Transfer Digital Credentials Securely
draft-vinokurov-tigress-http-00
| Document | Type | Active Internet-Draft (individual) | |
|---|---|---|---|
| Authors | Dmitry Vinokurov , Yogesh Karandikar , Matthias Lerch , Alex Pelletier , Nick Sha | ||
| Last updated | 2024-01-11 | ||
| RFC stream | (None) | ||
| Intended RFC status | (None) | ||
| Formats | |||
| Stream | Stream state | (No stream defined) | |
| Consensus boilerplate | Unknown | ||
| RFC Editor Note | (None) | ||
| IESG | IESG state | I-D Exists | |
| Telechat date | (None) | ||
| Responsible AD | (None) | ||
| Send notices to | (None) |
draft-vinokurov-tigress-http-00
Transfer dIGital cREdentialS Securely D. Vinokurov
Internet-Draft Y. Karandikar
Intended status: Standards Track M. Lerch
Expires: 14 July 2024 A. Pelletier
Apple Inc
N. Sha
Alphabet Inc
11 January 2024
Transfer Digital Credentials Securely
draft-vinokurov-tigress-http-00
Abstract
Digital Credentials allow users to access Homes, Cars or Hotels using
their mobile devices. Once a user has a Credential on a device,
sharing it to others is a natural use case. Process of sharing
credentials should be secure, privacy preserving and have a seamless
user experience. To facilitate Credential sharing, a new transport
is required. This document defines that new transport to meet unique
requirements of sharing a Credential.
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-vinokurov-tigress-http/.
Status information for this document may be found at
https://datatracker.ietf.org/doc/draft-vinokurov-tigress-http/.
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/dimmyvi/tigress.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Vinokurov, et al. Expires 14 July 2024 [Page 1]
Internet-Draft Tigress January 2024
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 14 July 2024.
Copyright Notice
Copyright (c) 2024 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 . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Conventions & Definitions . . . . . . . . . . . . . . . . . . 5
2.1. General Terms . . . . . . . . . . . . . . . . . . . . . . 5
3. Sharing Process . . . . . . . . . . . . . . . . . . . . . . . 6
3.1. Some Example Use Cases . . . . . . . . . . . . . . . . . 6
3.2. Credential Sharing Flow . . . . . . . . . . . . . . . . . 6
3.3. Relay Server Design Requirements . . . . . . . . . . . . 7
4. Relay Server Design . . . . . . . . . . . . . . . . . . . . . 8
4.1. Design Elements . . . . . . . . . . . . . . . . . . . . . 8
4.2. API connection details . . . . . . . . . . . . . . . . . 9
4.3. Sharing Flow With API calls . . . . . . . . . . . . . . . 9
5. HTTP Headers . . . . . . . . . . . . . . . . . . . . . . . . 13
5.1. Mailbox-Request-ID . . . . . . . . . . . . . . . . . . . 13
5.2. Mailbox-Device-Claim . . . . . . . . . . . . . . . . . . 13
5.3. Mailbox-Device-Attestation . . . . . . . . . . . . . . . 13
6. HTTP access methods . . . . . . . . . . . . . . . . . . . . . 13
6.1. CreateMailbox . . . . . . . . . . . . . . . . . . . . . . 14
6.1.1. Endpoint . . . . . . . . . . . . . . . . . . . . . . 14
6.1.2. Request Parameters: . . . . . . . . . . . . . . . . . 14
6.1.3. Consumes . . . . . . . . . . . . . . . . . . . . . . 14
Vinokurov, et al. Expires 14 July 2024 [Page 2]
Internet-Draft Tigress January 2024
6.1.4. Produces . . . . . . . . . . . . . . . . . . . . . . 14
6.1.5. Request body . . . . . . . . . . . . . . . . . . . . 14
6.1.6. Responses . . . . . . . . . . . . . . . . . . . . . . 17
6.2. UpdateMailbox . . . . . . . . . . . . . . . . . . . . . . 17
6.2.1. Endpoint . . . . . . . . . . . . . . . . . . . . . . 18
6.2.2. Request Parameters . . . . . . . . . . . . . . . . . 18
6.2.3. Consumes . . . . . . . . . . . . . . . . . . . . . . 18
6.2.4. Produces . . . . . . . . . . . . . . . . . . . . . . 18
6.2.5. Request body . . . . . . . . . . . . . . . . . . . . 18
6.2.6. Responses . . . . . . . . . . . . . . . . . . . . . . 19
6.3. DeleteMailbox . . . . . . . . . . . . . . . . . . . . . . 20
6.3.1. Endpoint . . . . . . . . . . . . . . . . . . . . . . 20
6.3.2. Request Parameters . . . . . . . . . . . . . . . . . 20
6.3.3. Responses . . . . . . . . . . . . . . . . . . . . . . 21
6.4. ReadDisplayInformationFromMailbox . . . . . . . . . . . . 21
6.4.1. Endpoint . . . . . . . . . . . . . . . . . . . . . . 21
6.4.2. Request Parameters . . . . . . . . . . . . . . . . . 21
6.4.3. Produces . . . . . . . . . . . . . . . . . . . . . . 21
6.4.4. Responses . . . . . . . . . . . . . . . . . . . . . . 21
6.5. ReadSecureContentFromMailbox . . . . . . . . . . . . . . 22
6.5.1. Endpoint . . . . . . . . . . . . . . . . . . . . . . 22
6.5.2. Request Parameters . . . . . . . . . . . . . . . . . 22
6.5.3. Produces . . . . . . . . . . . . . . . . . . . . . . 23
6.5.4. Responses . . . . . . . . . . . . . . . . . . . . . . 23
6.6. RelinquishMailbox . . . . . . . . . . . . . . . . . . . . 24
6.6.1. Endpoint . . . . . . . . . . . . . . . . . . . . . . 24
6.6.2. Request Parameters . . . . . . . . . . . . . . . . . 24
6.6.3. Responses . . . . . . . . . . . . . . . . . . . . . . 24
7. Provisioning Information Structure . . . . . . . . . . . . . 25
7.1. Provisioning Information Format . . . . . . . . . . . . . 25
7.2. Provisioning Information Encryption . . . . . . . . . . . 26
7.3. Share URL . . . . . . . . . . . . . . . . . . . . . . . . 27
7.3.1. Credential Vertical in Share URL . . . . . . . . . . 28
8. Security Considerations . . . . . . . . . . . . . . . . . . . 29
8.1. Relay Server defined in this document . . . . . . . . . . 29
8.1.1. Confidentiality & Integrity . . . . . . . . . . . . . 29
8.1.2. Network attacks . . . . . . . . . . . . . . . . . . . 29
8.1.3. Privacy Considerations . . . . . . . . . . . . . . . 29
8.2. Clients of Relay Server . . . . . . . . . . . . . . . . . 30
8.2.1. Confidentiality & Integrity . . . . . . . . . . . . . 30
8.2.2. Privacy Considerations . . . . . . . . . . . . . . . 30
8.3. Overall System . . . . . . . . . . . . . . . . . . . . . 31
8.3.1. Initiator shares with the wrong Recipient . . . . . . 31
8.3.2. Malicious Recipient forwards the share to 3rd party
without redeeming it or the Recipient's device is
compromised. . . . . . . . . . . . . . . . . . . . . 31
8.3.3. Invitation Channel Security . . . . . . . . . . . . . 31
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 32
Vinokurov, et al. Expires 14 July 2024 [Page 3]
Internet-Draft Tigress January 2024
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 32
10.1. Normative References . . . . . . . . . . . . . . . . . . 32
10.2. Informative References . . . . . . . . . . . . . . . . . 33
Appendix A. Contributors . . . . . . . . . . . . . . . . . . . . 33
Appendix B. Acknowledgments . . . . . . . . . . . . . . . . . . 33
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 34
1. Introduction
Mobile devices with ever increasing computational power and security
capabilities are enabling various use cases. One such category
includes use of mobile devices to gain access to a property that a
user owns or rents or is granted access to. The cryptographic
material and other data required to enable this use case is termed as
Digital Credential.
