This document is a work in progress draft. Last updated at 5 Aug 2020.
Self-sovereign identity is user- and device-centric where an individual or organization or device is able to own its own identity attributes without relying on third-party service providers. Decentralized Identifiers (DIDs) are a new type of identifier for verifiable 'self-sovereign' digital identity for individuals, organizations and things. DIDs have the following important properties:
- Decentralized: DIDs are designed to function without a central registration authority. DIDs are registered in blockchain or other decentralized network.
- Cryptographically Verifiable: DIDs are designed to be associated with cryptographic keys and the entities controlling the DID can use those keys to prove ownership.
- Non-Reassignable: DIDs should be permanent, persistent, and non-reassignable.
- Resolvable: DIDs are made useful through resolution.
This document provides specification of how DID works within IoTeX Network. Our DID design allows each manufacture or entity to have its own namespace, which stores and manages DIDs through a self-managed DID contract. A self-managed contract could have customized business logic to adapt the application's needs but has to implement the SelfManagedDID interface, defined as follows:
interface SelfManagedDID {
function createDID(string id, bytes32 hash, string uri) public returns (string);
function deleteDID(string did) public;
function updateHash(string did, bytes32 hash) public;
function updateURI(string did, string uri) public;
function getHash(string did) public view returns (bytes32);
function getURI(string did) public view returns (string);
}
The following part of this document specifies the IoTeX implementation of the SelfManagedDID interface with DID Method [did:io].
We use the iotex to be our method name and a formal DID using this method need begin with following prefix: did:io . Furthermore, all the characters in the prefix need to be in lowercase. The string after prefix is the unique IoTeX account address of the registered user/device.
Every user or device needs to register its own DID by uploading its UUID under a namespace, DID document hash, and DID document URI. Then a unique idstring is created as follows:
- Construct the
iotexmethod prefix, i.e.did:io. - Append the UUID (IoTeX account address) to the prefix. The UUID must match caller's address.
- The provided DID document hash and URI would be stored in the contract along the unique
idstring.
The DID structure looks like follows:
struct DID {
bool exist;
bytes32 hash;
string uri;
}
An example IoTeX DID:
did:io:0x5576E95935366Ebd2637D9171E4C92e60598be10
IoTeX DID contract implements the functionality of DID registrations. It associates every IoTeX account with a unique dencentralized identifier and a corresponding DID document. Every IoTeX account can only register a DID for itself. It is required that the registerer provides the DID document URI where its document can be accessed and the current document hash that represents the initial state of the document. Here is a draft DID registry implementation:
// For reference only and subject to change
string constant didPrefix = "did:io:";
struct DID {
bool exist;
bytes32 hash;
string uri;
}
mapping(string => DID) dids;
function createDID(string id, bytes32 hash, string uri) public returns (string) {
if (bytes(id).length > 0) {
require(compareStrings(id, addrToString(msg.sender)), "id does not match creator");
}
string memory resultDID = generateDIDString();
require(!dids[resultDID].exist, "did already exists");
dids[resultDID] = DID(true, hash, uri);
return resultDID;
}
function generateDIDString() private view returns (string) {
return string(abi.encodePacked(didPrefix, addrToString(msg.sender)));
}
An example of registration:
createDID("0x5576E95935366Ebd2637D9171E4C92e60598be10", "8806157fdcbcea265623576fa72d88568db3f9ca8b36bddfe3755ae80457eaf5", "user:password@tcp(example_connection_string:3306)/")
Note that id argument is optional because the contract will use the caller's address anyway. Once a DID is registered, the provided DID document hash and URI would be stored in the contract along the unique DID string.
IoTeX clients can query a DID's current hash and URI given a DID string whether they own the DID or not. Here is a draft DID hash/URI read implementation:
// For reference only and subject to change
function getHash(string did) public view returns (bytes32) {
require(dids[did].exist, "did does not exist");
return dids[did].hash;
}
function getURI(string did) public view returns (string) {
require(dids[did].exist, "did does not exist");
return dids[did].uri;
}
Whenever a DID document is modified, the document hash will change and need to be updated in the DID contract. If a user moves the document to a new storage location, the document URI also needs to be updated in the DID contract. Every device can only update its own document associated with the DID created by itself. Here is a draft DID hash/URI update implementation:
// For reference only and subject to change
modifier onlyDIDOwner(string didInput) {
string memory didString = generateDIDString();
if (bytes(didInput).length > 0) {
require(compareStrings(didInput, didString), "caller does not own the given did");
}
require(dids[didString].exist, "caller is not a did owner");
_;
}
function updateHash(string did, bytes32 hash) public onlyDIDOwner(did) {
dids[generateDIDString()].hash = hash;
}
function updateURI(string did, string uri) public onlyDIDOwner(did) {
dids[generateDIDString()].uri = uri;
}
Similar to the case of DID registration, did argument is optional for the update functions as well because the contract would use caller's address to derive the DID string.
A registered DID can be deactivated anytime as long as the caller's address matches the address within the DID string. Once a DID is deactivated, the metadata of the corresponding document cannot be updated. Here is a draft DID hash/URI delete implementation:
// For reference only and subject to change
function deleteDID(string did) public onlyDIDOwner(did) {
dids[generateDIDString()].exist = false;
}
Similar to previous cases, the contract checks the permission to ensure that only the DID creator can deactivate its own DID.
