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<!DOCTYPE html>
<html>
<head>
<title>Encrypted Data Vaults v0.1</title>
<meta http-equiv='Content-Type' content='text/html;charset=utf-8'/>
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// subtitle for the spec
subtitle: "A privacy-preserving, confidential storage and sharing mechanism",
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<body>
<section id='abstract'>
<p>
We store a significant amount of sensitive data online, such as personally
identifying information (PII), trade secrets, family pictures, and customer
information. The data that we store is often not protected in an appropriate
manner.
</p>
<p>
This specification describes a privacy-respecting mechanism for storing,
indexing, and retrieving encrypted data at a storage provider. It is often
useful when an individual or organization wants to protect data in a way that
the storage provider cannot view, analyze, aggregate, or resell the data.
This approach also ensures that application data is portable and protected
from storage provider data breaches.
</p>
</section>
<section id='sotd'>
<p>
This specification is a joint work item of the
<a href="https://www.w3.org/community/credentials/">W3C Credentials Community
Group</a> and the <a href="https://identity.foundation/">Decentralized
Identity Foundation</a>.
This specification is a combination of and iteration on work done by both of
these groups. Input documents, or parts thereof, which have not yet been
integrated into the specification may be found in the appendices.
</p>
</section>
<section class="informative">
<h2>
Introduction
</h2>
<p>
We store a significant amount of sensitive data online, such as personally
identifying information (PII), trade secrets, family pictures, and customer
information. The data that we store is often not protected in an appropriate
manner.
</p>
<p>
Legislation, such as the General Data Protection Regulation (GDPR), incentivizes
service providers to better preserve individuals' privacy, primarily through
making the providers liable in the event of a data breach. This liability
pressure has revealed a technological gap, whereby providers are often not
equipped with technology that can suitably protect their customers. Encrypted
Data Vaults fill this gap and provide a variety of other benefits.
</p>
<p>
This specification describes a privacy-respecting mechanism for storing,
indexing, and retrieving encrypted data at a storage provider. It is often
useful when an individual or organization wants to protect data in a way that
the storage provider cannot view, analyze, aggregate, or resell the data.
This approach also ensures that application data is portable and protected
from storage provider data breaches.
</p>
<section class="informative">
<h3>
Why Do We Need Confidential Storage?
</h3>
<p class="issue">
Explain why individuals and organizations that want to protect their privacy,
trade secrets, and ensure data portability will benefit from using this
technology. Explain how giving a standard API for the storage of user data
empowering users to "bring their own storage", giving them control of their
own information. Explain how applications that are written against a standard
API and assume that users will bring their own storage can separate concerns
and focus on the functionality of their application, removing the need to
deal with storage infrastructure (instead leaving it to a specialist service
provider that is chosen by the user).
</p>
<p>
Requiring client-side (edge) encryption for all data and metadata at the same
time as enabling the user to store data on multiple devices and to share data
with others, whilst also having searchable or queryable data, has been
historically very difficult to implement in one system. Trade-offs are often
made which sacrifice privacy in favor of usability, or vice versa.
</p>
<p>
Due to a number of maturing technologies and standards, we are hopeful that such
trade-offs are no longer necessary, and that it is possible to design a
privacy-preserving protocol for encrypted decentralized data storage that has
broad practical appeal.
</p>
</section>
<section class="informative">
<h3>
Ecosystem Overview
</h3>
<p>
The problem of decentralized data storage has been approached from various
different angles, and personal data stores (PDS), decentralized or otherwise,
have a long history in commercial and academic settings. Different approaches
have resulted in variations in terminology and architectures.
The diagram below shows the types of components that are emerging, and the roles
they play. Encrypted Data Vaults fulfill the low-level encrypted
<em>storage</em> role.