Based on type of property, various public or proprietary standards
govern details of Digital Credentials. These sets of standards and
the bodies setting them are collectively termed as Verticals. The
details include policies, mechanism and practices to create, maintain
and use Digital Credentials. The process of getting a Digital
Credential on a mobile device is termed as Provisioning.
Once a user has a Digital Credential provisioned on their mobile
device, sharing it to others is a natural use case. Sharing a
Credential should feel like a natural extension of regular
communication methods (like instant messaging, sms, email). The user
experience of sharing a Credential should be intuitive, similar to
sharing other digital assets like photos or documents. The sharing
process should be secure and privacy preserving.
Credentials pose two unique requirements that differ from sharing
other digital assets. The Initiator and Recipient devices may need
to communicate back and forth to transfer the necessary Provisioning
Information. The Provisioning Information exchange must be limited
to Initiator device and the first Recipient device to claim the
information.
To achieve these goals, a new transport is necessary. This document
defines HTTP [RFC9110] based API to create such a transport, termed
as Relay Server. The document also defines data in JSON standard
[RFC8259] to enable a uniform user experience for securely sharing
Digital Credentials of various types.
Vinokurov, et al. Expires 14 July 2024 [Page 4]
Internet-Draft Tigress January 2024
2. Conventions & 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.
2.1. General Terms
* Digital Credential (or simply Credential) - Cryptographic material
and other data used to authorize User with an access point. The
cryptographic material can also be used for mutual authentication
between user device and access point.
* Digital Credential Vertical (or simply Vertical) - The public or
proprietary standards that that define details of Digital
Credentials for type of property accessed. The details include
policy, process and mechanism to create, maintain and use Digital
Credentials in the given Vertical.
* Provisioning - A Vertical defined process of adding a new Digital
Credential to the device.
* Provisioning Entity - An entity that facilitates creation, update
and termination (Lifecycle Management) of the Credential. Based
on Vertical, the role of Provisioning Entity may be played by
various actors in various stages of Credential lifecycle.
* Provisioning Information - data transferred from Initiator to
Recipient that is both necessary and sufficient for the Recipient
to Provision a Credential.
* Initiator - User and their device initiating a transfer of
Provisioning Information to a Recipient.
* Recipient - User and their device that receives Provisioning
Information and uses it to provision a new Credential.
* Relay Server - an intermediary server that provides a standardized
and platform-independent way of transferring Provisioning
Information between Initiator and Recipient, acting as a temporary
store and forward service. This is the new transport defined by
this document.
* Secret - a symmetric encryption key shared between an Initiator
and Recipient device. It is used to encrypt Provisioning
Information stored on the Relay server.
Vinokurov, et al. Expires 14 July 2024 [Page 5]
Internet-Draft Tigress January 2024
3. Sharing Process
3.1. Some Example Use Cases
* Amit owns a car that supports Digital Credentials. Being a tech
enthusiast, he has the Credential provisioned on his mobile
device. Amit can now use his mobile device to lock/unlock and
operate his car. One Monday he is out of town and realizes that
his car needs to be moved for street cleaning. He asks his
neighbor Bob for help via their favorite instant messaging method.
As Bob agrees, Amit shares the Digital Credential to Bob via the
next instant message. Bob accepts the Credential and uses his
mobile device to unlock Amit's car and drive it to the other side
of street.
* Alice booked a room at a hotel that supports Digital Credentials.
Being a frequent traveller, she has the Digital Credential
provisioned on her mobile device. As her flight gets delayed, she
realizes that her partner Bakari will reach the hotel first. So
she shares the Digital Credential with him over email. Bakari
sees the email after his flight lands and he accepts the shared
Credential. On his arrival to the hotel, Bakari is able to access
common areas and their room using his mobile device.
3.2. Credential Sharing Flow
A simplified sharing flow is shown in the sequence diagram below.
Initiator (User) sends an invitation to share a Credential over their
preferred communication method. Recipient (user) accepts the
Credential share invitation. Then the two devices go back and forth
as necessary to transfer Provisioning Information without further
interaction by user. After the transfer is complete Recipient device
gets the Credential Provisioned according to Vertical defined
process.
┌─┐ ┌─┐
║"│ ║"│
└┬┘ └┬┘
┌┼┐ ┌┼┐
│ ┌────────────────┐ ┌────────────┐ ┌────────────────┐ │
┌┴┐ │Initiator Device│ │Relay Server│ │Recipient Device│ ┌┴┐
Initiator User └───────┬────────┘ └─────┬──────┘ └───────┬────────┘ Recipient User
│ Initiate Credential Share│ │ │ │
│ ─────────────────────────> │ │ │
│ │ │ │ │
│ │ create a mailbox, establish Initiator claim│ │ │
│ │ ───────────────────────────────────────────> │ │
│ │ │ │ │
Vinokurov, et al. Expires 14 July 2024 [Page 6]
Internet-Draft Tigress January 2024
│ │ Invitation to accept Credential │ │
│ │ over IM, sms, email etc │ │
│ │ ─────────────────────────────────────────────────────────────────────────────> │
│ │ │ │ │
│ │ │ │ accept the Credential │
│ │ │ │ <─────────────────────────
│ │ │ │ │
│ │ │ establish Recipient claim │ │
│ │ │ <──────────────────────────────── │
│ │ │ │ │
│ │ │ │ │
│ ╔═══════╤═════════╪════════════════════════════════════════════╪═════════════════════════════════╪══════════════════╗ │
│ ║ LOOP │ Transfer │ │ ║ │
│ ╟───────┘ │ │ │ ║ │
│ ║ │ │ request Provisioning Information│ ║ │
│ ║ │ │ <──────────────────────────────── ║ │
│ ║ │ │ │ ║ │
│ ║ │ Forward request │ │ ║ │
│ ║ │ <─────────────────────────────────────────── │ ║ │
│ ║ │ │ │ ║ │
│ ║ │ Provisioning Information response │ │ ║ │
│ ║ │ ───────────────────────────────────────────> │ ║ │
│ ║ │ │ │ ║ │
│ ║ │ │ forward response │ ║ │
│ ║ │ │ ────────────────────────────────> ║ │
│ ╚═════════════════╪════════════════════════════════════════════╪═════════════════════════════════╪══════════════════╝ │
│ │ │ │ │
│ │ │ ╔═══════════════╧════════════════╗ │
│ │ │ ║Finish Credential Provisioning ░║ │
Initiator User ┌───────┴────────┐ ┌─────┴──────┐ ╚════════════════════════════════╝ Recipient User
┌─┐ │Initiator Device│ │Relay Server│ │Recipient Device│ ┌─┐
║"│ └────────────────┘ └────────────┘ └────────────────┘ ║"│
└┬┘ └┬┘
┌┼┐ ┌┼┐
│ │
┌┴┐ ┌┴┐
3.3. Relay Server Design Requirements
Based on the sharing flow, we can see that Relay server is an
important component of the credential Sharing flow. Relay server
design needs to adhere to following requirements :
* Relay server SHALL provide confidentiality and integrity to the
transfer of Provisioning Information.
