Internet-Draft tigress-requirements November 2022
Vinokurov, et al. Expires 13 May 2023 [Page]
Workgroup:
TIGRESS
Internet-Draft:
draft-tigress-requirements-04
Published:
Intended Status:
Informational
Expires:
Authors:
D. Vinokurov
Apple Inc
C. Astiz
Apple Inc
A. Pelletier
Apple Inc
J. L. Giraud
Apple Inc
A. Bulgakov
Apple Inc
M. Byington
Apple Inc
N. Sha
Alphabet Inc
M. Gerster
Mercedes-Benz AG

Transfer Digital Credentials Securely - Requirements

Abstract

This document describes the use cases necessitating the secure transfer of digital credentials, residing in a digital wallet, between two devices and defines general assumptions, requirements and the scope of the corresponding Tigress Internet-draft [Tigress-00].

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://datatracker.ietf.org/doc/draft-tigress-requirements/. Status information for this document may be found at https://datatracker.ietf.org/doc/draft-tigress-requirements/.

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

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 13 May 2023.

Table of Contents

1. Introduction

Today, there is no widely accepted way of transferring digital credentials securely between two digital wallets independent of hardware and software manufacturer. This document describes the problem space and the requirements for the solution the working group creates.

Tigress allows for a sender and receiver to communicate in order to facilitate a secure credential transfer between two digital wallets. Tigress also specifies certain privacy requirements in order to maintain a high level of user privacy.

2. General Setting

When sharing digital secure credentials, there are several actors involved. While the Tigress working group's solution will focus on sharing information between two digital wallets, potentially through an intermediary server, there are a couple more actors involved.

The companies that are providing the digital credential for consumption by a digital wallet are the provisioning partners. They are in control of the provisioning information and the lifecycle of the credentials. Each digital wallet has a preexisting trust relationship between itself and the Provisioning Partner.

The interface between the devices and the Provisioning Partner can be proprietary or a part of published specifications such as the [CCC-Digital-Key-30]. The sender obtains provisioning information from the provisioning partner, then shares it to the recipient via Tigress. The recipient then takes that data and sends it to the Provisioning Partner to redeem a credential for consumption in a digital wallet.

For some credential types the Provisioning Partner who mints new credentials is actually the sender. In that scenario the receiver will generate a new key material at the request of the sender, and then communicate with the sender over Tigress to have its key material signed by the sender.

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.

General terms:

4. Use Cases

5. Relationships

mermaid sequenceDiagram actor S as Sender participant I as Intermediary actor R as Receiver S ->> I : upload credential data break Generic messaging channel S ->> R : send invite end Loop Provision credential R ->> I : request credential data I ->> R : deliver credential data end

6. Assumptions

7. Requirements

7.1. Intermediary server requirments

If the solution requires an intermediary server, it should have the following requirements.

  • (Req-Privacy) An Intermediary server SHALL not be able to correlate users between exchanges, or create a social graph. Intermediary server shall not be an arbiter of Identity.
  • (Req-Notify) Solution SHOULD support a notification mechanism to inform devices on the content update on Intermediary server.
  • (Req-Opaque) Message content between Sender and Receiver MUST be opaque to an Intermediary.
  • (Req-IntermediaryAttestation) An Intermediary SHALL implement mechanisms to prevent abuse by share initiating device, verifying that the device is in good standing and content generated by the sender device can be trusted by the Intermediary. The trust mechanism could be proprietary or publicly verifiable ( e.g. WebAuthN).
  • (Req-ReceiverTrust) The Receiver device SHOULD be able to evaluate the trustworthiness of the Intermediary using a list of trusted/approved intermediaries.

8. Review of existing solutions

A number of existing solutions / protocols have been reviewed in order to be used for secure credential transfer based on the requirements: GSS-API, Kerberos, AWS S3, email, Signal. None of the existing protocols comply with the requirements; the effort of modifying the existing protocols has been accessed to be significantly higher than introducing a new solution to solve this problem. The goal of the Tigress draft [Tigress-00] is not to define a new encryption or secure message exchange protocol, but rather a standardized mechanism of exchanging access-specific encrypted credential information.

8.1. Arbitrary Messaging Channel (Email / WhatsApp / SMS / Signal / etc.)

The Provisioning Information MAY be sent from Sender to Receiver over an arbitrary messaging channel that supports binary file transfer, but this would not support provisioning flows which require multiple round trips as requied by (Req-RoundTrips). The same requirement applies to Signal protocol outside of the Signal app, as the Req-RoundTrips would likely be difficult and add a lot of friction for the user.

8.2. GSS-API, Kerberos

GSS-API [RFC2078] and Kerberos [RFC4120] are authentication technologies which could be used to authenticate Sender, Receiver and intermediary. However, as they provide strong authentication, they would allow the Intermediary server to build a social graph in violation of (Req-Privacy). Their setup also require strong coordination between the actors of the system which seems overly costly for the intended system. AWS S3 could be used as an Intermediary server but it would force all participants to use a specific cloud service which is in violation of (Req-AnyPlatorm).

9. Out of Scope

10. Security Considerations

TODO Security

11. IANA Considerations

This document has no IANA actions.

12. Normative References

[CCC-Digital-Key-30]
Car Connectivity Consortium, "Digital Key Release 3", , <https://carconnectivity.org/download-digital-key-3-specification/>.
[RFC2078]
Linn, J., "Generic Security Service Application Program Interface, Version 2", RFC 2078, DOI 10.17487/RFC2078, , <https://www.rfc-editor.org/rfc/rfc2078>.
[RFC2119]
Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, , <https://www.rfc-editor.org/rfc/rfc2119>.
[RFC4120]
Neuman, C., Yu, T., Hartman, S., and K. Raeburn, "The Kerberos Network Authentication Service (V5)", RFC 4120, DOI 10.17487/RFC4120, , <https://www.rfc-editor.org/rfc/rfc4120>.
[RFC8174]
Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, , <https://www.rfc-editor.org/rfc/rfc8174>.
[Tigress-00]
Vinokurov, D., Byington, M., Lerch, M., Pelletier, A., and N. Sha, "Transfer Digital Credentials Securely", , <https://datatracker.ietf.org/doc/draft-art-tigress/>.

Acknowledgments

TODO acknowledge.

Authors' Addresses

Dmitry Vinokurov
Apple Inc
Casey Astiz
Apple Inc
Alex Pelletier
Apple Inc
Jean-Luc Giraud
Apple Inc
Alexey Bulgakov
Apple Inc
Matt Byington
Apple Inc
Nick Sha
Alphabet Inc
Manuel Gerster
Mercedes-Benz AG