No on Universal Patient ID


Last week the House slipped a provision into the budget bill that would lift the funding ban on exploring a universal patient identifier. The ban is known as the Foster-Kelly amendment. If approved by the Senate, exploration of a universal patient identifier (UPI) could begin in earnest.

I strongly oppose the UPI or universal identifiers of any sort. While healthcare IT professionals may wish for a single identifier to make correlating information easier, I don't know many identity professionals who would advocate universal identifiers.

We have other examples of universal identifiers like Social Security Numbers and even cell phone numbers. Your email address is another universal identifier. The problem with universal identifiers is twofold: First, they are indiscriminate; they don't care who's using them to correlate information about a person. The bad guys, scammers, and surveillers can use them just as easily as the doctors and hospitals. Second, computers make correlating information based on a universal identifier far too easy.

As a result, universal identifiers are a threat to privacy and personal security. No matter what safeguards you put in place, creating a universal identifier scheme like a UPI is going to cause harm to people. Universal identifiers are a 20th Century solution that has no business being used in the 21st Century.

The good news is there's usually no need to create universal identifiers. Use cases for a UPI can be supported without a universal identifier thanks to advances in cryptography and its application. Self-sovereign identity (SSI) provides a model for how to put people at the center of their healthcare and allow them to correlate data where desirable without exposing their records to unwanted correlation by third parties. Hyperledger Indy and Aries are open source projects that support SSI. Sovrin is a project that makes it real and usable.

Ironically, just as we are able to create interoperability and provide patient safety without using a UPI, it's finally moving forward. Instead of creating new privacy and security problems for Americans, I implore the US Senate to earmark funds for exploring how to use SSI to solve the healthcare records problem.

Photo Credit: Patient from PxHere (CC0)

Thoughts on Libra


Yesterday, after months of speculation, Facebook announced Libra, a cryptocurrency with the mission of enabling a simple global currency and financial infrastructure that empowers billions of people.

That's a worthy goal. But, as you'd expect with almost anything Facebook does these days, there was a lot of reaction ranging from skepticism to outright opposition.

As Chair of the Sovrin Foundation, I've had a lot of people ask my opinion on Libra.


One thing that I like about Libra is that it's not just a Facebook coin, which is what I had imagined when I first heard about it. Rather, Libra is a Swiss-based organization and Facebook is just one of (eventually) 100 members. Voting in Libra is stake-based, so that doesn't necessarily mean Facebook will just have 1% of the voting power. They could have much more depending on their stake.

An independent, multilateral governing organization is a good design choice. I have no evidence that Sovrin Foundation served as a model in any way, but that choice is aligned with the governance model we've pioneered with the Sovrin Governance Framework.

That said, there's a big difference in the governing model of Libra and Sovrin. Libra is very clearly an industry association. The governance is controlled by the organizations who stake it and these organizations will be making decisions about how Libra operates based on what's good for them. Sovrin Foundation, on the other hand, is NOT an industry association because we want Sovrin to support Identity for All, rather than identity in the service of a few large companies.


Facebook will play a big role in the success of Libra. With 1.7 billion users, they can incorporate Libra into their apps and make it useful for payments on Facebook, Instagram, WhatsApp, and beyond. They won't need exchanges—they are their own exchange. Libra can become useful for lots of people very quickly as a medium of exchange inside Facebook's ecosystem. That ignores a lot of other use cases outside of Facebook, but clearly this is a Facebook play and their user base is a large reason others have joined in.

That kind of reach will be huge for cryptocurrencies in general because it will get people used to the idea of using crypto. When lots of people have Libra coins, other utility tokens will be incentivized to build in support for exchanging Libra for their tokens. Libra could become a common currency for various projects.

And we can't ignore the validation this gives to the idea of tokens in general. As Erik Voorhees said on Twitter: "Zoom out for a second and realize how far this industry has come. The biggest companies in the world are now launching cryptocurrencies. BOOM." Crypto is now mainstream.


The Libra Whitepaper includes this paragraph:

An additional goal of the association is to develop and promote an open identity standard. We believe that decentralized and portable digital identity is a prerequisite to financial inclusion and competition.

That's all it says, so it's hard to know what exactly it means. The first question in my mind is what do they mean when they say "identity"? Are they thinking in traditional digital identity terms where identity is mostly about authentication and maybe KYC around a small set of attributes? They give no clues that they are considering anything beyond that. I hope they're not thinking of tying Libra addresses to some correlatable identifier since that will be a privacy nightmare.

Second, there's already a number of open identity standards. They don't say why they think they need to develop another one. Of course, the common mindset among most corporate types is that identity is a silo that you build yourself, so it may be nothing more considered than the default view.

Third, portable, digital identity exists now in Sovrin. There's no reason, of course, that Sovrin's identity metasystem can't serve as the basis for identity in Libra. And there are many reasons why it should. Sovrin provides a flexible, open, and public metasystem that can easily serve as the foundation for the identity services a system like Libra would need to support financial inclusion without surveillance. Financial inclusion shouldn't come at the cost of privacy.


Of course, this is just the announcement. The launch isn't for another year and lots will change as Libra moves from the drawing board to reality.

Overall, I see Libra as a good development. One that will push the crypto space forward and drive adoption. Rather than destroying other cryptocurrencies and tokens, Libra augments them and validates them. Every coin or token has to live or die on the basis of its utility and Libra doesn't change that. The world needs multiple tokens because they represent the means of exchange in a particular network and provide market incentives in the context of that network. Libra is a big step toward a world where market-driven networks are the norm. That's a good thing.

Photo Credit: Libra Digital from Public Domain Pictures (CC0)

DID Messaging: A Batphone for Everyone


In my last post, I wrote about a demo given by BCGov, Spark NZ, and Streetcred ID at the last Internet Identity Workshop. That demo caused a lot of people to download and try out Streetcred ID's digital wallet. One of the features that Streetcred ID built into their wallet was peer-to-peer messaging based on DID Messaging and that led to some interesting insights.

A Brief Primer on DIDs

If you're not familiar with DIDs, take a minute to go read my article on Decentralized Identifiers from earlier this year. I'll summarize the relevant parts here:

  • DIDs are a new type of cryptographic identifier that are resolvable, non-reassignable, and decentralized (not under the control of a single authority).
  • DIDs have at least one associated public/private key pair.
  • The public key(s) and endpoints associated with a DID can be retrieved by resolving the DID and getting them from the resulting DID Document.

DIDs are inexpensive to create, so best practice is to create a new DID for every one with whom you create a digital relationship. The exchange of these so-called "peer DIDs" thus creates a mutually-authenticated relationship between the participants, where each can use the public key associated with the other's DID to authenticate them.

The wide use of peer DID exchange creates a network of peer-to-peer relationships that are not only mutually authenticated, but can exchange encrypted messages with each other. This capability requires the use of a DID Messaging protocol like the one found in the open-source Hyperledger Aries codebase1 that forms the basis for peer-to-peer interactions in the Sovrin network. The software that exchanges these messages for each party is called an "agent".

DID Messaging

As I mentioned, the Streetcred ID digital wallet supports peer-to-peer messaging through Sovrin P2P agents. This is something any wallet based on Aries and Sovrin could do, but as far as I know, Streetcred ID's wallet is the first to explore this capability.