Vinokurov, et al. Expires 14 July 2024 [Page 7]
Internet-Draft Tigress January 2024
* Transfer of Provisioning Information MAY require several round
trips. Relay server SHALL guarantee round trip communication
between initiator device and first device to establish Recipient
claim.
* Relay Server SHALL support flow of information that MAY NOT always
be in turn taking fashion. Same party SHALL be allowed to send
back to back messages. E.g. a cancel message may be sent by same
party that sent the previous message.
* User involvement in the process needs to be minimal for a seamless
user experience. A lay user is expected to be unaware of Relay
Server (similar to any transport protocols like TCP/IP). So Relay
Server SHALL be able to function without user interaction.
* Initiator and Recipient MAY NOT be online at the same time. So
Relay Server SHALL be able to store and forward data. It is
RECOMMENDED to have notification mechanism for snappy user
experience.
* To protect user privacy, Relay server SHALL NOT require any
identifying information of the 2 parties involved in the transfer.
* Relay Server SHALL allow encrypted data (that can not be
deciphered by the Relay Server itself) to be stored and
transferred.
* Relay Server MAY host multiple mailboxes at the same time, each
bound to various pairs of Initiator and Recipient Devices. Relay
Server SHALL not be able to relate the devices across various
mailboxes.
* User preferred communication methods need to be allowed for
invitation delivery. It's assumed that user is familiar with them
and trusts them to be secure enough to deliver messages to
intended recipient. But security properties of the methods can
not be taken for granted in the design of the Relay Server.
Verticals can require second factor to authenticate Recipient if
they deem it necessary. Policies and mechanisms for this second
factor are in the realm of the Verticals and outside the scope of
this document.
4. Relay Server Design
4.1. Design Elements
* Mailbox - A place to store data on the Relay Server. A reader can
also read the data from mailbox.
Vinokurov, et al. Expires 14 July 2024 [Page 8]
Internet-Draft Tigress January 2024
* MailboxIdentifier - a unique identifier for the given mailbox,
generated by the Relay server at the time of mailbox creation.
The value is a UUID [RFC4122].
* Device Claim - a unique token allowing the caller to read from /
write data to the mailbox. Initiator Device generates a Device
Claim and presents it to the Relay Server at time of mailbox
creation. Relay server creates a mailbox, and binds it to
Initiator's Device Claim. Recipient Device generates a Device
Claim and presents it to the Relay Server, at time of first read
from mailbox. Relay server binds the mailbox to the Recipient's
Device Claim. Thus, both Initiator and Recipient devices are
bound to the mailbox (allowed to read from / write to it). Only
Initiator and Recipient devices that present valid Device Claims
are allowed to send subsequent read/update/delete calls to the
mailbox. The value SHALL be a unique UUID [RFC4122]. Initiator
and Recipient MUST use different values for Device Claim.
Implementation SHOULD assign unique values for new mailboxes
(avoid re-using values).
* Notification Token - a short or long-lived unique token stored by
the Initiator or Recipient Device in a mailbox on the Relay
server. This allows Relay server to send a push notification to
the Initiator or Recipient Device, informing them of updates in
the mailbox.
4.2. API connection details
The Relay server API endpoint MUST be accessed over HTTP using an
https URI [RFC2818] and SHOULD use the default https port. This
ensures confidentiality property of the transfer process.
Request and response bodies SHALL be formatted as either JSON or HTML
(based on the API endpoint). The communication protocol used for all
interfaces SHALL be HTTPs.
All Strings SHOULD be UTF-8 encoded (Unicode Normalization Form C
(NFC)).
An API version SHOULD be included in the URI for all interfaces. The
version at the time of this document's latest update is v1. The
version SHALL be incremented by 1 for major API changes or backward
incompatible iterations on existing APIs.
4.3. Sharing Flow With API calls
Sequence diagram below shows an example sharing flow with detailed
API calls.
Vinokurov, et al. Expires 14 July 2024 [Page 9]
Internet-Draft Tigress January 2024
* Initiator Device composes Provisioning Information and encrypts it
with a Secret before storing it in a mailbox on Relay Server
* Initiator Device generates a unique token - an Initiator Device
Claim - to be sent to Relay Server. Initiator Device Claim allows
the Initiator Device to read and write data to / from the mailbox,
thus binding it to the mailbox.
* Initiator Device can also create an optional notification token
for the mailbox with the Relay Server. Relay Server can notify
Initiator devices when other side has deposited data in mailbox
that is ready to be read. This improves user experience over
polling mechanism that the devices would have to use otherwise.
* Initiator Device calls CreateMailbox API endpoint on a Relay
server and provides Device Claim and optional Notification token.
Relay server creates the mailbox and assigns a unique Mailbox
Identifier generated using a good source of entropy (preferably
hardware-based entropy).
* A mailbox has limited lifetime configured with mandatory
"expiration" parameter in mailboxConfiguration. When expired, the
mailbox SHALL be deleted - refer to DeleteMailbox endpoint. Relay
server SHALL be responsible to periodically check for mailboxes
that are past the expiration time and delete them.
* Relay server builds a unique URL link to a mailbox (for example,
“https://relayserver.example.com/v1/m/1234567890”) and returns it
to the Initiator Device.
* Initiator sends this link as invitation to Recipient Device over
communication method preferred by users.
* Recipient Device, having obtained both the URL link and the
Secret, is ready to read the mailbox upon user action.
* Recipient Device generates a unique token - a Recipient Device
Claim - to be sent to Relay Server. Recipient Device Claim allows
the Recipient Device to read and write data to / from the mailbox,
thus binding it to the mailbox.
* Recipient Device can also create an optional notification token
for the mailbox with the Relay Server for snappy user experience.
Vinokurov, et al. Expires 14 July 2024 [Page 10]
Internet-Draft Tigress January 2024
* Recipient Device calls ReadSecureContentFromMailbox API endpoint
on the Relay Server and provides Device Claim and optional
Notification token. If this is the first Recipient claim, Relay
server allows the read and binds the device to the mailbox. Thus
establishing a connection between Initiator and Recipient devices
facilitated by Relay Server.
* Initiator Device or bound Recipient Device may delete the mailbox
using the DeleteMailbox API call.
