TIGRESS D. Vinokurov
Internet-Draft C. Astiz
Intended status: Informational A. Pelletier
Expires: 10 May 2023 J. L. Giraud
A. Bulgakov
M. Byington
Apple Inc
N. Sha
Alphabet Inc
M. Gerster
Mercedes-Benz AG
6 November 2022
Transfer Digital Credentials Securely - Requirements
draft-tigress-requirements-03
Abstract
This document describes the use cases necessitating the secure
transfer of digital credentials 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
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions and Definitions . . . . . . . . . . . . . . . . . 3
3. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Relationships . . . . . . . . . . . . . . . . . . . . . . . . 4
5. Assumptions . . . . . . . . . . . . . . . . . . . . . . . . . 4
6. Requirements . . . . . . . . . . . . . . . . . . . . . . . . 5
6.1. Intermediary server requirments . . . . . . . . . . . . . 6
7. Review of existing solutions . . . . . . . . . . . . . . . . 6
7.1. Arbitrary Messaging Channel (Email / WhatsApp / SMS /
Signal / etc.) . . . . . . . . . . . . . . . . . . . . . 7
7.2. GSS-API, Kerberos . . . . . . . . . . . . . . . . . . . . 7
7.3. Signal Protocol . . . . . . . . . . . . . . . . . . . . . 7
8. Out of Scope . . . . . . . . . . . . . . . . . . . . . . . . 7
9. Security Considerations . . . . . . . . . . . . . . . . . . . 8
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
11. Normative References . . . . . . . . . . . . . . . . . . . . 8
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
TODO Introduction
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2. 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:
* Credential information - data used to authenticate the user with
an access point.
* Provisioning information - data transferred from Sender to
Receiver device that is both necessary and sufficient for the
Receiver to request a new credential from Provisioning Partner to
provision it to the Receiver device.
* Provisioning - A process of adding a new credential to the device.
* Provisioning Partner - an entity which facilitates Credential
Information lifecycle on a device. Lifecycle may include
provisioning of credential, credential termination, credential
update.
* Sender (device) - a device initiating a transfer of Provisioning
Information to a Receiver that can provision this credential.
* Receiver (device) - a device that receives Provisioning
Information and uses it to provision a new credential.
* Intermediary (server) - an intermediary server that provides a
standardized and platform-independent way of transferring
provisioning information between Sender and Receiver devices.
3. Use Cases
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* Let's say Ben owns a vehicle that supports digital keys which
comply with the CCC [CCC-Digital-Key-30] open standard. Ben would
like to let Ryan borrow the car for the weekend. Ryan and Ben are
using two different mobile phones with different operating
systems. In order for Ben to share his car key to Ryan for a
weekend, he must transfer some data to the receiver device. The
data structure shared between the two participants is defined in
the CCC. In addition, the CCC requires the receiver to generate
required key material and return it to the sender to sign and
return back to the receiver. At this point, the receiver now has
a token that will allow them to provision their new key with the
car.
* Bob booked a room at a hotel for the weekend, but will be arriving
late at night. Alice, his partner, comes to the hotel first, so
Bob wants to share his key to the room with Alice. Bob and Alice
are using two different mobile phones with different operating
systems. In order for Bob to share his key to the hotel to Alice
for a weekend, he must transfer some data to her device. The data
structure shared between the two participants is proprietary to
the given hotel chain (or Provisioning Partner). This data
transfer is a one-time, unidirectional from Bob's device to
Alice's. Once Alice receives this data, she can provision a new
key to her device, making a call to Provisioning Partner to
receive new credential information.
4. 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
5. Assumptions
* Original credential information (with cryptographic key material)
MUST NOT be sent or shared. Instead, sender SHALL be transferring
its approval token for Receiver to acquire new credential
information.
* Provisioning Partner SHALL NOT allow for two users to use the same
credential / cryptographic keys.
* Security: Communication between Sender / Receiver and Provisioning
Partner SHOULD be trusted.
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* The choice of intermediary SHALL be defined by the application
initiating the credential transfer.
* Sender and Receiver SHALL both be able to manage the shared
credential at any point by communicating with the Provisioning
Partner. Credential lifecycle management is out of scope for this
proposal.