After IIW, a friend of mine, Tim Bouma, was talking about the P2P messaging in the Streetcred wallet. He hadn't been at IIW, but I opened my wallet and created an invitation for Tim and sent it to him in a Twitter DM.

Creating a DID Invitation
Creating a DID Invitation in Streetcred ID's Digital Wallet (click to enlarge)

Tim accepted the invitation, but how could I be sure it was him--that Malory hadn't intercepted the invitation I sent Tim and inserted himself in the middle of the communication? Fortunately the wallet had a solution. I was able to ask Tim to prove things about himself based on credentials he had in his wallet.

Verifying the Relationship
Verifying the Relationship using an Email Credential (click to enlarge)

Once Tim has proven his email address to me from a credential, I was more sure I was really connected to Tim. For a higher value exchange, I could have asked for other information from Tim until I was sure that it was really him on the other end. With that, we were able to exchange messages. The software took care of encrypting our communication and ensuring that my discussion with Tim was both protected and to him alone.

Messaging in the Streetcred ID digital wallet
Messaging in the Streetcred ID Digital Wallet (click to enlarge)

The Batphone

After this exchange, Vic Cooper likened DID-based P2P messaging to the Batphone. When Batman picks up the Batphone to talk with Commissioner Gordon, Commissioner Gordon doesn't start off the conversation with "Who am I speaking to?", "Can you give me your account number?", "What's your date of birth?", or "What street did you live on in Junior High?" When Commissioner Gordon picks up the Batphone, he knows it's Batman on the other end. Only Batman can call on the Batphone.

So DID Messaging is like having a Batphone for every digital relationship you have. You and they know they're communicating with the right party2. All the messages are protected from eavesdroppers.

DID Messaging could revolutionize how we talk to each other and how we communicate with businesses.

  • We no longer have to rely on a correlatable identifier like an email or phone number, to identify the other party.
  • We no longer have to use centralized systems to talk to other parties with the attendant risk of the system being down or the conversation not being private.
  • We save time and money using frictionless communications with companies we need to work with. We might even get better service.
  • We can verify who's at the other end by asking them to prove things to us.
  • We can sever one relationship without affecting others since everyone has a different identifier for us.

DID Messaging is the foundation for verifiable credential exchange, but is more general purpose and can be used to reliably and securely exchange messages with anyone else who has a digital wallet that supports DIDs3.


  1. The Aries project was recently split off from the Hyperledger Indy project.
  2. If you're concerned about losing your phone and having all those relationships exposed, see What If I Lose My Phone.
  3. Not all digital wallets currently expose the DID messaging functionality, but any that do will be compatible with each other.

Self-Sovereign Identity at IIW: We Have Liftoff

Liftoff of the SpaceX Falcon 9 rocket carrying NASA's TESS spacecraft.

Last week was the 28th semi-annual Internet Identity Workshop (IIW). There were 129 session conducted by people from all over the world and about many different aspects of identity. There were technical discussions, standards works, policy debates, and lots of demonstrations. I'll post a link to the Book of Proceedings when it's available so you can read about them yourself.1

One thing that stood out to me is the impact self-sovereign identity is having. There were several dozen sessions on SSI. I was excited to see seven different implementations of Indy Agents that were working together and combined to create several demonstrations of credential exchange.

  • Evernym and Onfido did a demonstration of the wallet and the Onfido identity verification service. You can do it too. Download the app to you phone and then in the "Menu" select the Onfido item and start getting a real, live, production identity verification based on an existing identity credential such as a passport or drivers license. Once you do, you'll have a connection to and credential from Onfido.

    You can also go to and walk through a demonstration of how credential exchange can work, using actual (though not real) credentials in your wallet

  • Vonx (BC Gov), StreetCred, and Spark NZ showed a demonstration using a StreetCred wallet to connect to and get credentials from two different services: a Vonx email verification service and an IIW attendee verification service. Once attendees had both of those credentials, they could use them to unlock a box that Spark had built and brought to the workshop.

  • IDRamp showed a demonstration of their product that can add credentials to any system that speaks SAML. They were demonstrating using a wallet to present a credential to log into Slack and Rocketchat. This is a production service that can credentialize any SAML service.

  • Pico Labs, my lab at BYU, demonstrated picos that acted as Hyperledger Indy agents and were able to connect to each other as well as other Indy agents like the AgentBook demo from Vonx. Picos are designed to act as digital twins or device shadows for the Internet of Things (IoT). Having agent-enabled secure messaging and credential exchange could be very useful for IoT products.

What got me excited about these demonstrations was that there were seven different organizations interoperably working in an ecosystem for credential exchange. While the rely on common libraries like Hyperledger Indy, they are separate code bases from different development teams that work together. This is a big development in the world of self-sovereign identity, demonstrating the reality of data exchange that is credential-based, secure, and private.


  1. You can read the proceedings of past Internet Identity Workshops on the IIW website.

Photo Credit: Liftoff of the SpaceX Falcon 9 rocket carrying NASA's TESS spacecraft. from NASA TV (CC0)

Decentralized Identifiers

Key and Label

Decentralized identifiers are one of several foundational technologies for building a metasystem for self-sovereign identity. I wrote about verifiable credentials and their exchange previously. Just like the Web required not only URLs, but also a specification for web page formats and how web pages could be formatted, self-sovereign identity needs DIDs, a protocol for creating DID-based relationships, and a specification and protocol for verifiable credential exchange.

Identifiers label things. Computer systems are full of identifiers. Variable names are identifiers. Usernames are identifiers. Filenames are identifiers. IP numbers are identifiers. Domain names are identifiers. Email addresses are identifiers. URLs are identifiers.1 Any time we use a unique (within some context) string to label something for quick reference, we're giving it an identifier. A computer system uses identifiers to correlate all the information it knows about a given thing. The mis-use of identifiers can lead to unwanted, even dangerous correlations.

Identifiers need context to be meaningful. For example, a string of digits might be a phone number, but we have no way of knowing for sure without context. Online context is often provided by a prefix. For example, is an email address, but is an account identifier.

Web-based identity systems have largely defaulted to using email addresses as identifiers. Everyone has one. And someone else has done the work of ensuring uniqueness since email addresses must be globally unique. But email addresses are also less than ideal as identifiers for several reasons:

  1. First, email addresses have a real, intended use (sending email) and so might change for reasons unrelated to their use as an identifier.
  2. Second, email addresses are generally correlatable. If you use the same email address for all your account identifiers, it's easy to track your activity at all those different places.
  3. Third, email addresses are generally administered by someone else who can take them away. Even if you use your own domain name, you're just renting that and may give up control in the future.
  4. Fourth, email addresses have limited global resolvability. All you can do is send an email message to the owner.
  5. Lastly, email addresses are reusable. If you stop using an email address the administrator of the email system may reassign it, decreasing security and privacy.

Decentralized Identifiers

Decentralized Identifiers, or DIDs, are a new kind of identifier that solves the problems outlined in the last section. As noted above, DIDs are one of the foundational technologies of self-sovereign identity. The DIDs specification is being developed inside the W3C Credentials Community Group. Let's explore the properties of DIDs and look at how they are formatted.