┌─┐ ┌─┐
║"│ ║"│
└┬┘ └┬┘
┌┼┐ ┌┼┐
│ ┌────────────────┐ ┌────────────┐ ┌────────────────┐ │
┌┴┐ │Initiator Device│ │Relay Server│ │Recipient Device│ ┌┴┐
Initiator User └───────┬────────┘ └─────┬──────┘ └───────┬────────┘ Recipient User
│ Share this Credential with Recipient User│ │ │ │
│ over communication method m_1 │ │ │ │
│ ─────────────────────────────────────────> │ │ │
│ │ │ │ │
│ ╔══════════════════╧═══════════════════╗ │ │ │
│ ║Create and encrypt Provisioning ░║ │ │ │
│ ║Info message_1 encrypted with Secret ║ │ │ │
│ ╚══════════════════╤═══════════════════╝ │ │ │
│ │ CreateMailbox │ │ │
│ │ (With DeviceClaim and Notification token)│ │ │
│ │ ─────────────────────────────────────────> │ │
│ │ │ │ │
│ │ URL link to mailbox │ │ │
│ │ <───────────────────────────────────────── │ │
│ │ │ │ │
│ │ URL link and Secret │ │ │
│ │ over preferred communication method m_1 │ │
│ │ ────────────────────────────────────────────────────────────────────────> │
│ │ │ │ │
│ │ │ │ Accept the Credential │
│ │ │ │ <─────────────────────────
│ │ │ │ │
│ │ │ ReadSecureContentFromMailbox │ │
│ │ │ (With DeviceClaim) │ │
│ │ │ <───────────────────────────── │
│ │ │ │ │
│ │ │ encrypted info │ │
│ │ │ ─────────────────────────────> │
│ │ │ │ │
│ │ │ ╔═══════════════════════════╧══════════════════════════╧═╗
│ │ │ ║Decrypt with Secret to get Provisioning Info message_1 ░║
Vinokurov, et al. Expires 14 July 2024 [Page 11]
Internet-Draft Tigress January 2024
│ │ │ ╚═══════════════════════════╤══════════════════════════╤═╝
│ │ │ ╔════════════════╧══════════════════╗ │
│ │ │ ║Generate Provision Info message_2 ░║ │
│ │ │ ║encrypted with Secret ║ │
│ │ │ ╚════════════════╤══════════════════╝ │
│ │ │ UpdateMailbox(encrypted info)│ │
│ │ │ <───────────────────────────── │
│ │ │ │ │
│ │ │ OK │ │
│ │ │ ─────────────────────────────> │
│ │ │ │ │
│ │ Push Notification │ │ │
│ │ <───────────────────────────────────────── │ │
│ │ │ │ │
│ │ ReadSecureContentFromMailbox │ │ │
│ │ ─────────────────────────────────────────> │ │
│ │ │ │ │
│ │ encrypted info │ │ │
│ │ <───────────────────────────────────────── │ │
│ │ │ │ │
│ ╔═════════════════════════╧═══════════════════════════╗ │ │ │
│ ║Decrypt with Secret to get Provision Info message_2 ░║ │ │ │
│ ╚═════════════════════════╤═══════════════════════════╝ │ │ │
│ ╔══════════════════╧═══════════════════╗ │ │ │
│ ║Update with Provision Info message_3 ░║ │ │ │
│ ║encrypted with Secret ║ │ │ │
│ ╚══════════════════╤═══════════════════╝ │ │ │
│ │ UpdateMailbox(encrypted info) │ │ │
│ │ ─────────────────────────────────────────> │ │
│ │ │ │ │
│ │ OK │ │ │
│ │ <───────────────────────────────────────── │ │
│ │ │ │ │
│ │ │ Push Notification │ │
│ │ │ ─────────────────────────────> │
│ │ │ │ │
│ │ │ ReadSecureContentFromMailbox │ │
│ │ │ <───────────────────────────── │
│ │ │ │ │
│ │ │ encrypted info │ │
│ │ │ ─────────────────────────────> │
│ │ │ │ │
│ │ ╔════════╧══════════════════════════════╧══════════╗ │
│ │ ║Decrypt with Secret for Provision Info message_3 ░║ │
│ │ ╚════════╤══════════════════════════════╤══════════╝ │
│ │ │ DeleteMailbox │ │
│ │ │ <───────────────────────────── │
│ │ │ │ │
Vinokurov, et al. Expires 14 July 2024 [Page 12]
Internet-Draft Tigress January 2024
│ │ │ OK │ │
│ │ │ ─────────────────────────────> │
│ │ │ │ │
│ │ │ ╔═══════════════╧════════════════╗ │
│ │ │ ║Finish Credential Provisioning ░║ │
Initiator User ┌───────┴────────┐ ┌─────┴──────┐ ╚════════════════════════════════╝ Recipient User
┌─┐ │Initiator Device│ │Relay Server│ │Recipient Device│ ┌─┐
║"│ └────────────────┘ └────────────┘ └────────────────┘ ║"│
└┬┘ └┬┘
┌┼┐ ┌┼┐
│ │
┌┴┐ ┌┴┐
5. HTTP Headers
5.1. Mailbox-Request-ID
All requests to and from Relay server will have an HTTP header
"Mailbox-Request-ID". The corresponding response to the API will
have the same HTTP header, which SHALL echo the value in the request
header. This is used to identify the request associated to the
response for a particular API request and response pair. The value
SHOULD be a UUID [RFC4122]. The request originator SHALL match the
value of this header in the response with the one sent in the
request. If response is not received, caller may retry sending the
request with the same value of "Mailbox-Request-ID". Relay server
SHOULD store the value of the last successfully processed "Mailbox-
Request-ID" for each device based on the caller's Device Claim. A
key-value pair of "Device Claim" to "Mailbox-Request-ID" is suggested
to store the last successfully processed request for each device. In
case of receiving a request with duplicated "Mailbox-Request-ID",
Relay SHOULD respond to the caller with status code 201, ignoring the
duplicate request body content.
5.2. Mailbox-Device-Claim
All requests to CreateMailbox, ReadSecureContentFromMailbox and
UpdateMailbox endpoints MUST contain this header. The value
represents "Device Claim" (refer to Terminology)
5.3. Mailbox-Device-Attestation
Request to CreateMailbox MAY contain this header. The value
represents a Device Attestation (String, Optional) - optional remote
OEM device proprietary attestation data
6. HTTP access methods
Vinokurov, et al. Expires 14 July 2024 [Page 13]
Internet-Draft Tigress January 2024
6.1. CreateMailbox
An application running on a remote device can invoke this API on
Relay Server to create a mailbox and store secure data content to it
(encrypted data specific to a provisioning partner).
MailboxIdentifier is created by the Relay server as an UUID
[RFC4122], using cryptographic entropy. A URL to the created mailbox
to be returned to the caller in the response.
6.1.1. Endpoint
POST /{version}/m
6.1.2. Request Parameters:
Path parameters
* version (String, Required) - the version of the API. At the time
of writing this document, “v1”.
Header parameters
* Mailbox-Device-Attestation (String, Optional) - optional remote
OEM device proprietary attestation data.
* Mailbox-Device-Claim (String, UUID, Required) - Device Claim
(refer to Terminology).
* Mailbox-Request-ID (String, UUID, Required) - Unique request
identifier.
6.1.3. Consumes
This API call consumes the following media types via the Content-Type
request header: application/json
6.1.4. Produces
This API call produces the following media types via the Content-Type
response header: application/json
6.1.5. Request body
Request body is a complex structure, including the following fields:
Vinokurov, et al. Expires 14 July 2024 [Page 14]
Internet-Draft Tigress January 2024
* payload (Object, Required) - for the purposes of Tigress API, this
is a data structure, describing Provisioning Information specific
to Credential Provider. It consists of the following 2 key-value
pairs:
1. "type": "AEAD_AES_128_GCM" (refer to Encryption Format
section).
