An attribute is the smallest unit in the IRMA system. It is a small piece of information like a telephone number or birth date that can be independently disclosed.
A credential is a bundle of attributes with a fixed structure and a cryptographic signature to verify its authenticity. During disclosure, the whole credential is disclosed but non-disclosed attributes are cryptographically blacked out without invalidating the signature. This is one of the key benefits of the IRMA system. The structure of credentials is described in a scheme.
You could compare a credential to a class instance in object oriented programming or to a struct instance in C. Its member variables would then be the credential's attributes. The structure of the credential described in the scheme would then be the class or struct definition.
An issuer is an organization that gives out credentials (containing attributes) after some form of verification. The Privacy by Design Foundation issues a few basic credentials but it is expected other organizations will issue their own credentials soon.
A scheme describes all issuers, all credentials, as well as attributes it contains. (Additionally, it contains the IRMA public keys of the issuers against which their attributes can be verified.) An example of a scheme is the Privacy by Design Foundation scheme.
- Disclosure process
An identifier uniquely identifies an attribute type, credential type, issuer, or scheme. Examples are
pbdf.pbdf.ageLimits.over18which is the Over 18 attribute,
pbdf.pbdf.bigwhich is the BIG registration credential, or
pbdf.pbdfwhich is the Privacy by Design Foundation issuer.
- XML source
Each page of this index is an automatically generated human-readable view on an XML file within a scheme. Each page include a link to the XML file from which it was generated.
You can read more about the disclosure process in the protocol description.
For a more comprehensive introduction of these entities and their role in the IRMA infrastructure, see the technical documentation.