</p>
<figure>
<img style="margin: auto; display: block; width: 75%;"
src="diagrams/SDS_Layers.svg" alt="diagram showing
the roles of different technologies in the encrypted
data vaults and secure data store ecosystem and how they interact.">
<figcaption style="text-align: center;">
Confidential Storage layers
</figcaption>
</figure>
<p>
This section describes the roles of the core actors and the relationships
between them in an ecosystem where this specification is expected
to be useful. A role is an abstraction that might be implemented in many
different ways. The separation of roles suggests likely interfaces and
protocols for standardization. The following roles are introduced in this
specification:
</p>
<dl>
<dt><dfn>data vault controller</dfn></dt>
<dd>
A role an <a>entity</a> might perform by creating, managing, and deleting
data vaults. This entity is also responsible for granting and revoking
authorization to <a>storage agents</a> to the data vaults that are under its
control.
</dd>
<dt><dfn data-lt="storage agents">storage agent</dfn></dt>
<dd>
A role an <a>entity</a> might perform by creating, updating, and deleting
data in a data vault. This entity is typically granted authorization to
to access a data vault by a <a>data vault controller</a>.
</dd>
<dt><dfn>storage provider</dfn></dt>
<dd>
A role an <a>entity</a> might perform by providing a raw data storage
mechanism to a <a>data vault controller</a>. It is impossible for this entity
to see the data that it is storing due to all data being encrypted at rest
and in transit to and from the <a>storage provider</a>.
</dd>
</dl>
</section>
<section class="informative">
<h3>
Requirements
</h3>
<p>
The following sections elaborate on the requirements that have been gathered
from the core use cases.
</p>
<section>
<h4>
Privacy and multi-party encryption
</h4>
<p>
One of the main goals of this system is ensuring the privacy of an entity's
data so that it cannot be accessed by unauthorized parties, including the
storage provider.
</p>
<p>
To accomplish this, the data must be encrypted both while it is in transit
(being sent over a network) and while it is at rest (on a storage system).
</p>
<p>
Since data could be shared with more than one entity, it is also necessary for
the encryption mechanism to support encrypting data to multiple parties.
</p>
</section>
<section>
<h4>
Sharing and authorization
</h4>
<p>
It is necessary to have a mechanism that enables authorized sharing
of encrypted information among one or more entities.
</p>
<p>
The system is expected to specify one mandatory authorization scheme,
but also allow other alternate authorization schemes. Examples of
authorization schemes include OAuth2 and
[[ZCAP]]s (Authorization Capabilities).
</p>
</section>
<section>
<h4>
Identifiers
</h4>
<p>
The system should be identifier agnostic. In general, identifiers that are a
form of URN or URL are preferred. While it is presumed that [[DID-CORE]]
(Decentralized Identifiers, DIDs) will be used by the system in a few important ways, hard-coding the implementations to DIDs would be an anti-pattern.
</p>
</section>
<section>
<h4>
Versioning and replication
</h4>
<p>
It is expected that information can be backed up on a continuous basis. For this
reason, it is necessary for the system to support at least one mandatory
versioning strategy and one mandatory replication strategy, but also allow other
alternate versioning and replication strategies.
</p>
</section>
<section>
<h4>
Metadata and searching
</h4>
<p>
Large volumes of data are expected to be stored using this system, which then
need to be efficiently and selectively retrieved. To that end, an encrypted
search mechanism is a necessary feature of the system.
</p>
<p>
It is important for clients to be able to associate metadata with the data such
that it can be searched. At the same time, since privacy of both data <em>and</em>
metadata is a key requirement, the metadata must be stored in an encrypted
state, and service providers must be able to perform those searches in an opaque
and privacy-preserving way, without being able to see the metadata.
</p>
</section>
<section>
<h4>
Protocols
</h4>
<p>
Since this system can reside in a variety of operating environments, it is
important that at least one protocol is mandatory, but that other protocols are
also allowed by the design. Examples of protocols include HTTP, gRPC, Bluetooth,
and various binary on-the-wire protocols. An HTTPS API is defined in <a href="#data-vault-https-api"></a>.
</p>
</section>
</section>
<section class="informative">
<h3>
Design goals
</h3>
<p>
This section elaborates upon a number of guiding principles and design goals
that shape Encrypted Data Vaults.
</p>
<section>
<h4>
Layered and modular architecture
</h4>
<p>
A layered architectural approach is used to ensure that the foundation for the
system is easy to implement while allowing more complex functionality to be
layered on top of the lower foundations.