2. "data": BASE64-encoded binary value of ciphertext.
* displayInformation (Object, Required) - for the purposes of the
Tigress API, this is a data structure. It allows an application
running on a receiving device to build a visual representation of
the credential to show to user. The data structure contains the
following fields:
1. title (String, Required) - the title of the credential (e.g.
"Car Key")
2. description (String, Required) - a brief description of the
credential (e.g. "a key to my personal car")
3. imageURL (String, Required) - a link to a picture representing
the credential visually.
* notificationToken (Object, Optional) - optional notification token
used to notify an appropriate remote device that the mailbox data
has been updated. Data structure includes the following (if
notificationToken is provided it should include both fields):
1. type (String, Required) - notification token name. Used to
define which Push Notification System to be used to notify
appropriate remote device of a mailbox data update. (E.g.
"com.apple.apns" for APNS)
2. tokenData (String, Required) - notification token data (data
encoded based on specific device OEM notification service
rules - e.g. HEX-encoded or Base64-encoded) - application-
specific - refer to appropriate Push Notification System
specification.
* mailboxConfiguration (Object, Optional) - optional mailbox
configuration, defines access rights to the mailbox, mailbox
expiration time. Required at the time of the mailbox creation.
OEM device may provide this data in the request, Relay server
shall define a default configuration, if it is not provided in the
incoming request. Data structure includes the following:
Vinokurov, et al. Expires 14 July 2024 [Page 15]
Internet-Draft Tigress January 2024
1. accessRights (String, Optional) - optional access rights to
the mailbox for Initiator and Recipient devices. Default
access to the mailbox is Read and Delete. Value is defined as
a combination of the following values: "R" - for read access,
"W" - for write access, "D" - for delete access. Example"
"RD" - allows to read from the mailbox and delete it.
2. expiration (String, Required) - Mailbox expiration time in
"YYYY-MM-DDThh:mm:ssZ" format (UTC time zone) [RFC3339].
Mailbox has limited lifetime. Once expired, it SHALL be
deleted - refer to DeleteMailbox endpoint. Relay server
SHOULD periodically check for expired mailboxes and delete
them.
{
"notificationToken": {
"type":"com.apple.apns",
"tokenData":"APNS1234...QW"
}
}
Figure 1: Apple Push Token Example
{
"displayInformation" : {
"title" : "Hotel Pass",
"description" : "Some Hotel Pass",
"imageURL" : "https://example.com/sharingImage"
},
"payload" : {
"type": "AEAD_AES_128_GCM",
"data": "FDEC...987654321"
},
"notificationToken" : {
"type" : "com.apple.apns",
"tokenData" : “APNS...1234"
},
"mailboxConfiguration" : {
"accessRights" : "RWD",
"expiration" : "2022-02-08T14:57:22Z"
}
}
Figure 2: Create Mailbox Request Example
Vinokurov, et al. Expires 14 July 2024 [Page 16]
Internet-Draft Tigress January 2024
6.1.6. Responses
200 Status: “200” (OK)
ResponseBody:
* urlLink (String, Required) - a full URL link to the mailbox
including fully qualified domain name and mailbox Identifier.
Refer to "Share URL" section for details.
* isPushNotificationSupported (boolean, Required) - indicates
whether push notification is supported or not. The device uses
this field to decide whether it should listen on the push topic or
do long-polling.
{
"urlLink":"https://relayserver.example.com/m/12345678-9...A-BCD",
"isPushNotificationSupported":true
}
Figure 3: Create Mailbox Response Example
201 Status: “201” (Created) - response to a duplicated request
(duplicated "Mailbox-Request-ID"). Relay server SHALL respond to
duplicated requests with 201 without creating a new mailbox.
"Mailbox-Request-ID" passed in the first CreateMailbox request's
header SHOULD be stored by the Relay server and compared to the same
value in the subsequent requests to identify duplicated requests. If
duplicate is found, Relay SHALL not create a new mailbox, but respond
with 201 instead. The value of "Mailbox-Request-ID" of the last
successfully completed request SHOULD be stored based on the Device
Claim passed by the caller.
400 Bad Request - invalid request has been passed (can not parse or
required fields missing).
401 Unauthorized - calling device is not authorized to create a
mailbox. E.g. a device presented an invalid device claim or device
attestation.
6.2. UpdateMailbox
An application running on a remote device can invoke this API on
Relay Server to update secure data content in an existing mailbox
(encrypted data specific to a Provisioning Partner). The update
effectively overwrites the secure payload previously stored in the
mailbox.
Vinokurov, et al. Expires 14 July 2024 [Page 17]
Internet-Draft Tigress January 2024
6.2.1. Endpoint
PUT /{version}/m/{mailboxIdentifier}
6.2.2. Request Parameters
Path parameters:
* version (String, Required) - the version of the API. At the time
of writing this document, “v1”.
* mailboxIdentifier(String, Required) - MailboxIdentifier (refer to
Terminology).
Header parameters:
* Mailbox-Device-Attestation (String, Optional) - optional remote
OEM device proprietary attestation data.
* Mailbox-Device-Claim (String, UUID, Required) - Device Claim
(refer to Terminology).
* Mailbox-Request-ID (String, UUID, Required) - Unique request
identifier.
6.2.3. Consumes
This API call consumes the following media types via the Content-Type
request header: application/json
6.2.4. Produces
This API call produces following media types via the Content-Type
request header: application/json
6.2.5. Request body
Request body is a complex structure, including the following fields:
* payload (Object, Required) - for the purposes of Tigress API, this
is a data structure, describing Provisioning Information specific
to Credential Provider. It consists of the following 2 key-value
pairs:
1. "type": "AEAD_AES_128_GCM" (refer to Encryption Format
section).
2. "data": BASE64-encoded binary value of ciphertext.
Vinokurov, et al. Expires 14 July 2024 [Page 18]
Internet-Draft Tigress January 2024
* notificationToken (Object, Optional) - optional notification token
used to notify an appropriate remote device that the mailbox data
has been updated. Data structure includes the following (if
notificationToken is provided it should include both fields):
1. type (String, Required) - notification token name. Used to
define which Push Notification System to be used to notify
appropriate remote device of a mailbox data update. (E.g.
"com.apple.apns" for APNS)
2. tokenData (String, Required) - notification token data (data
encoded based on specific device OEM notification service
rules - e.g. HEX-encoded or Base64-encoded) - application-
specific - refer to appropriate Push Notification System
specification.
{
"payload" : {
"type": "AEAD_AES_128_GCM",
"data": "FDEC...987654321"
},
"notificationToken":{
"type" : "com.apple.apns",
"tokenData" : “APNS...1234"
}
}
Figure 4: Update Mailbox Request Example
6.2.6. Responses
ResponseBody:
* isPushNotificationSupported (boolean, Required) - indicates
whether push notification is supported or not. The device uses
this field to decide whether it should listen on the push topic or
do long-polling.