DID Properties

Decentralized identifiers should be implemented so that they have these important properties:

  • non-reassignable—DIDs should be permanent, persistent, and non-reassignable. Permanence ensures that the identifier always references the same entity. As a result, DIDs are more private and more secure than identifiers that can be reassigned such as a domain name, IP address, email address, or mobile number. Permanence is vital for user control and self sovereignty.
  • resolvable—DIDs are made useful through resolution. Resolution ensures that a DID is actionable. We'll discuss how DID resolution works in more detail below.
  • cryptographically verifiable—DIDs are designed to be associated with cryptographic keys and the entity controlling the DID can use those keys to prove ownership. That can happen in several ways. The result of resolving a DID may be cryptographically signed to ensure its integrity. The resolution also provides one or more public keys associated with the DID. Using cryptographic keys, the owner can prove they are in control of the DID. Parties who have exchanged DIDs can mutually authenticate each other and encrypt their communication.
  • decentralized— DIDs are designed to function without a central registration authority. Depending on the DID method specification for a given class of DIDs, they might also be created and updated outside the purview of any single party or entity, increasing censorship resistance.

DID Syntax

The syntax of a DID is fairly simple and designed to support different decentralization methods. The following diagram shows the primary, required components of a DID:

DID Syntax
DID Syntax (click to enlarge)

Each component is separated by a colon. The scheme, did, is fixed for all DIDs and alerts software seeing the DID that it is a DID. The method specifies how the DID is created, updated, and resolved. In the preceding figure, the method is sov. The method-specific identifier is an alphanumeric string that is guaranteed to be unique within the context of the method.

DID Resolution

Useful identifiers have a means of discovering what the identifier means. Discovery is performed in the manner outlined in the DID method. The DID specification outlines the necessary operations any method must implement. Different methods can support their own way of performing resolution using a specific blockchain or other storage system. The method outlines the way to create, retrieve, and update the DID and it's associate DID Document. For example, the did:sov method outlines how to create, lookup, and update the DID on the Sovrin ledger. A resolver can use the method to find the routines necessary for interacting with a given identifier. Methods allow a variety of systems to serve as repositories for DIDs.

DIDs are resolved to a DID Document. Resolution is the act of looking up the DID Document for a specific DID using the method given by the DID's method component. Taken as a whole, DID infrastructure functions as a global, decentralized key-value store where DIDs act as the keys and DID Documents are the values.

While the expectation is that these repositories will be decentralized, there's nothing in the specification that forces that. Any storage system could potentially have a DID method associated with it. Beware that some repositories may not be able to fulfill the non-reuse and permanence properties that are expected of DIDs.

DID Documents

DID Documents describe the public keys, authentication protocols, and service endpoints necessary to initiate trustworthy interactions with the identified entity. A DID Document is a JSON-LD document that contain the following six, optional components:

  1. The DID that points to the DID Document, identified by the key id.
  2. A list of public keys identified by the key publicKey.
  3. Lists of protocols for authenticating control of the DID and delegated capabilities identified by the key authentication.
  4. A set of service endpoints, usually URLs, that allow discovery of way to interact with the entity that the DID identifies identified by the key service.
  5. Timestamp indicating when the DID Document was created and updated for auditing the DID Document identified, respectively, by the keys created and updated.
  6. A digital signature for verifying the integrity of the DID Document identified by the key proof.

DID Documents can use other JSON-LD contexts to extend the DID Document and aid in discovery. For example, the data model could be extended to include the entity's RSS feed by referencing a JSON-LD context that describes RSS feeds.

The following is an example of a minimal DID Document taken from the DID specification2:

  "@context": "",
  "id": "did:sov:123456789abcdefghij",
  "publicKey": [{
    "id": "did:sov:123456789abcdefghij#keys-1",
    "type": "RsaVerificationKey2018",
    "controller": "did:sov:123456789abcdefghij",
    "publicKeyPem": "-----BEGIN PUBLIC KEY...END PUBLIC KEY-----\r\n"
  "authentication": [{
    "type": "RsaSignatureAuthentication2018",
    "publicKey": "did:sov:123456789abcdefghi#keys-1"
  "service": [{
    "id": "did:sov:123456789abcdefghij;exam_svc",
    "type": "ExampleService",
    "serviceEndpoint": ""
  "created": "2018-02-08T16:03:00Z",
  "proof": {
    "type": "LinkedDataSignature2015",
    "created": "2018-02-08T16:02:20Z",
    "creator": "did:sov:8uQhQMGzWxR8vw5P3UWH1ja#keys-1",
    "signatureValue": "QNB13Y7Q9...1tzjn4w=="

The DID Document is the root record for a decentralized identifier that can reference not only what's in the DID Document itself, but also any information from the service endpoints. This is accomplished by adding selectors, paths, query parameters, and fragments to the DID. With the exception of selectors, which are specific to DIDs, the syntax of these is familiar to anyone acquainted with the syntax of a URI.

The selector is used to identify a particular part of the DID Document. Selectors follow the DID itself and are delineated with a semicolon. In the preceding DID Document, there is only one service. Nevertheless, it can be selected using the following DID:


If the DID also includes a path, that is appended to the URL given in the service's serviceEndpoint attribute before the endpoint is called. For example, the following DID:


is equivalent to the following URL (based on the preceding example DID Document):

Through this mechanism, DIDs provide a permanent, resolvable identifier for any Internet service. For example, If one of the service endpoints in my DID Document is for email, then I can change my email address at will and anyone holding that DID will still be able to reach me. All I need to do is to be sure to update the DID Document when I change my email.

Public and Private DIDs

The preceding use case—putting my email in a DID Document—might be a privacy problem if I don't want my email to be publicly readable. Fortunately, not all DIDs are public. Identifiers can be, in the language of Kim Cameron (PDF), omnidirectional or unidirectional. Kim says in reference to his fourth law, Directed Identity:

A universal identity system must support both “omnidirectional” identifiers for use by public entities and “unidirectional” identifiers for use by private entities, thus facilitating discovery while preventing unnecessary release of correlation handles.

Sovrin supports public DIDs, written to the ledger and resolvable by all—omnidirectional identifiers. Sovrin also supports private DIDs, exchanged between parties to a relationship and resolvable only within that relationship—unidirectional identifiers.

The availability of private DIDs has significant advantages. Practically speaking, private DIDs allow for greater scalability of the DID resolution infrastructure since the vast majority of DIDs are private and those are resolved on a peer-to-peer basis rather than through access to some shared piece of infrastructure such as a distributed ledger.

More importantly, as Kim says about directed identity, private DIDs reduce access to correlatable identifiers by third parties increasing privacy protections. Private DIDs are critical infrastructure for a key part of the Sovrin architecture: peer relationships.

Peer Relationships

In On Sovereignty, I write:

The key to sovereignty is that all entities are peers. I have the same rights you do. The beauty of sovereignty isn't complete and total control, but rather balance of power that leads to negotiations about the nature of the relationships between various entities in the system.

