AssetDIDs

KILT DIDs are suitable for those use cases that involve so-called "active" participants, i.e., entities that can act out of their will (a person, an organization, a DAO).

There are classes of entities that represent "passive" participants, i.e., they can be "used" by active participants within a given use case. We define these class of participants assets. As with traditional KILT users, assets also need to be uniquely identified.

This is what an AssetDID, of which KILT is the ideator and initial editor, does. An example of a valid AssetDID is the following: did:asset:eip155:1.erc721:0xb47e3cd837ddf8e4c57f05d70ab865de6e193bbb. This AssetDID refers to the CryptoPunks NFT collection.

AssetDID structure

An AssetDID is a generative identifier, meaning that it does not depend nor rely on any information stored anywhere. Rather, given the asset that needs to be identified, it is always possible to generate its AssetDID (hence the term generative). The reverse is also true: given an AssetDID, it is always possible to dereference it into its building components which, together, uniquely identified a given asset.

AssetDIDs always start with the did:asset prefix, and then contain a chain component (namespace + reference) and an asset component (namespace + reference + identifier).

Chain Namespace and Chain Reference

Together, they identify the (blockchain) network on which the asset lives.

In the case of NFTs, this would represent the blockchain on which the smart contract is deployed. Different deployments of the same network will have the same chain namespace but a different reference. For instance, both the Ethereum mainnet and the Goerli testnet have a chain namespace of eip155, but the former is identified by the reference 1 (being the mainnet), while the Goerli testnet is identified by the reference 5.

A list of Ethereum chain IDs (which are used as reference) can be found on chainlist.org.

Asset Namespace, Asset Reference and Asset Identifier

Similarly to their chain counterparts, asset namespaces are used to distinguish among different asset classes that might live within the same environment. In the case of NFTs for instance, a smart contract could support both ERC20 (fungible) and ERC721 (non-fungible) tokens, hence the namespace is used to distinguish between the two token types.

Each asset namespace defines the semantics and the meaning of asset references and asset identifiers within that namespace. In the example of Ethereum-based NFTs, the asset reference identifies the smart contract address on which the NFT is stored. Hence, the combination of asset namespace + asset reference is sufficient to identify an NFT collection on a given network.

For some assets, for instance NFTs, it is possible to specify an asset identifier, which is used to refer to a single item within the collection. In the example of the CryptoPunks collection above, the AssetDID could be extended with an additional :1005 to now refer to the CryptoPunk piece #1005 rather than to the CryptoPunks collection as a whole.

Credits to OpenSea for the NFT image above.

For a more technical explanation of AssetDIDs, please visit our official specification.