</p>
<p>
For example, Layer 1 might contain the mandatory features for the most basic
system, Layer 2 might contain useful features for most deployments, Layer 3
might contain advanced features needed by a small subset of the ecosystem, and
Layer 4 might contain extremely complex features that are needed by a very small
subset of the ecosystem.
</p>
</section>
<section>
<h4>
Prioritize privacy
</h4>
<p>
This system is intended to protect an entity's privacy. When exploring new
features, always ask "How would this impact privacy?". New features that
negatively impact privacy are expected to undergo extreme scrutiny to determine
if the trade-offs are worth the new functionality.
</p>
</section>
<section>
<h4>
Push implementation complexity to the client
</h4>
<p>
Servers in this system are expected to provide functionality strongly focused on
the storage and retrieval of encrypted data. The more a server knows, the
greater the risk to the privacy of the entity storing the data, and the more
liability the service provider might have for hosting data. In addition, pushing
complexity to the client enables service providers to provide stable server-side
implementations while innovation can by carried out by clients.
</p>
</section>
</section>
<section id="conformance" class="normative">
</section>
</section>
<section class="informative">
<h2>
Terminology
</h2>
<div data-include="./terms.html"
data-oninclude="restrictReferences">
</div>
</section>
<section class="informative">
<h2>
Core Concepts
</h2>
<p>
The following sections outline core concepts, such as encrypted storage,
which form the foundation of this specification.
</p>
<section class="normative">
<h2>
Encrypted Storage
</h2>
<p>
An important consideration of encrypted data stores is which components of the
architecture have access to the (unencrypted) data, or who controls the private
keys. There are roughly three approaches: storage-side encryption, client-side
(edge) encryption, and gateway-side encryption (which is a hybrid of the
previous two).
</p>
<p>
Any data storage systems that let the user store arbitrary data also support
client-side encryption at the most basic level. That is, they let the user
encrypt data themselves, and then store it. This doesn't mean these systems are
optimized for encrypted data however. Querying and access control for encrypted
data may be difficult.
</p>
<p>
Storage-side encryption is usually implemented as whole-
<a href="https://en.wikipedia.org/wiki/Disk_encryption">disk encryption</a>
or filesystem-level encryption. This is widely supported and understood, and any
type of hosted cloud storage is likely to use storage-side encryption. In this
scenario the private keys are managed by the service provider or controller of
the storage server, which may be a different entity than the user who is storing
the data. Encrypting the data while it resides on disk is a useful security
measure should physical access to the storage hardware be compromised, but does
not guarantee that <em>only</em> the original user who stored the data has access.
</p>
<p>
Conversely, client-side encryption offers a high level of
security and privacy, especially if metadata can be encrypted as well. Encryption
is done at the individual data object level, usually aided by a keychain or wallet
client, so the user has direct access to the private keys. This comes at a cost,
however, since the significant responsibility of key management and recovery falls
squarely onto the end user. In addition, the question of key management becomes
more complex when data needs to be shared.
</p>
<p>
Gateway-side encryption systems take an approach that combines
techniques from storage-side and client-side encryption architectures. These
storage systems, typically encountered among multi-server clusters or some
"encryption as a platform" cloud service providers, recognize that client-side
key management may be too difficult for some users and use cases, and offer to
perform encryption and decryption themselves in a way that is transparent to
the client application. At the same time, they aim to minimize the number of
components (storage servers) that have access to the private decryption keys.
As a result, the keys usually reside on "gateway" servers, which encrypt the
data before passing it to the storage servers. The encryption/decryption is
transparent to the client, and the data is opaque to the storage servers, which
can be modular/pluggable as a result. Gateway-side encryption provides some
benefits over storage-side systems, but also share the drawbacks: the gateway
sysadmin controls the keys, not the user.
</p>
</section>
<section class="normative">
<h2>
Encrypted Resources
</h2>
<section class="normative">
<h3>
Structured Document Resources
</h3>
<p>
The fundamental unit of storage in data vaults is the encrypted
structured document which, when decrypted, provides a data structure that
can be expressed in popular syntaxes such as JSON and CBOR. Documents can
store structured data and metadata about the structured data.