In a world of identity systems based on decentralized identifiers, people do not create accounts at online service providers and then merely exist within that administrative system. Rather, people create relationships with other online entities and relate as peers.

To see how this works, imagine that you have recently been hired at a new job. Your new employer, ACME Corp, has a public DID that they use for issuing verifiable credentials. But as part of your employee onboarding, they and you will each create and exchange private DIDs. Because DIDs are cryptographically verifiable, you now each have a secure, channel to the other. You can use these DIDs to mutually authenticate when a connection is established, and to encrypt your communications.

This DID-based peer relationship is based on software agents that act for each party, maintain DIDs, resolve them, and facilitate cryptographically secure communication. The connection is truly peer-to-peer without some other platform in the middle. Apps and services built on top of these peer relationships can use these secure communication channels without being party to the private keys that secure them and ensure their integrity.

Since a DID Doc is JSON-LD and can be extended with other contexts, it can be extended to include other information. For example, you could extend the DID Document you share with your employer to include your home address and bank account information. Whenever those change, you'd update that DID Document and your employer would automatically see the changes.

Since the DID with selectors, fragments, and paths provides a way to resolve this information at will, the employer could merely store DIDs for that information rather than the information itself and resolve it at the local agent each time it is needed. Anyone breaking into their systems and stealing the reference wouldn't have permission to resolve the reference and get sensitive information. This provides the means for an employee, say, to share information with an employer that can be trusted and resolved at will without the employee having to issue a verifiable credential.

DIDs and the Identity Metasystem

In The Laws of Identity, I make the case for Sovrin being an identity metasystem—a universal foundation upon which other identity systems can be built. DIDs and DID Documents are a big part of the metasystem. Sovrin is designed to support the use of DIDs and DID Documents. Furthermore, Sovrin agents manage DID-based peer relationships, verifiable credential exchange, public and private DID resolution, and DID-based secure communication and authentication. DIDs allow Sovrin to be used by multiple parties for their own purposes.

Online Sovereignty

Decentralized identifiers and the attendant infrastructure that supports them provide a significant improvement over the ad hoc, email, and domain name based personal identifiers we've used for identity systems in the past. DIDs represent a universal addressing, abstraction, and verification layer for key pairs, endpoints, and any other information we wish to include in the DID Document. Layer verifiable credential exchange on top of this for multi-source identity and this constitutes a significant upgrade to online identity.

Because there's no central authority controlling DIDs and because people can issue private DIDs themselves, they constitute a truly decentralized means of not only creating identifiers, but using them for mutual authentication, privacy preservation, and secure communication of almost any information parties need to share.

Speaking of DIDs, DID Documents, and Verifiable Credentials in an email to Project VRM mailing list, Joe Andrieu, put it like this:

The win is that these new technologies let us engage in digital society with identifiers we create and control--rather than those gifted or rented to us from a third party. Combined with an open system of verifiable attributes, we can also control the selective disclosure of certain "provable" assertions (provable in the sense that some entity like the DMV stands behind the assertion). Collectively, the identifiers and attributes constitute a full and verifiable identity in the common sense we imagine. For the first time, we can come to the party as a peer of the realm instead of a serf.

An identity metasystem that can provide real peer relationships is critical to protecting individual privacy, creating real security, and, more importantly, supporting human dignity. DIDs are a key part of the architecture.


  1. All of these may be other things as well like addresses or names, but they're still identifiers.
  2. I've modified this DID Document slightly to support the examples I want to make.

Photo Credit: Grey Color Keychain Mat Metal Key Shiny from Unknown (CC0 Public Domain)

The Laws of Identity

Law Books

In 2005, Microsoft's Chief Identity Architect, Kim Cameron wrote an influential paper called The Laws of Identity (PDF). Kim had been talking about and formulating these laws in 2004 and throughout 2005. It's no coincidence that Internet Identity Workshop got started in 2005. Many people were talking about user-centric identity and developing ideas about how we might be able to create an identity layer for the Internet. Fifteen years later, we're still at it, but getting closer and closer all the time.

The Internet was created without any way to identify the people who used it. The Internet was a network of machines. Consequently, all the identity in Internet protocols is designed to identify machines and services. People used the Internet through some institution (their company or university) and were part of that institution's administrative identity system. This can still be seen in the format of email addresses that identify both recipient and sender as someone@someplace. As the Internet grew to include people who weren't formally associated with an institution, every Web site and service created their own administrative identity domains. The result is the fractured plethora of identifiers, policies, and user experiences that constitute digital identity in 2019.

An Identity Metasystem

In his paper, Kim asks why it's so hard to create an identity layer for the Internet and answers his own question:

Mainly because there is little agreement on what it should be and how it should be run. This lack of agreement arises because digital identity is related to context, and the Internet, while being a single technical framework, is experienced through a thousand kinds of content in at least as many different contexts—all of which flourish on top of that underlying framework. The players involved in any one of these contexts want to control digital identity as it impacts them, in many cases wanting to prevent spillover from their context to any other. (emphasis in original)

Kim's answer is not a new identity system, but rather an identity metasystem. He describes the metasystem:

...different identity systems must exist in a metasystem. It implies we need a simple encapsulating protocol (a way of agreeing on and transporting things). We also need a way to surface information through a unified user experience that allows individuals and organizations to select appropriate identity providers and features as they go about their daily activities. The universal identity metasystem must not be another monolith. It must be polycentric (federation implies this) and also polymorphic (existing in different forms). This will allow the identity ecology to emerge, evolve and self-organize.

This is an excellent description of Sovrin. Sovrin is not a company or an identity provider. Rather, Sovrin is a set of protocols and a network that allows multiple identity providers (polycentric) to provide identity credentials to anyone for any purpose (polymorphic).

Let's look at how Sovrin stacks up as a universal identity metasystem that supports Kim's laws of identity.

1. User Control and Consent

Technical identity systems must only reveal information identifying a user with the user’s consent.

As a self-sovereign, multi-source identity system, Sovrin is architected so that the identity owner is structurally part of exchanging verifiable credentials1. This is enforced by the default to use non-correlatable, decentralized identifiers (DIDs) to establish relationships between identity owners, credential issuers, and credential verifiers. Since there is no universal identifier in Sovrin, the identity owner is the only legitimate point of correlation.

The ledger plays a role in putting the identity owner in control by providing a decentralized means for the credential verifier to obtain the information it needs to validate the legitimacy of the credential. As a result, the system avoids creating a back channel from verifier to issuer that might be used to exchange information about the identity owner without her consent.

The only personally identifying information (PII) available to the credential verifier is the information that the identity owner has consented to provide to the verifier.

Besides the control that credential exchange provides identity owners, people are not locked into a single provider for tools. They can choose from multiple, interoperable tools to use their Sovrin-based credentials. Sovrin is a public network that anyone can use. The network is architected to resist censorship that might deny people the control they need to use their digital credentials however they like.

2. Minimal Disclosure for a Constrained Use

The solution which discloses the least amount of identifying information and best limits its use is the most stable long term solution.

In Sovrin, credentials are issued to identity owners. But identity owners do not share the credential with the verifier. Presenting the entire credential would reveal more information than is necessary. Instead, the identity owner presents a zero-knowledge proof of the information the verifier needs. The ability to limit the information presented from a credential is important to maintaining privacy through the principle of minimal disclosure.

