We rate this blog post as very relevant, because it gives a thorough overview of the definitions related to Decentralized Identity.

Definitions related to Decentralized Identity

(discussed in the Decentralized Identity: The Ultimate Guide 2022 https://blog.dock.io/decentralized-identity/ .)

Self-Sovereign Identity (SSI)

Self-Sovereign Identity (SSI) is used interchangeably with the term Decentralized Identity.

SSI consists of the following four parts :

• Blockchain.

• Verifiable Credentials: a cryptographically secure, digital version of credentials (paper or digital) that users can present to possible verifiers. This digital version should comply with Verifiable Credentials Data Model v1.1.

• Decentralized Identifiers (DIDs): an identifier that is cryptographically verifiable and is created and managed by the user.

• Decentralized Identity Wallet: an application that allows users to create their DIDs and store their verifiable credentials.

Centralized Identity Management

Every user creates a username and a password for each service.

Disadvantage: Single point of failure for data breaches. Some examples of such incidents are described in this paper: “Digital Identities and Verifiable Credentials''.

Federated Identity Management

Users can access multiple applications by using a single set of credentials. An example is when the user signs in to multiple applications using its Google or Facebook account.

Disadvantage: There is no unlinkability : if multiple applications collude could possibly detect if the same user has registered to all of them using the same account.

Decentralized Identity

Users store the data in their digital wallets and they have the option to choose when and which part of this data they want to reveal.

Standards For Decentralised Identity

• World Wide Web Consortium (W3C)

• Internet Engineering Task Force (IETF)

• Decentralized Identity Foundation (DIF)

Decentralized Identity on the Blockchain

There is an issuer, a holder, and a verifier.

• Both the issuer and the holder hold a DID that is possibly stored on the blockchain and it may be associated with a public key (this depends on the generation method). Some examples of DID methods can be found also here EBSI DID Method.

• The issuer signs a claim for the holder (e.g the issuer is a university and signs a degree) using its private key. This will constitute a verifiable credential.

• The holder holds this credential in a digital wallet and presents it to the verifier.

• The verifier checks which DID and public key corresponds to the issuer and verifies the signature.

What can be stored on the blockchain:

• All the DIDs

• Public Keys

• Proof of credentials (in case the issuer wants to timestamp a credential)

• Revocation Registry (in case the issuer wants to have the option to retrieve the certificates that it has issued).

DIDs in Dock

Example : did:dock:GhkJkjhertFlkiid

• Globally unique identifiers that are associated with one or multiple private/public key pairs.

• They do not contain any private information

• The owner can cryptographically prove that it owns this DID.

• They can enable secure and private communication between two parties.

• Each person can create multiple DIDs for different purposes. Note: many applications (e.g Decentralised Identity in Tezos) consider this as an advantage and they do not seem to take into account the Sybil problem at this point, because it offers pairwise privacy (there is no correlation of identities among several web pages or services).

Layers in the decentralized Identity Ecosystem

Layer 1 Standards: They ensure interoperability, standardization, portability

Layer 2 Infrastructure: Interaction between applications and with the verifiable data registries (e.g blockchain).

Layer 3 Identifiers and VC: authentication of DIDs and the presentation of the credentials.

Layer 4 apps, wallets, products: Use cases

References

• Decentralized Identity: The Ultimate Guide 2022 https://blog.dock.io/decentralized-identity/

• Verifiable Credentials Data Model v1.1 : W3C recommendation https://www.w3.org/TR/vc-data-model/

• Decentralized Identity Foundation (DIF) https://identity.foundation/

• Internet Engineering Task Force (IETF) https://www.ietf.org/

• Sedlmeir, J., Smethurst, R., Rieger, A. et al. Digital Identities and Verifiable Credentials. Bus Inf Syst Eng 63, 603–613 (2021). https://doi.org/10.1007/s12599-021-00722-y

• Zero-knowledge credentials with deferred revocation checks https://github.com/decentralized-identity/snark-credentials/blob/master/whitepaper.pdf

• EBSI DID Method: https://ec.europa.eu/digital-building-blocks/wikis/display/EBSIDOC/EBSI+DID+Method

• D. Maram et al., "CanDID: Can-Do Decentralized Identity with Legacy Compatibility, Sybil-Resistance, and Accountability," 2021 IEEE Symposium on Security and Privacy (SP) , 2021, pp. 1348-1366, doi: 10.1109/SP40001.2021.00038.

• Decentralized Identity with the Tezos DID Method https://sprucesystems.medium.com/decentralized-identity-with-the-tezos-did-method-d9cf6676dd64

• World Wide Web Consortium https://decentralized-id.com/web-standards/w3c/