jsonld-signatures

An implementation of the Linked Data Signatures specification for JSON-LD. This software works in all modern browsers as well as node.js via npm.

Introduction

A Linked Data Signature proof is created (or verified) by specifying a signature suite and a proof purpose.

The signature suite performs the cryptographic operation required to sign (or verify) a digital signature and includes information in a proof such as the verificationMethod identifier (aka creator) and the date the proof was created (aka created).

The proof purpose indicates why the proof was created and what its intended use is. This information can also be used to make sure that the verificationMethod was authorized for the stated purpose in the proof. Using a proof purpose helps to encourage people to authorize certain cryptographic keys (verification methods) for explicit purposes rather than granting them ambient authority. This approach can help prevent people from accidentally signing documents for reasons they did not intend.

This library provides base classes for signature suites and proof purposes so that custom extensions can be written. It also provides some commonly used signature suites and proof purposes.

This library also supports legacy signature suites such as GraphSignature2012, and LinkedDataSignature2015. These signature suites must be used with a PublicKeyProofPurpose instance as the proof purpose as they were created before extensible proof purposes were possible.

During verification, the key and key controller information must be discovered. This library allows for the key and key controller information to be looked up via a documentLoader or it can be provided directly to the API via the signature suite or proof purpose, respectively.

This library's default documentLoader is very strict for security and content integrity purposes. It will only load locally available copies of the context documents that define the terms it uses internally. Any attempt to load any other documents (including other contexts) will throw an error. If other documents such as verification methods (e.g., public key documents), cannot be provided directly to the API and thus need to be loaded, a custom document loader must be passed. For the sake of clarity, the default document loader will only load locally available copies of the following documents:

• https://w3id.org/security/v1
• https://w3id.org/security/v2

If you require other documents to be loaded then you will need to provide a documentLoader that can provide them. jsonld.js provides both a node and browser documentLoader you can use, however, depending on your use case, you may increase security by using a custom documentLoader that is similarly strict and will only load a subset of documents that is constrained by some technical, security, or business rules.

Install with npm:

npm install jsonld-signatures

In Node.js, include the library like this:

const jsigs = require('jsonld-signatures');

In a browser environment, include jsonld, forge, and dist/jsonld-signatures.min.js via script tag or other mechanism.

Examples

Signing and verifying a simple assertion:

// to generate the next two lines, run the following command:
//
// openssl genrsa -out key.pem; cat key.pem; 
// openssl rsa -in key.pem -pubout -out pubkey.pem;
// cat pubkey.pem; rm key.pem pubkey.pem
//
// for an example of how to specify these keys, look at [key-example]:
const publicKeyPem = "-----BEGIN PUBLIC KEY-----\r\n...";
const privateKeyPem = "-----BEGIN PRIVATE KEY-----\r\n...";

// specify the public key object
const publicKey = {
  '@context': jsigs.SECURITY_CONTEXT_URL,
  type: 'RsaVerificationKey2018',
  id: 'https://example.com/i/alice/keys/1',
  controller: 'https://example.com/i/alice',
  publicKeyPem
};

// specify the public key controller object
const controller = {
  '@context': jsigs.SECURITY_CONTEXT_URL,
  id: 'https://example.com/i/alice',
  publicKey: [publicKey],
  // this authorizes this key to be used for making assertions
  assertionMethod: [publicKey.id]
};

// create the JSON-LD document that should be signed
const doc = {
  '@context': {
    schema: 'http://schema.org/',
    name: 'schema:name',
    homepage: 'schema:url',
    image: 'schema:image'
  },
  name: 'Manu Sporny',
  homepage: 'https://manu.sporny.org/',
  image: 'https://manu.sporny.org/images/manu.png'
};

