page 2] Internet-Draft TIGRESS Threat Model February 2023 * 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 Lassey Expires 7 August 2023 [Page 3] Internet-Draft TIGRESS Threat Model February 2023 +==================+============+========+==========================+ | 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. Lassey Expires 7 August 2023 [Page 4] Internet-Draft TIGRESS Threat Model February 2023 +=====================+============+========+======================+ | 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 Lassey Expires 7 August 2023 [Page 5] Internet-Draft TIGRESS Threat Model February 2023 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . 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 Lassey Expires 7 August 2023 [Page 6]