science

Verifiable credentials

Verifiable credentials is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Verifiable credentials rather than just read about it. In short: Verifiable credentials (VCs) are digital credentials which follow the relevant World Wide Web Consortium open standards. They can represent information found in physical credentials, such as a passport or license, as well as new things that have no physical equivalent, such as ownership of a bank account.

Key takeaways

Verifiable credentials belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Verifiable credentials to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Verifiable credentials from memory before moving on to harder problems.

Reference excerpt

Verifiable credentials (VCs) are digital credentials which follow the relevant World Wide Web Consortium open standards. They can represent information found in physical credentials, such as a passport or license, as well as new things that have no physical equivalent, such as ownership of a bank account. They have numerous advantages over physical credentials, most notably that they're digitally signed, which makes them tamper-resistant and instantaneously verifiable. Verifiable credentials can be issued by anyone, about anything, and can be presented to and verified by everyone. The entity that generates the credential is called the Issuer. The credential is then given to the Holder who stores it for later use. The Holder can then prove something about themselves by presenting their credentials to a Verifier.

Standards

Trust model The holder of a verifiable credential operates in a triangle of trust, mediating between issuer and verifier.

The issuer trusts the holder The holder trusts the verifier The verifier trusts the issuer Any role in the triangle can be played by a person, an institution, or a machine. Note that because verifiable credentials can be created by anyone, the verifier decides if they trust the issuer.

Decentralization The VC model places the holder of a credential at the center of the identity ecosystem, giving individuals control of their identity attributes. The W3C VC model parallels physical credentials: the user holds cards and can present them to anyone at any time without informing or requiring the permission of the card issuer. Such a model is decentralized and gives much more autonomy and privacy to the participants. This contrasts with the federated identity management (FIM) model, as adopted by SAML and OpenID Connect, which place the identity provider (IdP) in the central role as the dispenser of identity attributes and the determiner of which Service Providers (SPs) it will give them to. In the federated model, the IdP knows every SP that the user visits.

Verifiable Credentials Data Model 1.0 The data model for verifiable credentials is a World Wide Web Consortium (W3C) Recommendation, "Verifiable Credentials Data Model 1.0 - Expressing verifiable information on the Web", published 19 November 2019.

Composition Verifiable Credentials may be expressed using JSON and is typically composed of:

Context Issuer Issue timestamp Expiry timestamp Type Subject Subject identity attributes Cryptographic proof to ensure the integrity and authenticity of the VC

Aliases The VC context, defined using the @context JSON property, is a JSON-LD construct that allows user friendly terms to be used for JSON properties. According to the VC data model, the value of many properties must be a URI. Whilst these are globally unambiguous, (important for a global data model), they are not user-friendly. Consequently, the @context property allows short-form, user-friendly aliases to be defined for each URI. This makes it much easier, and more user-friendly, to specify VCs. An example is given below.

W3C VCs are extensible. Any new property can be added to VCs, as determined by the issuer. Standard properties have been defined specifically as extension points. These include the following:

terms of use - restrictions placed on the use of the VC by the issuer schema - defines VC contents evidence - information collected by issuer about the subject and/or attributes before issuing the VC status - pointers to where a verifier can discover the status of a VC (e.g., whether it has been revoked).

Subject The holder of a VC does not always have to be the subject of the credential. It is expected that most users will hold their own VCs, i.e., the holder and the subject will be the same entity. This need not always be the case. For example, when the VC subject is an infant, and the VC is a birth certificate, the holder may be one or both parents.

Proofs No proof mechanism is standardized but the data model is flexible enough to support various existing cryptographic mechanisms, such as digital signatures. Proof mechanisms that are in use include: JSON Web Tokens with JSON Web Signatures, JSON-LD proofs, and zero-knowledge proofs using schemes such as IBM's anonymous credentials.

Transport Various protocols are specified for carrying VCs from the issuer/IdP to the holder, and the holder to the verifier. Examples include:

Aries RFC 0036: Issue Credential Protocol 1.0., and Aries RFC 0037: Present Proof Protocol 1.0 David W Chadwick, Romain Laborde, Arnaud Oglaza, Remi Venant, Samer Wazan, Manreet Nijjar "Improved Identity Management with Verifiable Credentials and FIDO", IEEE Communications Standards Magazine Vol 3, Issue 4, Dec 2019, Pages 14–20 None of these protocols has become standardized. Many people who are experimenting with VCs use HTTPS to carry VCs between the various parties.

Criticisms and concerns The security of verifiable credentials in the context of COVID-19 vaccination and test certificates has been questioned. Verifiable credentials have also been subject to usability concerns.

Illustrations

Worked examples

Example 1 — a first encounter with Verifiable credentials

Start with the simplest possible case. Write down what Verifiable credentials claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Verifiable credentials before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Verifiable credentials ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Verifiable credentials

In research: Verifiable credentials appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Verifiable credentials in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Verifiable credentials is common in secondary-school and first-year university syllabi. It links to neighbouring topics World Wide Web Consortium, so understanding it makes those chapters shorter.
In everyday life: Look for Verifiable credentials outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Verifiable credentials in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Verifiable credentials means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Verifiable credentials out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Verifiable credentials in simple terms?

Why does Verifiable credentials matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Verifiable credentials?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Verifiable credentials.