// sign the document as a simple assertion
const {RsaSignature2018} = jsigs.suites;
const {AssertionProofPurpose} = jsigs.purposes;
const {RSAKeyPair} = require('crypto-ld');
const {documentLoaders} = require('jsonld');

const key = new RSAKeyPair({...publicKey, privateKeyPem});
const signed = await jsigs.sign(doc, {
  suite: new RsaSignature2018({key}),
  purpose: new AssertionProofPurpose()
});

console.log('Signed document:', signed);
// we will need the documentLoader to verify the controller
const {node: documentLoader} = documentLoaders;

// verify the signed document
const result = await jsigs.verify(signed, {
  documentLoader,
  suite: new RsaSignature2018(key),
  purpose: new AssertionProofPurpose({controller})
});
if(result.verified) {
  console.log('Signature verified.');
} else {
  console.log('Signature verification error:', result.error);
}

Signing and verifying a document to authenticate to a website:

const publicKeyBase58 = 'GycSSui454dpYRKiFdsQ5uaE8Gy3ac6dSMPcAoQsk8yq';
const privateKeyBase58 = '3Mmk4UzTRJTEtxaKk61LxtgUxAa2Dg36jF6Vog...SSiF';

// specify the public key object
const publicKey = {
  '@context': jsigs.SECURITY_CONTEXT_URL,
  type: 'Ed25519VerificationKey2018',
  id: 'https://example.com/i/alice/keys/2',
  controller: 'https://example.com/i/alice',
  publicKeyBase58
};

// specify the public key controller object
const controller = {
  '@context': jsigs.SECURITY_CONTEXT_URL,
  id: 'https://example.com/i/alice',
  publicKey: [publicKey],
  // this authorizes this key to be used for authenticating
  authentication: [publicKey.id]
};

// create the JSON-LD document that should be signed
const doc = {
  '@context': {
    schema: 'http://schema.org/',
    action: 'schema:action'
  },
  action: 'AuthenticateMe'
};

// sign the document for the purpose of authentication
const {Ed25519Signature2018} = jsigs.suites;
const {AuthenticationProofPurpose} = jsigs.purposes;
const {Ed25519KeyPair} = require('crypto-ld');
const {documentLoaders} = require('jsonld');

const signed = await jsigs.sign(doc, {
  suite: new Ed25519Signature2018({
    verificationMethod: publicKey.id,
    key: new Ed25519KeyPair({privateKeyBase58})
  }),
  purpose: new AuthenticationProofPurpose({
    challenge: 'abc',
    domain: 'example.com'
  })
});

console.log('Signed document:', signed);
// we will need the documentLoader to verify the controller
const {node: documentLoader} = documentLoaders;

// verify the signed document
const result = await jsigs.verify(signed, {
  documentLoader,
  suite: new Ed25519Signature2018({
    key: new Ed25519KeyPair(publicKey)
  }),
  purpose: new AuthenticationProofPurpose({
    controller,
    challenge: 'abc',
    domain: 'example.com'
  })
});
if(result.verified) {
  console.log('Signature verified.');
} else {
  console.log('Signature verification error:', result.error);
}

Node.js Native Canonize Bindings

Specialized use cases may wish to use the native canonize bindings. This mode can be enabled by setting the useNativeCanonize option to true. See the jsonld.js notes on this feature and note you should benchmark performance before using it.

Commercial Support

Commercial support for this library is available upon request from Digital Bazaar: [email protected]

Source

The source code for the JavaScript implementation of the JSON-LD Signatures API is available at:

https://github.com/digitalbazaar/jsonld-signatures

Tests

This library includes a sample testing utility which may be used to verify that changes to the processor maintain the correct output.

To run the sample tests you will need to get the test suite files by cloning the jsonld-signatures repository hosted on GitHub.

https://github.com/digitalbazaar/jsonld-signatures/

Run the Node.js tests using the following command:

npm run test

Run browser tests using ChromeHeadless using the following command:

npm run test-karma

Run browser tests using a selection of browsers using the following command:

npm run test-karma -- --browsers Firefox,Chrome,ChromeHeadless

Code coverage of node tests can be generated in coverage/:

npm run coverage