The credential verifier can verify the credential proof by looking at the credential definition on the ledger, retrieving the public DID and associated DID Document of the issuer, and using the public key in the DID Document to check the signature of the credential to ensure it hasn’t been tampered with. The verifier can also cryptographically verify that the credential was issued to the identity owner. As part of making a proof from the credential, the identity owner also proves that it has not been revoked by referencing the revocation registry, which is also available on the ledger.

3. Justifiable Parties

Digital identity systems must be designed so the disclosure of identifying information is limited to parties having a necessary and justifiable place in a given identity relationship.

As a multi-source identity system, Sovrin provides the means for each party in an identity transaction to play their role without the aid or assistance of an intermediary. Consider the following diagram that shows Alice receiving a credential from her employer and proving information about her employment to her bank.

Credential Flow for Alice Obtaining a Loan
Credential Flow for Alice Obtaining a Loan (click to enlarge)

The only parties to the transaction are the three that need to be part of the transaction: Alice, her employer, and her bank. No other person or institution is party to the transaction. The ledger is run by validator nodes and one of more of those nodes might see the reads and writes to the ledger, but these are not correlatable and involve the public identifiers and information that the credential issuer used to create the credential definition.

4. Directed Identity

A universal identity system must support both "omni-directional" identifiers for use by public entities and "unidirectional" identifiers for use by private entities, thus facilitating discovery while preventing unnecessary release of correlation handles.

Sovrin supports both public ("omni-directional" in Kim's terminology) and private ("unidirectional") decentralized identifiers. Public DIDs are written to the ledger and available for anyone to look up. Private DIDs are not written to the ledger, but rather maintained in pairwise relationships between parties in peer-to-peer agents that are under the control of identity owners.

In the preceding diagram, the credential issuer, Alice's employer, has a public DID. A public DID is necessary to issue credentials since the verifier will want to look up the issuer as part of verifying the credential. The bank likely also has a public identifier but it plays no role in this credential exchange. Alice has exchanged private DIDs with both her employer and the bank. These private DIDs form the basis for the cryptographic relationship that Alice has with these institutions. The DIDs that the employer and bank give to Alice are also private, meant just for the relationship with Alice. The employer and bank created private DIDs to represent themselves to Alice, rather than using their public DIDs.

The use of public and private DIDs allows public discovery where necessary (the credential issuer) and prevents the correlation of records that credential issuer and verifier might have about the identity owner, this protecting her PII. The parties in a relationship can use the private DIDs and their associated public keys to mutually authenticate. Private DIDs are GDPR compatible since they are not shared on an immutable ledger.

5. Pluralism of Operators and Technologies

A universal identity system must channel and enable the inter-working of multiple identity technologies run by multiple identity providers.

Sovrin is a multi-source identity system. This means that rather than a single-source provider of identity credentials, as has been the norm for the Internet, anyone can issue any kind of credential for any purpose. Sovrin doesn't give you an identity—it's not an identity provider. Rather Sovrin enables a rich ecosystem of third party credentials, just like in the physical world. These credentials can be mixed together to easily prove things to others.

Credential schemas can be authored by anyone. And anyone can use an existing schema to create a credential definition which combines the schema, issuer DID, and revocation registry ID. This means that credentials are flexible and decentralized. No one is in charge of deciding what credentials are allowed or disallowed. No central party says which credentials are valid and which are not. Instead, each issuer decides what to issue, each identity owner decides which credentials to carry and present, and each verifier decides which credentials to trust.

Credentials are structured using a standard and exchanged using open protocols. Anyone can build software to use these standards and protocols or build them into their own systems. As a result, Sovrin presents an identity metasystem that anyone can use for any purpose and integrate with any tool or identity system they already use.

Beyond credentials, Sovrin's architecture supports independent software agents to hold and process credentials as well as to perform identity transactions on the identity owner's behalf. These agents interoperate directly with each other as peers. Sovrin specifies the protocols that agents use so that agents from different vendors can work together and to support substitutability.

6. Human Integration

The universal identity metasystem must define the human user to be a component of the distributed system integrated through unambiguous human-machine communication mechanisms offering protection against identity attacks.

As we've seen, the identity owner is a structural part of the identity transactions in Sovrin. Sovrin is architected to make by-passing her very difficult.

Identity owners don't manage keys but manage relationships and credentials, familiar artifacts from the physical world. Key management is handled by the software, below the interface. The identity owner can see, manage, add, delete, select, and share credentials on their device in the same manner they do other digital artifacts like files and folders. Rather than a world of user names and passwords, identity owners work with digital representations of the same things they use for identity transactions in the physical world.

People establish Sovrin relationships within contexts they already understand (e.g. their bank's website or their employer's HR system). They store those relationships in an app that functions like an address book on their phone. The app also stores credentials, another familiar item rendered digitally in the app. Because these artifacts and the act of exchanging credentials is analogous to what people do in their every day lives, the process of doing so with Sovrin is familiar as well.

7. Consistent Experience Across Contexts

The unifying identity metasystem must guarantee its users a simple, consistent experience while enabling separation of contexts through multiple operators and technologies.

The user experience with Sovrin is dictated by the protocol. Regardless of who identity owners are exchanging credentials with or what software they're using, the process is unified and consistent. The user experience is supported by the actors and roles in the protocol and the actions that each can take. Further, the open source code provides reference code for the applications that helps vendors of products that participate in credential exchange to create consistent, interoperable experiences.

At the same time, the unified experience supports multiple credentials from multiple parties who make decisions in a decentralized way. A person can mix verifiable claims from multiple credentials to create an identity transaction that is right for any particular online context. By seeing familiar digital artifacts, selecting, mixing, and sharing them in that context, the identity owner can see exactly what is being requested and make informed choices about what to share without excessive effort.

Sovrin as an Identity Metasystem

Kim concludes:

Putting all the laws together, we can see that the request, selection, and proffering of identity information must be done such that the channel between the parties is safe. The user experience must also prevent ambiguity in the user‟s consent, and understanding of the parties involved and their proposed uses. These options need to be consistent and clear. Consistency across contexts is required for this to be done in a way that communicates unambiguously with the human system components.

As users, we need to see our various identities as part of an integrated world which none the less respects our need for independent contexts.

Sovrin is architected to meet these needs and provide the kind of unified digital identity experience that Kim envisioned. When I read what Kim wrote almost 15 years ago, I get the feeling that he was a being from the future, telling us things that most of us were not prepared to understand for some time. I know I wasn't. The concepts and ideas that Kim laid out in the Seven Laws and follow-on work (PDF) provide a blueprint for understanding how we can really solve the problem of identity on the Internet.

Sovrin is the identity metasystem that Kim wrote about. I believe that creating and using an identity metasystem with the properties that Kim describes will have far reaching economic and functional impact. More importantly, I think the implications that it has for privacy, security, and human freedom and dignity cannot be overstated. When we look back, I think we'll all be surprised that it took us so long to build. I urge you to join us in making it a reality.