{
"isPushNotificationSupported":true
}
Figure 5: Update Mailbox Response Example
200 Status: “200” (OK)
Vinokurov, et al. Expires 14 July 2024 [Page 19]
Internet-Draft Tigress January 2024
201 Status: “201” (Created) - response to a duplicate request
(duplicate "Mailbox-Request-ID"). Relay server SHALL respond to
duplicate requests with 201 without performing mailbox update.
"Mailbox-Request-ID" passed in the first UpdateMailbox request's
header SHALL be stored by the Relay server and compared to the same
value in the subsequent requests to identify duplicate requests. If
duplicate is found, Relay SHALL not perform mailbox update, but
respond with 201 instead. The value of "Mailbox-Request-ID" of the
last successfully completed request SHALL be stored based on the
Device Claim passed by the caller.
400 Bad Request - invalid request has been passed (can not parse or
required fields missing).
401 Unauthorized - calling device is not authorized to update the
mailbox. E.g. a device presented the incorrect Device Claim.
404 Not Found - mailbox with provided mailboxIdentifier not found.
6.3. DeleteMailbox
An application running on a remote device can invoke this API on
Relay Server to close the existing mailbox after it served its
purpose. Recipient or Initiator Device needs to present a Device
Claim in order to close the mailbox.
6.3.1. Endpoint
DELETE /{version}/m/{mailboxIdentifier}
6.3.2. Request Parameters
Path parameters:
* version (String, Required) - the version of the API. At the time
of writing this document, “v1”.
* mailboxIdentifier(String, Required) - MailboxIdentifier (refer to
Terminology).
Header parameters:
* Mailbox-Device-Claim (String, UUID, Required) - Device Claim
(refer to Terminology).
* Mailbox-Request-ID (String, UUID, Required) - Unique request
identifier.
Vinokurov, et al. Expires 14 July 2024 [Page 20]
Internet-Draft Tigress January 2024
6.3.3. Responses
200 Status: “200” (OK)
401 Unauthorized - calling device is not authorized to delete a
mailbox. E.g. a device presented the incorrect Device Claim.
404 Not Found - mailbox with provided mailboxIdentifier not found.
Relay server may respond with 404 if the Mailbox Identifier passed by
the caller is invalid or mailbox has already been deleted (as a
result of duplicate DeleteMailbox request).
6.4. ReadDisplayInformationFromMailbox
An application running on a remote device can invoke this API on
Relay Server to retrieve public display information content from a
mailbox. Display Information shall be returned in OpenGraph format
(please refer to https://ogp.me for details). OpenGraph-formatted
display information is required to display a preview of credential in
a messaging application, e.g. iMessage or WhatsApp.
6.4.1. Endpoint
GET /{version}/m/{mailboxIdentifier}
6.4.2. Request Parameters
Path parameters:
* version (String, Required)- the version of the API. At the time
of writing this document, “v1”.
* mailboxIdentifier(String, Required) - MailboxIdentifier (refer to
Terminology).
6.4.3. Produces
This API call produces the following media types via the Content-Type
response header: text/html
6.4.4. Responses
200 Status: “200” (OK)
ResponseBody :
Vinokurov, et al. Expires 14 July 2024 [Page 21]
Internet-Draft Tigress January 2024
* displayInformation (Object, Required) - visual representation of
digital credential in OpenGraph format (please refer to
https://ogp.me for details).
"<html prefix="og: https://ogp.me/ns#">
<head>
<title>Hotel Pass</title>
<meta property="og:title" content="Hotel Pass" />
<meta property="og:type" content="image/jpeg" />
<meta property="og:description" content="Some Hotel Pass" />
<meta property="og:url" content="share://" />
<meta property="og:image" content="https://example.com/photos/photo.jpg" />
<meta property="og:image:width" content="612" />
<meta property="og:image:height" content="408" /></head>
</html>"
Figure 6: Read Display Information Response Example
404 Not Found - mailbox with provided mailboxIdentifier not found.
6.5. ReadSecureContentFromMailbox
An application running on a remote device can invoke this API on
Relay Server to retrieve secure payload content from a mailbox
(encrypted data specific to a Provisioning Information Provider).
6.5.1. Endpoint
POST /{version}/m/{mailboxIdentifier}
6.5.2. Request Parameters
Path parameters:
* version (String, Required) - the version of the API. At the time
of writing this document, “v1”.
* mailboxIdentifier(String, Required) - MailboxIdentifier (refer to
Terminology).
Header parameters:
* Mailbox-Device-Claim (String, UUID, Required) - Device Claim
(refer to Terminology).
Vinokurov, et al. Expires 14 July 2024 [Page 22]
Internet-Draft Tigress January 2024
6.5.3. Produces
This API call produces the following media types via the Content-Type
response header: application/json
6.5.4. Responses
200 Status: “200” (OK)
ResponseBody :
* payload (String, Required) - for the purposes of Tigress API, this
is a JSON metadata blob, describing Provisioning Information
specific to Credential Provider.
* displayInformation (Object, Required) - for the purposes of the
Tigress API, this is a JSON data blob. It allows an application
running on a receiving device to build a visual representation of
the credential to show to user. Specific to Credential Provider.
* expiration (String, Required) - the date that the mailbox will
expire. The mailbox expiration time is set during mailbox
creation. Expiration time should be a complete [RFC3339] date
string in "YYYY-MM-DDThh:mm:ssZ" format (UTC time zone), and can
be used to allow receiving clients to show when a share will
expire.
{
“displayInformation" : {
"title" : "Hotel Pass",
"description" : "Some Hotel Pass",
"imageURL" : "https://example.com/sharingImage"
},
"payload" : {
"type": "AEAD_AES_128_GCM",
"data": "FDEC...987654321"
},
"expiration": "2021-11-03T20:32:34Z"
}
Figure 7: Read Secure Content Response Example
401 Unauthorized - calling device is not authorized to read the
secure content of the mailbox. E.g. a device presented the incorrect
Device Claim.
404 Not Found - mailbox with provided mailboxIdentifier not found.
Vinokurov, et al. Expires 14 July 2024 [Page 23]
Internet-Draft Tigress January 2024
6.6. RelinquishMailbox
An application running on a remote device can invoke this API on
Relay Server to relinquish their ownership of the mailbox. Recipient
Device needs to present the currently established Recipient Device
Claim in order to relinquish their ownership of the mailbox. Once
relinquished, the mailbox can be bound to a different Recipient
Device that presents its Device Claim in a
ReadSecureContentFromMailbox call.
6.6.1. Endpoint
PATCH /{version}/m/{mailboxIdentifier}
6.6.2. Request Parameters
Path parameters:
* version (String, Required) - the version of the API. At the time
of writing this document, “v1”.
* mailboxIdentifier(String, Required) - MailboxIdentifier (refer to
Terminology).
Header parameters:
* Mailbox-Device-Claim (String, UUID, Required) - Device Claim
(refer to Terminology).
* Mailbox-Request-ID (String, UUID, Required) - Unique request
identifier.
6.6.3. Responses
200 Status: “200” (OK)
201 Status: “201” (Created) - response to a duplicate request
(duplicate "Mailbox-Request-ID"). Relay server SHALL respond to
duplicate requests with 201 without performing mailbox relinquish.