</p>
</section>
<section class="normative">
<h3>
Stream Resources
</h3>
<p>
For documents larger than 10MiB or for raw binary data formats such as audio,
video, and office productivity files, a streaming API is provided that
enables data to be streamed to/from a data vault. Streams are described using
structured documents, but the storage of the data is separated from the
structured document using a hashlink to the encrypted content.
</p>
</section>
</section>
<section class="normative">
<h2>
Indexing and Querying
</h2>
<p>
Data vaults are expected to store a very large number of documents
of varying kinds. This means that it is important to be able to search the
documents in a timely way, which creates a challenge for the storage provider
as the content is encrypted. An encrypted querying scheme is provided for
secure data vaults that enable data vault clients to do metadata indexing while
<em>not leaking</em> metadata to the storage provider.
</p>
</section>
<section class="normative">
<h2>
Operations
</h2>
<p>
Data vaults allow for the classic set of CRUD (Create, Read, Update and Delete)
operations on its data models.
</p>
<section class="normative">
<h3>
Create Operation
</h3>
<ul>
<li>
Create Vault: Creates/provisions an Encrypted Data Vault by specifying a
<code>DataVaultConfiguration</code> structure. This includes Replication configuration.
</li>
<li>
Create Index: Creates an Index for a particular Vault.
</li>
<li>
Create Resource (Document or Stream): Creates a Resource in a given Vault.
</li>
</ul>
</section>
<section class="normative">
<h3>
Read Operation
</h3>
<ul>
<li>
Read Vault Configuration: Returns the <code>DataVaultConfiguration</code> object
for a given Vault.
</li>
<li>
Read Index: Returns the Index configuration object.
</li>
<li>
Read Resource (Document or Stream): Returns the given resource.
</li>
</ul>
</section>
<section class="normative">
<h3>
Update Operation
</h3>
<p class="issue">
Does an Update Index operation make sense?
</p>
<ul>
<li>
Update Vault Configuration: Modifies the <code>DataVaultConfiguration</code>
object for a given Vault.
</li>
<li>
Update Index: Modifies the Index configuration object.
</li>
<li>
Update Resource (Document or Stream): Updates the encrypted resource (note that
this is a "full replace" operation).
</li>
</ul>
</section>
<section class="normative">
<h3>
Delete Operation
</h3>
<p class="issue" data-number="114"></p>
<ul>
<li>
Delete Vault Configuration: Deletes a Vault.
</li>
<li>
Delete Index: Deletes an Index.
</li>
<li>
Delete Resource (Document or Stream): Deletes the encrypted resource (note that
a tombstone object should remain behind for replication purposes).
</li>
</ul>
</section>
<section class="normative">
<h3>
Query Operation
</h3>
<ul>
<li>
Send Encrypted Index Query: Queries the encrypted resources in a given data vault based on created
indexes.
</li>
</ul>
</section>
</section>
<section class="normative">
<h2>
Authorization Structure
</h2>
<p class="issue" data-number="134"></p>
</section>
<section class="normative">
<h2>
Authorization Invocation
</h2>
<p class="issue" data-number="135"></p>
</section>
</section> <!--end Core Concepts-->
<section class="normative">
<h2>
Architecture
</h2>
<p class="issue">
Review this section for language that should be properly normative.
</p>
<p>
This section describes the architecture of the Encrypted Data Vault protocol, in
the form of a client-server relationship. The vault is regarded as the server and
the client acts as the interface used to interact with the vault.
</p>
<p>
This architecture is layered in nature, where the foundational layer consists of
an operational system with minimal features, and where more advanced features are
layered on top. Implementations can choose to implement only the foundational
layer, or optionally, additional layers consisting of a richer set of features
for more advanced use cases.
</p>
<section>
<h3>
Server and client responsibilities
</h3>
<p>
The server is assumed to be of low trust, and must have no visibility into the
data that it persists. However, even in this model, the server still has a set
of minimum responsibilities it must adhere to.