End notes:

  1. The word credential is used here where Kim used the word "claim." Technically a credential is a collection of claims. The credentials might be the kinds of things we typically think of as a credential, but might also be things that aren't often thought of that way like an airline boarding pass or a prescription for medicine. The world is full of credentials.

Photo Credit: Law Books from Max Pixel (CC0 1.0)

Verifiable Credential Exchange

I realized last week that I'd never explained verifiable credential exchange as a stand-alone topic—it was always buried in something else.

Multi-source identity (MSI) depends on issuing, exchanging, and verifying digital credentials. The specification for verifiable credentials is being formulated by the World Wide Web Consortium’s Verifiable Credentials Working Group. Verifiable credentials provide a standard way to express credentials in a way that is cryptographically secure, privacy respecting, and automatically verifiable.

Credentials are defined by their issuer in a credential definition. The credential definition links the public decentralized identifier (DID) of the issuer, the schema for the credential, and a revocation registry for the credential. The definition, public DID, schema, and revocation registry are all stored on a distributed ledger that is used for decentralized discovery. (See What Goes on the Ledger (PDF) for more detail on these.)

Credential exchange is the process by which credentials are issued, held, presented, and verified. Credentials are exchanged peer-to-peer by software called "agents." The specific details of how this works technically is defined in Indy agent protocol. Agents create relationships in this peer-to-peer network by exchanging DIDs and their associated public keys.

Here's an example of how credential exchange works. Suppose Alice is applying for a loan at her local bank. The bank requires proof that Alice is employed and makes at least $70,000 per year. Alice has pre-existing relationships with her employer and her bank, meaning her agent is connected to their agents via an exchange of DIDs. Alice’s employer has issued an employment credential that includes her employment status and her current salary. It might also include many other attributes related to Alice’s job. As shown below, Alice holds this credential in her agent. She can present the credential to prove to the bank that she is employed and makes more than $70,000.

Credential Flow for Alice Obtaining a Loan
Credential Flow for Alice Obtaining a Loan (click to enlarge)

When Alice proves her employment status to the bank, she doesn’t present the entire credential since doing so would reveal more information than is necessary. Instead, Alice presents a zero-knowledge proof of just the information the bank needs. The ability to limit the information presented from a credential is important to maintain privacy through the principle of minimal disclosure.

Alice’s bank can verify the credential proof by looking at the credential definition on the ledger, retrieving the public DID and associated DID Document of the issuer, and using the public key in the DID Document to check the signature of the credential to ensure it hasn’t been tampered with. The bank can also cryptographically verify that it was issued to Alice. As part of making her proof from the credential, Alice also proves that it has not been revoked by referencing the revocation registry, which is also available on the ledger.

In multi-source identity, a particular credential is not intrinsically true. Rather each verifier determines who and what they will trust by relying on the attestations of other parties. Thus, truth is established through a preponderance of evidence. How much evidence is needed for a situation depends on the risk, something the verifier determines independently.

For example, in the previous scenario, if the bank does not already know the public DID of the employer, they could validate it in several ways. The most obvious is to interrogate the endpoint in the employers DID Document and ask for proof that they are a legal business and any other information they need to trust the employer. The employer could use credentials they have to prove this to the bank, or they could do it out of band. Once the bank knows to trust the public DID of the employer, this information could be cached according to the policies of the bank.

The trust model for verifiable credentials has five important characteristics that mirror how credentials work in the offline world:

  • Credentials are decentralized and contextual. There is no central authority for all credentials. Every party can be an issuer, a holder (identity owner), or a verifier. Verifiable credentials can be adapted to any country, any industry, any community, or any set of trust relationships.
  • Credential issuers decide on what data is contained in their credentials. Anyone can write credential schemas to the ledger. Anyone can create a credential definition based on any of these schemas.
  • Verifiers make their own trust decisions about which credentials to accept—there's no central authority who determines what credentials are important or which are used for what purpose.
  • Verifiers do not need to contact issuers to perform verification—that's what the ledger is for. Credential verifiers don't need to have any specific technical, contractual, or commercial relationship with credential issuers.
  • Credential holders are free to choose which credentials to carry and what information to disclose. People and organizations are in control of the credentials they hold (just as they are with physical credentials) and determine what to share with whom. This is sometimes referred to as self-sovereign identity (SSI).

Multi-source identity is composed of credentials from multiple sources. In addition to her relationship with her employer and bank, Alice likely has a relationship with the state, and holds credentials they issue representing her birth certificate and driver’s license. She might hold credentials from her university representing her transcript. The list of potential credentials that Alice holds is long and depends on her relationships online and offline. She could have hundreds of relationships and associated credentials in her wallet. She can use any of these, in any combination, to prove things about herself (with minimal disclosure) to any other party who accepts them.

Decentralized credential exchange is not new—we've been doing it in the physical world for centuries. But doing it online is novel. Decentralized digital credential exchange gives people and organizations the freedom and autonomy to create authorization regimes that meet their particular needs. Furthermore, credential holders have autonomy and choice in whether to participate. The result is a flexible identity architecture that covers thousands of use cases, even ad hoc use cases, while supporting choice and privacy for identity owners.

Verifiable credential exchange enables online identity transactions that are nearly impossible to imagine using the single-purpose, IdP-based identity systems of the past. The Internet enabled a rich, decentralized ecosystem of message exchange that could never have been supported by the walled gardens of Compuserve and AOL. Similarly, self-sovereign, multi-source identity enables a richer, decentralized ecosystem of identity transactions than can ever be realized with the single-source identity systems we've used to date. Self-sovereign, multi-source identity enables an Internet for Identity.

The Sovrin Ecosystem

People often ask me how Sovrin relates to Evernym or Hyperledger Indy. It can be confusing, so I created a diagram that seems to help. First a few definitions:

  • Sovrin Foundation—The Sovrin Foundation is an international non-profit organization supporting self-sovereign identity through a global, decentralized network. I've discussed the Foundation, it's mission, and organization at some length in a previous blog post.
  • Evernym, Inc.—Evernym is a commercial software vendor that developed the initial technology for Sovrin and continues to be a large contributor to the open source code that Sovrin is based on.
  • Hyperledger Indy—Indy is one of the open source code projects in Hyperledger, an open source code effort sponsored by the Linux Foundation.
  • Sovrin Community—The community is the heart of what makes Sovrin work and comprises identity owners, developers, stewards, businesses, and other organizations, all in multiple roles and with varied interests.
Relationship between Sovrin Foundation, Evernym, and Hyperledger
Relationship between Sovrin Foundation, the Sovrin community, Hyperledger Indy, software vendors, and service providers. (click to enlarge)

The preceding diagram shows the relationships between these and other organizations:

  • Sovrin Foundation is the sponsor of the Hyperledger Indy open source project. The Sovrin Network runs code from Indy.
  • Evernym and other organizations build products that run on the Sovrin Network. For example, Evernym is building the wallet for use with Sovrin and a commercial enterprise-grade verifiable credentialing system called Verity. The Government of British Columbia is building software to use Sovrin credentials for business licensing. These commercial organizations also provide services, like agencies, to the Sovrin community. Developers at these organizations contribute code to Hyperledger Indy.
  • Hyperledger Indy houses the open source code for the Sovrin Network and provides collaboration services for Sovrin, Evernym, and others working on Indy code. Indy relies on volunteer contributions from the Sovrin Community.
  • Sovrin Community supports and is supported by the Foundation, contributes to Indy, and provides services to or uses services from the various software vendors and agencies.

