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OpenAttestation

OpenAttestation is a framework of attestation and notary for any document types on the blockchain.

With OpenAttestation, you can issue and verify verifiable documents individually or in a batch using:

  • either smart contracts on the Ethereum blockchain

  • or digital signatures without the need to pay for Ethereum transactions

Installation​

To install the OpenAttestation framework on your machine, run the command below:

npm i @govtechsg/open-attestation

Usage​

Wrapping documents​

The wrapDocuments function takes in an array of documents and returns the wrapped batch. Each document must be valid according to the version of the schema used. It computes the merkle root of the batch and appends it to each document. This merkle root can be published on the blockchain and be queried against to prove the provenance of the document issued this way. Alternatively, the merkle root may be signed by the document issuer's private key, which may be cryptographically verified using the issuer's public key or Ethereum account to act as proof of issuance.

Version of the schema​

In future, this function may accept a second optional parameter to specify the version of open-attestation you want to use. Currently, open-attestation will use schema 2.0. See Additional Information for how to use experimental v3.0 documents, which aim to be compatible with the W3C's data model for Verifiable Credentials.

Code example​

The wrapDocument function is almost identical with wrapDocuments, but the first function accepts only one document.

The following code example shows how wrapDocuments works. You can also do some tweaking to apply it on wrapDocument.

import { wrapDocuments } from "@govtechsg/open-attestation";
const document = {
  id: "SERIAL_NUMBER_123",
  $template: {
    name: "CUSTOM_TEMPLATE",
    type: "EMBEDDED_RENDERER",
    url: "https://localhost:3000/renderer",
  },
  issuers: [
    {
      name: "DEMO STORE",
      tokenRegistry: "0x9178F546D3FF57D7A6352bD61B80cCCD46199C2d",
      identityProof: {
        type: "DNS-TXT",
        location: "tradetrust.io",
      },
    },
  ],
  recipient: {
    name: "Recipient Name",
  },
  unknownKey: "unknownValue",
  attachments: [
    {
      filename: "sample.pdf",
      type: "application/pdf",
      data: "BASE64_ENCODED_FILE",
    },
  ],
};

wrappedDocuments = wrapDocuments([document, { ...document, id: "different id" }]); // will ensure document is valid regarding open-attestation 2.0 schema
console.log(wrappedDocuments);

Differences between the two similar functions​

Although wrapDocument and wrapDocuments are almost identical, there are minor differences.

  • The wrapDocuments function returns an array and not an object.
  • Each element in the array is a wrapped document corresponding to the one provided as input.
  • Each element will share the same unique merkleRoot value in every batch wrap instance.
  • Each element has a unique targetHash value.
  • Similar to wrapDocument, every time you run wrapDocuments, it will create unique hashes (in front of every field in the data object).

Signing a document​

The signDocument function takes a wrapped document, as well as a public/private key pair or an Ethers.js Signer. The method will sign the merkle root from the wrapped document, append the signature to the document, and return it. Currently, it supports the signing algorithm below:

  • Secp256k1VerificationKey2018

Example with a public/private key pair​

The following code example of signDocument contains a public/private key pair.

import { signDocument, SUPPORTED_SIGNING_ALGORITHM } from "@govtechsg/open-attestation";
await signDocument(wrappedV2Document, SUPPORTED_SIGNING_ALGORITHM.Secp256k1VerificationKey2018, {
  public: "did:ethr:0xE712878f6E8d5d4F9e87E10DA604F9cB564C9a89#controller",
  private: "0x497c85ed89f1874ba37532d1e33519aba15bd533cdcb90774cc497bfe3cde655",
});

Example with the signer​

The following code example of signDocument contains the signer information.

import { signDocument, SUPPORTED_SIGNING_ALGORITHM } from "@govtechsg/open-attestation";
import { Wallet } from "@ethersproject/wallet";

const wallet = Wallet.fromMnemonic("tourist quality multiply denial diary height funny calm disease buddy speed gold");
const { proof } = await signDocument(
  wrappedDocumentV2,
  SUPPORTED_SIGNING_ALGORITHM.Secp256k1VerificationKey2018,
  wallet
);

Validating the document schema​

The validateSchema function checks that the document conforms to OpenAttestation data structure.

import { validateSchema } from "@govtechsg/open-attestation";
const validatedSchema = validateSchema(wrappedDocument);
console.log(validatedSchema);

Verifying the document signature​

The verifySignature function checks that the signature of the document corresponds to the actual content in the document. In addition, it checks that the target hash (hash of the document content) is part of the set of documents wrapped in the batch using the proofs.

import { verifySignature } from "@govtechsg/open-attestation";
const verified = verifySignature(wrappedDocument);
console.log(verified);

Note: This method does not check against the blockchain or any registry if this document has been published. The merkle root of this document needs to be checked against a publicly accessible document store, which in the case of OpenAttestation is a smart contract on the blockchain.

Retrieving the document data​

The getData function returns the original data stored in the document in a readable format.

import { getData } from "@govtechsg/open-attestation";
const data = getData(wrappedDocument);
console.log(data);

Utils​

A number of utility functions can be found under utils, which check whether a document is a valid OA file that has been wrapped or signed. The diagnose function can also be used for troubleshooting.

import { utils } from "@govtechsg/open-attestation";
utils.isWrappedV3Document(document);

You can replace isWrappedV3Document in the above example with the following values:

  • isWrappedV2Document: This is the type guard for the wrapped V2 document.
  • isSignedWrappedV2Document: This is the type guard for the signed V2 document.
  • isSignedWrappedV3Document: This is the type guard for the signed V3 document.
  • isWrappedV3Document: This is the type guard for the wrapped V3 document.

In addition, the diagnose tool can find out why a document is not a valid OpenAttestation file (wrapped or signed document).

Obfuscating data​

The obfuscateDocument function removes a key-value pair from the document's data section, without causing the file hash to change. You can use this to generate a new document containing a subset of the original data.

const newData = obfuscateDocument(wrappedDocument, "key1");
console.log(newData);

Development​

To run tests, use the following command:

npm run test

vc-test-suite​

You can run vc-test-suite against open-attestation by using the npm run test:vc command. It will:

  • clone https://github.com/w3c/vc-test-suite.git

  • copy the local configuration (vc-test-suite-config.json) into the cloned repository

  • install the latest version of @govtechsg/open-attestation-cli

  • monkey patch open-attestation in @govtechsg/open-attestation-cli

    "Monkey patch" means it will build the current version of the project, which will replace the one installed with @govtechsg/open-attestation-cli.

Local debugging​

If you face a problem with one test and want to debug locally:

  1. Ensure the vc-test-suite folder is available from the root of the project.

    If not, run npm run test:vc first and perform the test again.

  2. Open runVcTest.sh and update install_vc_test_suite=true to install_vc_test_suite=false.

    This line will preserve the vc-test-suite folder untouched.

You can now debug from the vc-test-suite folder the way you need.

Additional information​

  • If you find a bug, have a question, or want to share an idea, reach us at our Github repository.
  • We are currently building a new version of the schema compatible with W3C VC. This is very experimental and whatever is available for V2 documents are also available for V3 documents:
    • OA schema v3
    • Typings: import {v3} from "@govtechsg/open-attestation".
    • Type guard: utils.isWrappedV3Document.
    • Wrapping: __unsafe__use__it__at__your__own__risks__wrapDocument
      • future usage: wrapDocument(document, {version: "open-attestation/3.0"})
    • Example docs in tests/fixtures/v3
  • There are extra utilities available:
    • Refer to the utils component for the full list of utilities.