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Transfer dIGital cREdentialS Securely

Document Charter Transfer dIGital cREdentialS Securely WG (tigress)
Title Transfer dIGital cREdentialS Securely
Last updated 2022-07-19
State Approved
WG State Active
IESG Responsible AD Roman Danyliw
Charter edit AD Roman Danyliw
Send notices to (None)

There are many situations in which it is desirable to transfer a copy of a
digital credential to another person. For example, a private car owner may want
to provide access to their vehicle to a friend or a family member. A private
homeowner may want to provide access to their home to their cat sitter. An
individual staying at a hotel may want to transfer a copy of a hotel room key
to their spouse. Today, no such standardized method exists in a cross-platform,
credential type-agnostic capacity.

The WG will standardize a protocol that will facilitate such credential
transfers from one person's device to another person's device. The
protocol will leverage a "relay server" to transfer data from sender
to recipient. The scope of the transfer is limited to a single origin device
and a single destination device. Note: neither private keys nor secret
symmetric keys present on the sender's device are exchanged during the
transfer operation. In the transfer protocol, the “credential” is the
information issued by a credential authority for a given user and device that
allows them to have access rights to a certain asset.  The “share” is a data
structure transferred from the sender to recipient that comprises the data both
necessary and sufficient for the recipient to request a new credential from the
credential authority to provision it to the receiving device.

Privacy goals include:

* 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

Sufficient security measures should be embedded in the protocol in an effort to:

* 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)

The solution the WG defines is expected to:

* 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

The following topics are out of scope for the WG:

* Defining the mechanism the receiver will use in order to provision the
credential with the credential authority

* The User Interface (UI) that is displayed to the sender or receiver during
sending or receiving (this will depend on the device manufacturer's
interface guidelines)

* Defining the format or content of each field within the encrypted data (i.e.,
the provisioned credentials and associated information) stored on the relay

The WG will deliver a protocol to facilitate secure credential transfer. The WG
must consider all Privacy and Security goals in an effort to perform the
credential transfer securely. The protocol will use appropriate cryptographic
mechanisms to protect the transferred credentials in accordance with the
security and privacy goals described above.