IoTeX DID document is a JSON-LD document containing six, optional components:
- The DID that points to the DID Document, identified by the key id
- A list of public keys identified by the key publickey
- List of protocols for authentication control of the DID and delegated capabilities identified by the key authentication
- A set of service endpoints that allow discovery of way to interact with the entity, identified by the key service
- A timestamp indicates when the DID Document was created and updated, identified by the key created/updated
- A digital signature for verifying the integrity of DID Document, identified by the key proof
Here is a draft IoTeX DID document example:
{
"@context": "https://w3id.org/did/v1",
"id": "did:io:0x88C36867cffB66197812a9385A038cc6Dd75244b",
"publicKey": [{
"id": "did:io:0x5576E95935366Ebd2637D9171E4C92e60598be10#keys-1",
"type": "RsaVerificationKey2018",
"controller": "did:io:0x56d0B5eD3D525332F00C9BC938f93598ab16AAA7",
"publicKeyPem": "-----BEGIN PUBLIC KEY...END PUBLIC KEY-----\r\n" }],
"authentication": [{
"type": "RsaSignatureAuthentication2018",
"publicKey": "did:io:0x5576E95935366Ebd2637D9171E4C92e60598be10#keys-1" }],
"service": [{
"id": "did:io:0x88C36867cffB66197812a9385A038cc6Dd75244b;exam_svc",
"type": "ExampleService",
"serviceEndpoint": "https://example.com/endpoint/8377464" }],
"created": "2018-02-08T16:03:00Z",
"proof": {
"type": "LinkedDataSignature2015",
"created": "2018-02-08T16:02:20Z",
"creator": "did:io:0x5576E95935366Ebd2637D9171E4C92e60598be10#keys-1",
"signatureValue": "QNB13Y7Q9...1tzjn4w=="
}
}
Verifiable claims are statements made by an entity about a 'subject' whose authorship can be cryptographically verified. They can be combined with DID documents to provide trusted service. IoTeX verifiable credentials include the following features:
- Claims are used to create verifiable credentials by issuers.
- Verifiable credentials are decentralized and contextual.
- Credential issuers decide on which claims are contained in the credentials.
- Verifiers make their own trust decisions about which credentials to accept.
- Verifiers do not need to contact issuers to perform verification.
- Credential holders are free to choose which credentials to carry and what information to disclose.
Here is a draft IoTeX verifiable credentials example:
{
"@context": "https://w3id.org/credentials/v1",
"id": "did:io:0xb36A1D1778f9D5E5816682c2cC0d16C65828a6b4/credentials/1",
"type": ["Credential", "NameCredential"],
"issuer": "did:io:0x669d00D4191fB397c780212EB81B439F5Ec9967d",
"issued": "2019-09-01",
"claim": {
"id": "did:io:0x669d00D4191fB397c780212EB81B439F5Ec9967d",
"name": "John Doe",
"address": "..."
},
"proof": {
"type": "RsaSignature2018",
"created": "2017-06-18T21:19:10Z",
"creator": "did:io:0xb36A1D1778f9D5E5816682c2cC0d16C65828a6b4#key-1",
"nonce": "c0ae1c8e-c7e7-469f-b252-86e6a0e7387e",
"signatureValue": "BavEll0/I1zpYw8XNi1bgVg/sCneO4Jugez
8RwDg/+MCRVpjOboDoe4SxxKjkCOvKiCHGDvc4krqi6Z1n0
UfqzxGfmatCuFibcC1wpsPRdW+gGsutPTLzvueMWmFhw
YmfIFpbBu95t501+rSLHIEuujM/+PXr9Cky6Ed+W3JT24=
}
}
The IoTeX DID method covers both people and devices and the following security issues are considered:
The ownership of DIDs is solely based on the knowledge of private keys. Hence the secure storage of private keys is critical. To minimize the risk of private key compromise, using security hardware for key storage is highly recommended. Furthermore, in the case that private key is lost or stolen, an identifier recovery mechanism needs to be in place for enabling a legitimate entity to regain control of the identifier.
A malicious service provider might collect credentials of people and devices with the purpose of impersonating other legitimate entities to gain access for certain services. This issue can be addressed by service providers conducting a challenge-response process with the request entities, thereby verifying that a DID is associated with the request entity.
The IoTeX DID method allows people and devices to store the DID documents and credentials in the storage of their choices. The integrity of this information is ensured by the IoTeX blockchain.
An attacker might launch the Denial of Service (DoS) attacks to prevent access of certain DID documents and/or credentials. To mitigate this issue, DID owners may deploy data redundancy countermeasures by storing multiple copies of DID documents and/or credentials in different storage locations.
The IoTeX DIDs method is implemented by smart contracts on the IoTeX blockchain. Those contracts will go through stringent audits and tests to mitigate the potential security risks.
The private/public key pair used in IoTeX DID method is based on elliptic curve cryptosystems (ECC). The future occurrence of powerful quantum computers will render ECC insecure. Under such a circumstance, a key updating mechanism is needed to generate a new key pair based on the post-quantum cryptographic algorithm selected by the National Institute of Standards and Technology (NIST) for replacing the old one.
The IoTeX DID method involves privacy protection for people and devices and the following privacy issues are considered:
When a person shares his/her personal information with a service provider, the service provider might leak the data to third parties without users’ consent. This issue can be minimized by only sharing the necessary data during the interaction with the service provider rather than exposing the full credential. Advanced cryptographic techniques such as zero-knowledge proofs might be employed to address this issue under certain circumstances.
Since IoTeX DIDs are managed by smart contracts and all the interactions with the smart contracts are recorded on the IoTeX blockchain. By analyzing the transactions on the blockchain, attackers might be able to review the interaction patterns among people or between people and devices. This issue can be minimized by constantly altering the DIDs of people and devices for different interactions according to a predefined policy.
- Decentralized Identifiers (DIDs) v0.13 https://w3c-ccg.github.io/did-spec
- Verifiable Claims https://www.w3.org/TR/verifiable-claims-data-model
- RFC3552 https://tools.ietf.org/html/rfc3552
- RFC6973 https://tools.ietf.org/html/rfc6973