</p>
<p>
The client is responsible for providing an interface to the server, with
bindings for each relevant protocol (HTTP, RPC, or binary over-the-wire
protocols), as required by the implementation.
</p>
<p>
All encryption and decryption of data is done on the client side, at the edges.
The data (including metadata) MUST be opaque to the server, and the architecture
is designed to prevent the server from being able to decrypt it.
</p>
</section>
<section>
<h3>
Layer 1 (L1) responsibilities
</h3>
<p>
Layer 1 consists of a client-server system that is capable of encrypting data in
transit and at rest.
</p>
<section>
<h4>
Server: validate requests (L1)
</h4>
<p>
When a vault client makes a request to store, query, modify, or delete data in
the vault, the server validates the request. Since the actual data and metadata
in any given request is encrypted, such validation is necessarily limited and
largely depends on the protocol and the semantics of the request.
</p>
</section>
<section>
<h4>
Server: Persist data (L1)
</h4>
<p>
The mechanism a server uses to persist data, such as storage on a local,
networked, or distributed file system, is determined by the implementation. The
persistence mechanism is expected to adhere to the common expectations of a data
storage provider, such as reliable storage and retrieval of data.
</p>
</section>
<section>
<h4>
Server: Persist global configuration (L1)
</h4>
<p>
A vault has a global configuration that defines the following properties:
</p>
<ul>
<li>
Stream chunk size
</li>
<li>
Other config metadata
</li>
</ul>
<p>
The configuration allows the the client to perform capability discovery
regarding things like authorization, protocol, and replication mechanisms that are used
by the server.
</p>
</section>
<section>
<h4>
Server: enforcement of authorization policies (L1)
</h4>
<p>
When a client makes a request to store, query, modify, or delete data in
the vault, the server enforces any authorization policy that is associated with
the request.
</p>
</section>
<section>
<h4>
Client: encrypted data chunking (L1)
</h4>
<p>
An Encrypted Data Vault is capable of storing many different types of data,
including large unstructured binary data. This means that storing a file as a
single entry would be challenging for systems that have limits on single record
sizes. For example, some databases set the maximum size for a single record to
16MB. As a result, it is necessary that large data is chunked into sizes that
are easily managed by a server. It is the responsibility of the client to set
the chunk size of each resource and chunk large data into manageable chunks for
the server. It is the responsibility of the server to deny requests to store
chunks larger than 1MiB, which is the maximum size for a single chunk.
</p>
<p>
Each chunk is encrypted individually using authenticated encryption. Doing so
protects against attacks where an attacking server replaces chunks in a large
file and requires the entire file to be downloaded and decrypted by the victim
before determining that the file is compromised. Encrypting each chunk with
authenticated encryption ensures that a client knows that it has a valid chunk
before proceeding to the next one. Note that another authorized client can still
perform an attack by doing authenticated encryption on a chunk, but a server is
not capable of launching the same attack.
</p>
</section>
<section>
<h4>
Client: Resource structure (L1)
</h4>
<p>
The process of storing encrypted data starts with the creation of a Resource by
the client, with the following structure.
</p>
<p>
Resource:
</p>
<ul>
<li>
<code>id</code> (required)
</li>
<li>
<code>meta</code>
<ul>
<li>
<code>meta.contentType</code> MIME type
</li>
</ul>
</li>
<li>
<code>content</code> - entire payload, or a manifest-like list of hashlinks to individual chunks
</li>
</ul>
<p>
If the data is less than the chunk size, it is embedded directly into the
<code>content</code>.
</p>
<p>
Otherwise, the data is sharded into chunks by the client (see next section), and
each chunk is encrypted and sent to the server. In this case, <code>content</code>
contains a manifest-like listing of URIs to individual chunks (integrity-protected
by [[HASHLINK]].
</p>
</section>
<section>
<h4>
Client: Encrypted resource structure (L1)
</h4>
<p>
The process of creating the Encrypted Resource. If the data was sharded into
chunks, this is done after the individual chunks are written to the server.