* Any device OEM with a digital credential implementation adherent
to Tigress [Tigress-00] SHALL be able to receive shared
provisioning information, whether or not they can originate
provisioning information themselves or host their own
intermediary.
* Provisioning a credential on the Receiver MAY require multiple
round trips.
6. Requirements
* (Req-Connectivity) Sender and Receiver SHALL be allowed to be
online at different times. Sender and Receiver SHALL never need
to be online at the same time.
* (Req-init) Solution SHOULD allow Sender to send the share
invitation to Receiver over any messaging channel, with various
degrees of security.
* (Req-P2P) A goal of credential transfer covered in this document
SHALL include transfer from one device to another (group sharing
SHALL not be a goal).
* (Req-Security) Solution SHOULD provide security of the
provisioning data transferred (confidentiality, integrity and
availability).
* (Req-Revoke) Solution SHALL maintain access control, allowing
Sender to revoke before the share has been accepted, and for
Receiver to end transfer at any time.
* (Req-ArbitraryFormat) The solution SHALL support arbitrary message
formats to support both keys that implement public standards like
CCC as well as proprietary implementations of digital keys.
* (Req-UnderstoodFormat) Both Sender application and Receiver
application MUST be able to recognize the format.
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* (Req-RoundTrips) Solution SHALL allow for multiple round trips or
multiple reads/writes between one set of Sender and Receiver
devices.
* (Req-Preview) Solution SHOULD allow for extensibility and
discoverable extensions (preview of share invitation).
* (Req-RedemptionHandling) Shared Provisioning Information SHOULD
route Receiver to redeem Provisioning Information using the
designated Credential Management Application (e.g. Wallet).
6.1. 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-IntermediaryProvision) An Intermediary server MUST not be
able to provision credential on their own.
* (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.
7. 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
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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.
7.1. 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).
7.2. 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).
7.3. Signal Protocol
As a messaging protocol, Signal could be used between Sender,
Receiver and Intermediary but this protocol is fairly complex and its
use would most like violate (Req-Simplicity). The system will
however support the Signal service for share initiation, in line with
(Req-init).
8. Out of Scope
* Identification and Authorization - solution shall not require
strong identification and authentication from user (e.g. using PKI
certificates).
* Fully stopping people from sharing malicious content ("cat
pictures").
* Solving problem of sharing to groups.
* Detailing how credentials are provisioned either on a device or
with a provisioning partner.
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9. Security Considerations
TODO Security
10. IANA Considerations
This document has no IANA actions.
11. Normative References
[CCC-Digital-Key-30]
Car Connectivity Consortium, "Digital Key – The Future of
Vehicle Access", November 2021, <https://global-
carconnectivity.org/wp-content/uploads/2021/11/
CCC_Digital_Key_Whitepaper_Approved.pdf>.
[RFC2078] Linn, J., "Generic Security Service Application Program
Interface, Version 2", RFC 2078, DOI 10.17487/RFC2078,
January 1997, <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, March 1997,
<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, July 2005,
<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,
May 2017, <https://www.rfc-editor.org/rfc/rfc8174>.
[Tigress-00]
Vinokurov, D., Byington, M., Lerch, M., Pelletier, A., and
N. Sha, "Transfer Digital Credentials Securely", September
2022,
<https://datatracker.ietf.org/doc/draft-art-tigress/>.
Acknowledgments
TODO acknowledge.
Authors' Addresses
Dmitry Vinokurov
Apple Inc
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Email: dvinokurov@apple.com
Casey Astiz
Apple Inc
Email: castiz@apple.com
Alex Pelletier
Apple Inc
Email: a_pelletier@apple.com
Jean-Luc Giraud
Apple Inc
Email: jgiraud@apple.com
Alexey Bulgakov
Apple Inc
Email: abulgakov@apple.com
Matt Byington
Apple Inc
Email: mbyington@apple.com
Nick Sha
Alphabet Inc
Email: nicksha@google.com
Manuel Gerster
Mercedes-Benz AG
Email: manuel.gerster@mercedes-benz.com
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