Even though Sovrin is only a few years old, this ecosystem is making great progress toward making self-sovereign identity a reality. Here are a few accomplishments from just the last year:

  • The Sovrin network now boasts stewards on every continent except Antarctica. There are over 60 stewards representing organizations large and small from around the world.
  • The Sovrin network is running code contributed by over 150 developers who made over 20K contributions just in the last 12 months.
  • The Sovrin Governance Framework has undergone a major overhaul and represents the very best thinking from contributors around the globe in how a self-sovereign identity network should be governed.
  • Dozens of organizations from around the world are conducting pilots or proofs of concept to explore how Sovrin can help them better serve and connect to their customers.

All of this adds up to an extraordinary, vital ecosystem dedicated to promoting self-sovereign identity, defining the processes, protocols, and specifications to make it happen, and building a network that makes it a reality.

Decentralization in Sovrin

Queen and Attendents

Decentralized architectures require that care is taken in each component or layer to ensure that the resulting system will not contain hidden weaknesses. That doesn't just apply to the system itself, but also to the ways it is governed. And all decentralized systems are governed. The governing might be ad hoc or hidden, but it's there.

I've written a lot about distributed ledgers, Sovrin, governance, and decentralization over the past several years. Here's a partial list:

You can see this topic has been on my mind. The remainder of this post is going to focus on the decentralized nature of the Sovrin Network.

As a hybrid system, the Sovrin Network benefits both from having a blockchain-based ledger and from having formal governance. Both of these are important for Sovrin to thrive and meet its objectives. And, contrary to what you might think, governance helps in achieving a public, decentralized system that has real utility.

The Sovrin Network

Our goal is for the Sovrin Network to be an open, public, decentralized utility for digital identity. Those three adjectives deserve some explanation:

  • open—The Sovrin network is based on the open-source Hyperledger Indy project. That is important, but it's not sufficient. The governance of the Sovrin Network should also be open. This extends to decisions about the code, who runs it, and the features that it enables.
  • public—Anyone should be able to access and use Sovrin for any purpose that it supports. Public access is a foundational element for self-sovereignty because it avoids gatekeepers that might censor some transactions. This applies not only to reading information from the ledger, but also authoring ledger transactons.
  • decentralized—no single entity should represent a single point of failure. This doesn't just apply to the availability of the network, but also the ability of people to use the network.

The Sovrin protocol is layered as shown in the following diagram.

The Three Layers of the Sovrin Network
The Three Layers of the Sovrin Network (click to enlarge)

Each of these layers builds upon the one below. Consequently, it's important that each layer have appropriate support for decentralized operation to ensure that the network supports self-sovereignty.

The Ledger Layer

The Sovrin Network is based on a distributed ledger. The ledger is a small, but critical, part of Sovrin's overall functionality. Every identity system needs a way to discover what identifiers mean—if you get an identifier, you want to look it up. For identity systems, that has traditionally been implemented as a centralized database controlled by a single entity. For Sovrin to be decentralized, it must have a decentralized means of discovery. The Sovrin ledger provides that.

Sovrin's ledger is a hybrid combining known validator nodes with public access. Because of this architecture, Sovrin is difficult to categorize in the various discussions of permissioned and permissionless blockchain systems. One common refrain is "blockchains don't need trust (governance) frameworks." Another goes "the point of blockchain is to avoid governance." Those might be true in some architectures, but they don't apply to Sovrin, as I'll discuss below.

Sovrin never stores personally identifying information, encrypted or not, on the ledger, unlike many other blockchain-based identity systems. Rather Sovrin uses the ledger for Decentralized Identifiers (DIDs), schema definitions, credential definitions, and revocation registries. Without a ledger to store these, Sovrin would have a single point of failure for these critical objects. For more information, see What Goes on the Ledger (PDF).

Objects like a DIDs are written to the ledger by transaction authors and validated by transaction validators. These functions are separate. Because the Sovrin Network is public, anyone can be a transaction author. But only organizations who function as Sovrin Stewards can validate transactions. Validation is done using a modified Redundant Byzantine Fault Tolerance algorithm implemented as Indy Plenum.

If the ledger is the basis for decentralized discovery in Sovrin, then we should ensure that no single organization controls the ledger and that it is protected from being taken down or corrupted by a single or even a few entities. Sovrin is designed to be censorship resistant. No company or special interest can control who can use the protocol. Sovrin is available for any application or purpose. And the priority of transaction validation is fair. Public authorship of Sovrin transactions on a ledger represents the best means available to combating censorship.

Validation on the Sovrin ledger is based on a known set of nodes run by the Stewards. This architecture was chosen to reduce the resource usage (and hence, cost) of the ledger. We have designed the ledger and its governance to ensure that the ledger is public, open, and decentralized despite the presence of known validators.

One key idea in decentralized systems is that different parts of the system are under the control of different organizations. Censorship resistance requires that even though Stewards must meet certain requirements to participate, we must still assume that any node might be hostile because of a hack or other circumstances beyond the control of the Steward. A distributed ledger provides this important property and is, consequently, the right data structure for this.

In addition, using a blockchain ensures that multiple organizations are responsible for a shared space for discovery. Losing one or even several Stewards would not impact the ability of people to manage and use their identifiers on Sovrin. One of Sovrin's guiding principles is diversity of validators to protect this vital function.

Some might be concerned that Sovrin Foundation itself holds a special place and thus represents a single point of failure. While it's true that the Foundation administers the governance framework and manages the open source project, the Foundation does not run the Sovrin Network. Consequently, it could cease to exist and the network would continue operating. In the case of the ledger itself, the Stewards would keep operating the Network and re-organize. The open source project would continue, as open source projects do, because the code is available to and maintained by people rather than a specific organization.

Because transaction authoring is a public function, the use of a ledger also ensures that people can access, write, and update identifiers without being subject to gatekeepers. Even if those gatekeepers are friendly, they might restrict access to certain people, certain groups, or certain jurisdictions due to a hack or other circumstances beyond the control of the gatekeeper.

The Agent Layer

Agents are a core element of the Sovrin architecture. Since Sovrin does not store personally identifying information on the ledger, people need a place to hold, manage, and use keys and credentials. Agents fill that role. Sovrin's architecture supports both cloud and device agents. Most people will have more than one. Sovrin identity owners usually have at least two agents, one on a device and one in the cloud The device agent is connected to an app and contains a wallet for storing keys and credentials.

Sovrin agents operate independently from each other in a peer-to-peer (heterarchical) topology. Agents communicate with each other for DID and credential exchange without an intermediary. Neither do they need the ledger to communicate. Communication between agents is done via signed and encrypted messages. The two agents in a peer relationship authenticate each other using the keys they exchanged when they established a relationship. Each agent has its own keys and keys are never copied between agents.