</p>
<ul>
<li>
<code>id</code>
</li>
<li>
<code>index</code> - encrypted index tags prepared by the client (for use with
privacy-preserving querying over encrypted resources)
</li>
<li>
<em>Chunk size</em> (if different from the default in global config)
</li>
<li>
<em>Versioning metadata</em> - such as sequence numbers, Git-like hashes, or other mechanisms
</li>
<li>
<em>Encrypted resource payload</em> - encoded as a <code>jwe</code> [[RFC7516]]
</li>
</ul>
</section>
</section>
<section>
<h3>
Layer 2 (L2) responsibilities
</h3>
<p>
Layer 2 consists of a system that is capable of sharing data among multiple
entities, of versioning and replication, and of performing privacy-preserving searches
in an efficient manner.
</p>
<section>
<h4>
Client: Encrypted search indexes (L2)
</h4>
<p>
To enable privacy-preserving querying (where the search index is opaque to the
server), the client must prepare a list of encrypted index tags (which are stored
in the Encrypted Resource, alongside the encrypted data contents).
</p>
<p class="issue">
Need details about salting and encryption mechanism of index tags.
</p>
</section>
<section>
<h4>
Client: Versioning and replication (L2)
</h4>
<p>
A server must support <em>at least one</em> versioning/change control mechanism.
Replication is done by the client, not by the server (since the client controls
the keys, knows about which other servers to replicate to, etc.). If an
Encrypted Data Vault implementation aims to provide replication functionality,
it MUST also pick a versioning/change control strategy (since replication
necessarily involves conflict resolution). Some versioning strategies are
implicit ("last write wins", eg. <code>rsync</code> or uploading a file to a file
hosting service), but keep in mind that a replication strategy <em>always</em> implies
that some sort of conflict resolution mechanism should be involved.
</p>
</section>
<section>
<h4>
Client: Sharing with other entities
</h4>
<p>
An individual vault's choice of authorization mechanism determines how a client
shares resources with other entities (authorization capability link or similar
mechanism).
</p>
</section>
</section>
<section>
<h3>
Layer 3 (L3) responsibilities
</h3>
<section>
<h4>
Server: Notifications (L3)
</h4>
<p>
It is helpful if data storage providers are able to notify clients when changes
to persisted data occurs. A server may optionally implement a mechanism by which
clients can subscribe to changes in the vault.
</p>
</section>
<section>
<h4>
Client: Vault-wide integrity protection (L3)
</h4>
<p>
Vault-wide integrity protection is provided to prevent a variety of storage
provider attacks where data is modified in a way that is undetectable, such as
if documents are reverted to older versions or deleted. This protection
requires that a global catalog of all the resource identifiers that belong to a
user, along with the most recent version, is stored and kept up to date by the
client. Some clients may store a copy of this catalog locally (and
include integrity protection mechanism such as [[HASHLINK]] to guard against
interference or deletion by the server.
</p>
</section>
</section>
</section>
<section class="normative">
<h2>
Data Model
</h2>
<p>
The following sections outlines the data model for data vaults.
</p>
<section>
<h3>
DataVaultConfiguration
</h3>
<p class="issue">
Data vault configuration isn't strictly necessary for using the other features
of data vaults. This should have its own conformance section/class or potentially
event be non-normative.
</p>
<p>
A data vault configuration specifies the properties a particular data vault
will have.
</p>
<table class="simple">
<thead>
<th style="white-space: nowrap">Property</th>
<th>Description</th>
</thead>
<tbody>
<tr>
<td>sequence</td>
<td>
A unique counter for the data vault in order to ensure that
clients are properly synchronized to the data vault. The value is required and
MUST be an unsigned 64-bit number.
</td>
</tr>
<tr>
<td>controller</td>
<td>
The entity or cryptographic key that is in control of the
data vault. The value is required and MUST be a URI.
</td>
</tr>
<tr>
<td>invoker</td>
<td>
The root entities or cryptographic key(s) that are authorized to invoke
an authorization capability to modify the data vault's configuration or
read or write to it. The value is optional, but if present, MUST be a URI
or an array of URIs. When this value is not present, the value of controller
property is used for the same purpose.
</td>
</tr>