"Mailbox-Request-ID" passed in the first RelinquishMailbox request's
header SHALL be stored by the Relay server and compared to the same
value in the subsequent requests to identify duplicate requests. If
duplicate is found, Relay SHALL not perform mailbox relinquish, but
respond with 201 instead. The value of "Mailbox-Request-ID" of the
last successfully completed request SHALL be stored based on the
Device Claim passed by the caller.
Vinokurov, et al. Expires 14 July 2024 [Page 24]
Internet-Draft Tigress January 2024
401 Unauthorized - calling device is not authorized to relinquish a
mailbox. E.g. a device presented the incorrect Device Claim, or the
device is not bound to the mailbox.
404 Not Found - mailbox with provided mailboxIdentifier not found.
Relay server may respond with 404 if the Mailbox Identifier passed by
the caller is invalid.
7. Provisioning Information Structure
The Provisioning Information is the data transferred via the Relay
Server between the Initiator Device and Recipient Device. Each use
case defines its own specialized Provisioning Information format, but
all formats must at least adhere to the following structure. Formats
are free to define new top level keys, so clients shouldn't be
surprised if a message of an unexpected format has specialized top
level keys.
+=========+============+==========+==============================+
| Key | Type | Required | Description |
+=========+============+==========+==============================+
| format | String | Yes | The Provisioning Information |
| | | | format that the message |
| | | | follows. This is used by |
| | | | the Initiator Device and |
| | | | Recipient Device to know how |
| | | | to parse the message. |
+---------+------------+----------+------------------------------+
| content | Dictionary | Yes | A dictionary of content to |
| | | | be used for the credential |
| | | | transfer. See each format's |
| | | | specification for exact |
| | | | fields. |
+---------+------------+----------+------------------------------+
Table 1
7.1. Provisioning Information Format
Each Provisioning Information format must have the message structure
defined in an external specification.
Vinokurov, et al. Expires 14 July 2024 [Page 25]
Internet-Draft Tigress January 2024
+========================================+====================+==============+
|Format Type |Spec Link |Description |
+========================================+====================+==============+
|digitalwallet.carkey.ccc |[CCC-Digital-Key-30]|A digital |
| | |wallet |
| | |Provisioning |
| | |Information |
| | |for sharing a |
| | |car key that |
| | |follows the |
| | |Car |
| | |Connectivity |
| | |Consortium |
| | |specification.|
+----------------------------------------+--------------------+--------------+
|digitalwallet.generic.authorizationToken|[ISO-18013-5] |A digital |
| | |wallet |
| | |Provisioning |
| | |Information |
| | |for sharing a |
| | |generic pass |
| | |that relies |
| | |solely on an |
| | |authorization |
| | |token. |
+----------------------------------------+--------------------+--------------+
Table 2
{
"format" : "digitalwallet.carkey.ccc",
"content": {
// Format specific fields
}
}
Figure 8: Provisioning Information format
7.2. Provisioning Information Encryption
Provisioning Information will be stored on the Relay Server
encrypted. The Secret used to encrypt the Provisioning Information
should be given to the Recipient Device via a "Share URL" (a URL link
to a mailbox). The encrypted payload should be a data structure
having the following key-value pairs:
* "type" (String, Required) - the encryption algorithm and mode
used.
Vinokurov, et al. Expires 14 July 2024 [Page 26]
Internet-Draft Tigress January 2024
* "data" (String, Required) - Base64 encoded binary value of the
encrypted Provisioning Information, aka the ciphertext.
Please refer to [RFC5116] for the details of the encryption
algorithm.
The following algorithms and modes are mandatory to implement:
* "AEAD_AES_128_GCM": AES symmetric encryption algorithm with key
length 128 bits, in GCM mode with no padding. Initialization
Vector (IV) has the length of 96 bits randomly generated and tag
length of 128 bits.
* "AEAD_AES_256_GCM": AES symmetric encryption algorithm with key
length 256 bits, in GCM mode with no padding. Initialization
Vector (IV) has the length of 96 bits randomly generated and tag
length of 128 bits.
{
"type" : "AEAD_AES_128_GCM",
"data" : "IV ciphertext tag"
}
Figure 9: Secure Payload Format example
7.3. Share URL
A "Share URL" is the url a Initiator Device sends to the Recipient
Device allowing it to retrieve the Provisioning Information stored on
the Relay Server. A Share URL is made up of the following fields:
https://{RelayServerHost}/v{ApiVersion}/m/{MailboxIdentifier}?v={CredentialVertical}#{Secret}
Figure 10: Share URL example
Vinokurov, et al. Expires 14 July 2024 [Page 27]
Internet-Draft Tigress January 2024
+====================+====================+==========+
| Field | Location | Required |
+====================+====================+==========+
| RelayServerHost | URL Host | Yes |
+--------------------+--------------------+----------+
| ApiVersion | URI Path Parameter | Yes |
+--------------------+--------------------+----------+
| MailboxIdentifier | URI Path Parameter | Yes |
+--------------------+--------------------+----------+
| CredentialVertical | Query Parameter | No |
+--------------------+--------------------+----------+
| Secret | Fragment | No |
+--------------------+--------------------+----------+
Table 3
7.3.1. Credential Vertical in Share URL
When a user interacts with a share URL on a Recipient Device it can
be helpful to know what Credential Vertical this share is for. This
is particularly important if the Recipient Device has multiple
applications that can handle a share URL. For example, a Recipient
Device might want to handle a general access share in their wallet
app, but handle car key shares in a specific car application.
To properly route a share URL, the Initiator can include the
Credential Vertical in the share URL as a query parameter. The
Credential Vertical can't be included in the encrypted payload
because the Recipient Device might need to open the right application
before retrieving the secure payload. The Credential Vertical query
parameter uses the "v" key and supports the below types. If no
Credential Vertical is provided it will be assumed that this is a
general access share URL.
+================+=============+
| Vertical | Value |
+================+=============+
| General Access | a or _None_ |
+----------------+-------------+
| Home Key | h |
+----------------+-------------+
| Car Key | c |
+----------------+-------------+
Table 4
https://relayserver.example.com/v1/m/2bba630e-519b-11ec-bf63-0242ac130002?v=c#hXlr6aRC7KgJpOLTNZaLsw==
Vinokurov, et al. Expires 14 July 2024 [Page 28]
Internet-Draft Tigress January 2024
Figure 11: Car Key Share URL example
The Credential Vertical query parameter can be added to the share URL
by the Initiator Device when constructing the full share URL that is
going to be sent to the Recipient Device.
8. Security Considerations
8.1. Relay Server defined in this document
8.1.1. Confidentiality & Integrity
* Relay Server SHALL only allow TLS connections to thwart
eavesdropping or disruption of communication between Relay Server
and Initiator/Recipient.
* Relay Server SHALL use Device Claim to bind Initiator and exactly
one Recipient device to a mailbox. The binding prevents
eavesdropping or disruption of communication between Initiator and
Recipient via mailbox.
8.1.2. Network attacks
* An attacker may attempt to guess the MailboxIdentifier to
eavesdrop or disrupt communication. Using version 4 UUID
[RFC4122] for MailboxIdentifier SHOULD contain 122-bits of
cryptographic entropy. That makes brute-force guessing attacks
impractical. Also Relay Server generating MailboxIdentifiers
removes any chance of collision.
