DIDs have several ways of supporting multiple authors / devices. The DID Core specification currently defines these properties/features:
- DID controller (
controller). A DID Document can have multiple controllers. It is up to the DID Method how these should work, but I believe the default is independent control, i.e. each listed controller gets full control.
- Also Known As (
alsoKnownAs) - DID Document property. Similar to SSB
- equivalentId and canonicalId - DID Document metadata properties (these exist outside the DID document). Could be used along with
canonicalId are marked in the spec as feature at risk: if they are not sufficiently implemented, they may be removed from the Core specification, as explained in %OgynFTq.... (But even if removed, the features could still be usable and may be registered in the DID Specification Registries).
DIDs could also support multiple authors / devices, in method-specific ways, without relying on specific properties defined in the specification or registered extensions. For example:
- did:web (DID document served over HTTPS): a domain name could have multiple IP addresses with different web servers serving requests for the DID document; or a single server that retrieves the DID document from other devices, or just allows the DID controller to make changes remotely from different devices.
- did:key (DID document deterministically derived from public key in the DID): the private key could simply exist in multiple locations. The DID Document Update operation is not supported, so there is no issue of ordering update events. (although the
signed-ietf-json-patchextension may be used).
- DID Methods based on blockchains rely on the blockchain's consensus mechanism.
Another way would be for a DID Document to contain multiple verification methods. A verification method is typically a public key, for the purpose of authentication, or other purposes (corresponding to verification relationships). A DID document could contain multiple public keys, one for each of the user's devices (for the case where the DID Subject is a person with multiple devices). There is also a proposal for a type of verification method,
VerifiableCondition, that could be used to combine verification methods in "m-of-n" configurations.