Decentralized Identifiers: Verifiable Credentials and Presentations, the easy guide
This is the fourth post on an educational series about Self-Sovereign Identity and Decentralized Identifiers.
Are you done reading our previous posts about decentralized identifiers and personal information and claims? Then let’s move on to the final two elements of the core data model: verifiable credentials and verifiable presentations.
Credentials are a set of one or more claims made by the same entity. They can also include an identifier and metadata to describe the properties of the credential like the issuer, the expiry date and time, a representative image, a public key to use for verification purposes, the revocation mechanism, and so on.
A verifiable credential is a set of tamper-evident claims and metadata that cryptographically proves who issued it. Some examples are employee ID cards, digital birth certificates, and digital educational certificates.
The following image shows a more complete view of a verifiable credential, normally composed of at least two information graphs. The first graph expresses the credential itself, containing credential metadata (in pink) and claims (in yellow). The second graph shows the digital proof (in green), which is usually a digital signature.
Privacy is extremely important when dealing with data. The entities using DIDs will be able to express only the portions of their persona that are appropriate in a given situation. This means that you can choose to show, for example, only the information that shows your are at least 21 years old without giving access to your address or full name when you try to buy an alcoholic drink.
This expression of a subset of one’s persona is called verifiable presentation. One person can have different personas, for example their professional persona, their online gaming persona, their family persona, or an incognito persona.
A verifiable presentation expresses data from one or more verifiable credentials and it’s put in a way that the authorship of the data is verifiable. The information in a presentation is usually about the same subject, but issued by multiple issuers.
Put it simple, if credentials are directly presented, they become a presentation.
The next figure gives a good example of a verifiable presentation which normally is composed of at least four information graphs. The first graph shows the presentation itself, containing presentation metadata (in purple). The verifiable presentation property in the graph points to one or more verifiable credential which in turn contains credential metadata (in pink) and claims (in yellow). The third graph expresses the credential graph proof (in green), which is normally a digital signature. The fourth graph shows the presentation graph proof (in blue), which is also normally a digital signature.
After all these concepts have been understood we are now ready to explain what an ID Hub is and how it can help us keep our identity and information safe. We’ll share all these details on our next post so don’t miss it!
The fifth post in this series is about ID Hub. Let us know what you think and what other identity-related topics we should cover.