* It is possible to hosting malicious or untrusted scripts by relay
server preview page (ReadDisplayInformationFromMailbox). That can
be mitigated by not hosting a third party JavaScripts on a preview
page. Another approach is with a policy and tools to maintain the
trust of such scripts (e.g. force client to verify the script
against a good known hash of it).
* Relay server SHALL periodically check and delete expired mailboxes
( refer to expiration parameter in the CreateMailbox request).
This prevents un-authorized data leaks in future in addition to
general cleanup.
8.1.3. Privacy Considerations
* Relay Server SHALL not look into data exchanged over mailbox.
This is achieved by encrypting that data and making sure the
Secret doesn't land on Relay Server.
Vinokurov, et al. Expires 14 July 2024 [Page 29]
Internet-Draft Tigress January 2024
* At no time Relay server SHALL store or track the identities of
Initiator and Recipient. This is achieved by letting clients pick
Device Claims and Notification Tokens.
* Relay Server SHALL NOT be able to identify different mailboxes
that same device is interacting with. This is achieved by letting
clients pick Device Claims and Notification Tokens.
8.2. Clients of Relay Server
8.2.1. Confidentiality & Integrity
* Clients SHALL encrypt contents of the mailbox to protect it from
getting revealed to the Relay Server.
* Clients SHALL check cryptographic checksum of the content to
verify integrity of data. It's in the realm of Verticals to
define the details and out of scope of this document.
* It is recommended that URL and secret are send separately. But if
the Initiator sends both URL and the Secret as a single URL,
Secret MUST be appended as URI fragment [RFC3986]. Recipient
Device, upon receipt of such URL, MUST remove the Fragment
(Secret) before calling the Relay server API. This ensures that
Relay Server never ends up with the Secret to decode data.
“https://relayserver.example.com/v1/m/{mailboxIdentifier}#{Secret}”
Figure 12: Example of URL with Secret as URI Fragment
8.2.2. Privacy Considerations
* Notification Token SHALL NOT not contain identifying information.
It SHOULD also be different for every new share to prevent the
Relay server from correlating different shares.
* Notification token SHOULD only inform the corresponding device
that there is an update available on the corresponding mailbox.
Each device SHOULD keep track of all mailboxes associated with it
and make read calls to appropriate mailboxes.
* The value of Mailbox-Device-Attestation header parameter SHALL not
contain identifying information. It SHOULD also be different for
every new share to prevent the Relay server from correlating
different shares.
* Display Information is not encrypted, therefore, it SHOULD not
contain any identifying information.
Vinokurov, et al. Expires 14 July 2024 [Page 30]
Internet-Draft Tigress January 2024
8.3. Overall System
The overall system security considerations are in the realm of
Verticals. They are mentioned here for getting a better picture.
But these are not in scope of this document as Relay Server is a
piece of the overall System.
8.3.1. Initiator shares with the wrong Recipient
* Verticals allow Initiator to cancel in-flight shares and delete
completed shares.
8.3.2. Malicious Recipient forwards the share to 3rd party without
redeeming it or the Recipient's device is compromised.
* No mitigation, the Initiator SHOULD only share with receivers they
trust.
8.3.3. Invitation Channel Security
* For better user experience, the sharing flow SHOULD allow user
preferred channels. Users are familiar with these channels and
use them frequently for communication. Users typically consider
these channels as secure enough and trust them to deliver messages
to intended recipient. Some of these channels are end to end
encrypted and hence very secure and some are not. So depending on
channel used it's possible that the invitation is leaked to
determined attackers.
* Verticals can deploy various mitigations for this scenario.
- Verticals SHALL ensure that the Provisioning Information of a
share can only be redeemed exactly once. Relay Server helps in
this by guaranteeing that only one Recipient device gets the
Provisioning Information.
- Verticals can use second factor to authenticate the Recipient.
Verticals can use PIN codes, presence of Initiator Credential
or other mechanisms as second factor. The second factor
introduces friction to the smooth user experience during the
Provisioning process or at time of use of Credential. Details
of the second factor and policies around use of the second
factor are out of scope of this document.
Vinokurov, et al. Expires 14 July 2024 [Page 31]
Internet-Draft Tigress January 2024
9. IANA Considerations
This document registers new headers, "Mailbox-Request-ID", "Mailbox-
Device-Claim" and "Mailbox-Device-Attestation" in the "Permanent
Message Header Field Names" <https://www.iana.org/assignments/
message-headers>.
+----------------------------+----------+--------+---------------+
| Header Field Name | Protocol | Status | Reference |
+----------------------------+----------+--------+---------------+
| Mailbox-Request-ID | http | std | This document |
| Mailbox-Device-Claim | http | std | This document |
| Mailbox-Device-Attestation | http | std | This document |
+----------------------------+----------+--------+---------------+
Figure 13: Registered HTTP Header
10. References
10.1. Normative References
[CCC-Digital-Key-30]
Car Connectivity Consortium, "Digital Key Release 3", July
2022, <https://carconnectivity.org/download-digital-key-
3-specification/>.
[ISO-18013-5]
Cards and security devices for personal identification,
"Personal identification — ISO-compliant driving license —
Part 5: Mobile driving license (mDL) application",
September 2021, <https://www.iso.org/standard/69084.html>.
[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>.
[RFC3339] Klyne, G. and C. Newman, "Date and Time on the Internet:
Timestamps", RFC 3339, DOI 10.17487/RFC3339, July 2002,
<https://www.rfc-editor.org/rfc/rfc3339>.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, DOI 10.17487/RFC3986, January 2005,
<https://www.rfc-editor.org/rfc/rfc3986>.
Vinokurov, et al. Expires 14 July 2024 [Page 32]
Internet-Draft Tigress January 2024
[RFC4122] Leach, P., Mealling, M., and R. Salz, "A Universally
Unique IDentifier (UUID) URN Namespace", RFC 4122,
DOI 10.17487/RFC4122, July 2005,
<https://www.rfc-editor.org/rfc/rfc4122>.
[RFC5116] McGrew, D., "An Interface and Algorithms for Authenticated
Encryption", RFC 5116, DOI 10.17487/RFC5116, January 2008,
<https://www.rfc-editor.org/rfc/rfc5116>.
[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>.
10.2. Informative References
[RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818,
DOI 10.17487/RFC2818, May 2000,
<https://www.rfc-editor.org/rfc/rfc2818>.
Appendix A. Contributors
The following people provided substantive contributions to this
document:
* Casey Astiz
* Adam Bar-Niv
* Alexey Bulgakov
* Matt Byington
* Ben Chester
* Igor Gariev
* Manuel Gerster
* Jean-Luc Giraud
* Tommy Pauly
* Crystal Qin
Appendix B. Acknowledgments
TODO acknowledge.
Vinokurov, et al. Expires 14 July 2024 [Page 33]
Internet-Draft Tigress January 2024
Authors' Addresses
Dmitry Vinokurov
Apple Inc
Email: dvinokurov@apple.com
Yogesh Karandikar
Apple Inc
Email: ykarandikar@apple.com
Matthias Lerch
Apple Inc
Email: mlerch@apple.com
Alex Pelletier
Apple Inc
Email: a_pelletier@apple.com
Nick Sha
Alphabet Inc
Email: nicksha@google.com
Vinokurov, et al. Expires 14 July 2024 [Page 34]