Clearly device agents and wallets are not centralized because they store their keys and credentials on the device. The cloud agent can be run by a service provider called an agency or self-hosted. Most people will opt to use an agency. There can be multiple agencies and agent operation is standardized so that users can switch agencies.

Further, the agency does not have access to what's in the agent. There are no master keys. So, barring a code problem that opens a security hole, there's no honey pot. We believe agent code should be open source to reduce security risk by getting as many eyes on the problem as possible.

The peer-to-peer architecture of agents and their availability from multiple agencies creates a decentralized system for storing, managing, and using keys and credentials. This not only is a boon to identity owner privacy and autonomy, it also ensures that Sovrin can scale to trillions of relationships.

The Credential Exchange Layer

The top layer in Sovrin is where credential exchange happens. Credential exchange is central to how Sovrin works. Sovrin does not have "identity providers" because anyone can be the source of their own identity. Your digital identity is made from credentials from multiple sources. I call this multi-source identity. You might have a Sovrin-based relationship1 with your bank. They could provide a Sovrin credential stating you're a customer and maintain a certain balance. Similarly, you could have a relationship with your employer and an employer-issued credential stating you're an employee. And you likely have a relationship with the state, and credentials they issue representing your birth certificate or drivers license. The list goes on. You could have hundreds of relationships and associated credentials in your wallet. You can use any of these, in multiple configurations, to prove things about yourself (with minimal disclosure) to any other party who accepts them.

Credential exchange is done peer to peer via agents. Agents use the ledger in various ways in credential exchange. Issuers use it to write public DIDs, credential definitions, schema, and revocation registries. Credentials holders use the ledger to prove a credential they're presenting hasn't been revoked, among other things. Verifiers use the ledger to check the public DIDs of the credential issuer and look up schema and credential definitions. Because of the ledger, credential issuers don't see when a verifier verifies a credential, a further boon to identity owner privacy.

Sovrin's trust model for verifiable claims has five important and desirable properties that all underscore its support for decentralization and personal autonomy:

  1. Credentials are decentralized and contextual. There is no central authority for all credentials. Every party can be an issuer, an owner, and a verifier. The system can be adapted to any country, any industry, any community, any set of credentials, or any set of trust relationships.
  2. Credential issuers decide on what data is contained in their credentials. Sovrin allows anyone to write credential schemas to the ledger. Anyone can create a credential definition based on any of these schemas.
  3. Verifiers make their own trust decisions about which credentials to accept—there's no central authority who determines what credentials are important or which are used for what purpose.
  4. Verifiers do not need to contact issuers to perform verification—that's what the ledger is for. Credential verifiers (the people or organizations relying on a credential) don't need to have any technical, contractual, or commercial relationship with credential issuers (the people or organizations making the credential).
  5. Credential holders are free to choose which credentials to carry and what information to disclose. People and organizations are in control of the credentials they hold (just as they are with physical credentials) and determine what to share with whom.

Decentralized credential exchange is not new—we've been doing it in the physical world for centuries. But it is new online. Decentralized credential exchange gives people and organizations the freedom and autonomy to create authorization regimes that meet their particular needs. Furthermore, credential holders have autonomy and choice in whether to participate. The result is a flexible system that covers thousands of use cases while supporting choice and privacy for identity owners.

Decentralized, Self-Sovereign Identity

The architecture of Sovrin, at all three levels of operation, creates a decentralized identity system that has the same decentralized properties as the Internet:

  • No one owns it
  • Everyone can use it
  • Anyone can improve it

The lack of a decentralized, heterarchical, and interoperable identity system has led to an environment where the services most people use online are a lot more centralized than the Internet they exist upon. Sovrin corrects this by providing the means for people to exercise greater autonomy and freedom. Decentralized identity is the key to creating a more decentralized Web—a Web that flexibly supports the kind of ad hoc interactions people have with each other all the time in real life.

Without peer-based interactions and public access, Sovrin would not be self-sovereign. By supporting control of identity information by people, Sovrin creates a self-sovereign identity environment. Self-sovereignty requires that the parties to the credential transaction behave as peers. In traditional identity systems the rights of the so-called "identity subject" are subordinate to those of the identity provider. In Sovrin, every player independently determines the role they'll play, who they trust, and what they will believe.


  1. When I say "relationship" that means that both sides have an agent and have exchanged DIDs to create a pairwise pseudonymous relationship.

Photo Credit: Bees in a bee hive from USDA (CC BY 2.0)

Multi-Source and Self-Sovereign Identity

A Wallet Holding Credentials

The world is full of credentials. Some, like a driving license, an employee ID card, a passport, or a university diploma are widely recognized as such. But many other things are also credentials: a store receipt, a boarding pass, or a credit score, for example. Credentials, designed properly, allow verifiable data to be employed in workflows without centralized hubs, point-to-point integrations, or real-time communication between the various players. Credentials enable decentralized, asynchronous workflows.

The Issuer/Holder/Verifier Trust Triangle
The Issuer/Holder/Verifier Trust Triangle

Multi-source identity (MSI) allows multiple credentials from multiple providers to be brought to bear, flexibly and conveniently, in a situation where trusted attestations are needed for the participants in a workflow to make progress. In MSI, there are three players: credential issuers, credential holders, and credential verifiers. Any person or organization can play any or all of the roles.

  • Credential issuers determine what credentials to issue, what the credential means, and how they'll validate the information they put in the credential.
  • Credential holders determine what credentials they need and which they'll employ in workflows to prove things about themselves.
  • Credential verifiers determine what credentials to accept and who to trust.

Because of these features, MSI is decentralized. In contrast, traditional identity systems have a single identity provider (IdP) who administers an identity system for their own purposes, determines what attributes are important, and decides which partners can participate.

In MSI, a particular credential is not intrinsicly true. Rather each verifier determines who and what they will trust by relying on the attestations of other parties. Thus, truth is established through a preponderance of evidence. How much evidence is needed for a situation depends on the risk, something the verifier determines independently.

Self-sovereign identity means the individual or organization controls and manages their identity. Multi-source identity becomes self-sovereign identity (SSI) when the individual is able to control the credentials and use them in a privacy-preserving manner whenever and where ever they want. Privacy is a critical feature of SSI because without privacy, there is no control. In SSI, the identity owner must be able to control who sees what and that means that privacy is a fundamental property of the architecture for SSI.

SSI also implies that the parties to the credential transaction behave as peers. In traditional identity systems the rights of the so-called "identity subject" are subordinate to those of the identity provider. In SSI, every player independently determines the role they'll play, who they trust, and what they will believe. As we've seen, in SSI, an identity owner holds credentials from multiple providers and can use them where ever she wants. While these credentials can be revoked individually, the identity owner still controls her own identity wallet and all the other credentials she has collected.

Self-sovereign identity represents a monumental shift in how identity functions on the Internet. Internet identity systems have traditionally only supported a limited set of attributes and required prior agreement and custom integration. SSI frees Internet identity from this narrow view by introducing support for the exchange of credentials by individuals and organizations acting as peers. The result will be an Internet identity regime that is more flexible, more secure, more private, less burdensome, and less costly.

Photo Credit: A picture of a wallet from TheArmadillo (CC BY-SA 3.0)