README

PE-JS DIF Presentation Exchange Type/JavaScript Library

Active Development

IMPORTANT: This software still is in early development stage. As such you should expect breaking changes in APIs, we expect to keep that to a minimum though.

Background

The PE-JS Library is a general use presentation exchange library that implements the functionality described in the DIF Presentation Exchange v1.0.0 specification. It is written in Typescript and can be compiled to any target JavaScript version.

Sphereon's PE Library is useful for both verifier systems and holders (e.g. wallets) and can be used in client side browsers and mobile applications as well as on server side technology such as REST APIs (e.g. built with NodeJS). It allows anyone to add DIF Presentation Exchange logic to their existing wallets, agents and/or verifiers, without making any further assumptions about the technologies used in their products.

The presentation exchange operates generally as follows; The verifier creates a Presentation Definition asking for credentials from the holder. The definition for the credentials is sent to the holder, who returns a presentation as a response. Now the verifier will verify the presentation by checking the signature and other accompanying proofs.

The presentation exchange will ensure that the model used by the verifier, can be interpreted by the holder. It then ensures that the correct parts from the holders credentials are used to create the presentation. The PE contains all the logic to interpret the models, therefore removing the need for the verifier and holder to align their specific models.

The data objects (models) used in PE-JS are generated from Sphereon's DIF PE OpenAPI Spec component. The code for the component can be seen at PE-OpenAPI github repository. This allows the generation of the objects in many languages and frameworks consistently by configuring the maven plugin.

The PE Library supports the following actions:

Creating a presentation definition / request
Validating a presentation definition / conforming to the specification
Creating a Presentation
Creating a Verifiable Presentation using a callback function
Validating a presentation (submission) when received
Input evaluations: Verification of presentation submissions conforming to the presentation definition
Utilities: to build and use different models compliant with the DIF Presentation Exchange v1.0.0 specification.

Stateful storage, signature support or credential management should be implemented in separate libraries/ modules that make use of the underlying DIF Presentation Exchange implementation. By keeping these separate, the library will stay platform agnostic and lean with regards to dependencies.

For PE-JS Users

The library can be installed direction from npmjs via:

# install via yarn
  yarn add @sphereon/pe-js

# install via npm
  npm install @sphereon/pe-js

The core functionality of the DIF Presentation Exchange can be outlined as follows:

Input Evaluation
Credential Query
Presentation and Verifiable Presentation creation
Utilities

Input Evaluation

Input evaluation is the primary mechanism by which a verifier determines whether a presentation submission from a holder matches the requested presentation definition from the request.

  import pejs from '@sphereon/pe-js';

const presentationDefinition = {
  "id": "32f54163-7166-48f1-93d8-ff217bdb0653",
  "input_descriptors": [
    {
      "id": "wa_driver_license",
      "name": "Washington State Business License",
      "purpose": "We can only allow licensed Washington State business representatives into the WA Business Conference",
      "schema": [{
        "uri": "https://licenses.example.com/business-license.json"
      }]
    }
  ]
};

const verifiablePresentation = {
  '@context': [
    "https://www.w3.org/2018/credentials/v1",
    "https://identity.foundation/presentation-exchange/submission/v1"
  ],
  type: [
    "VerifiablePresentation",
    "PresentationSubmission"
  ],
  presentation_submission: { ... },
  verifiableCredential: [...],
  proof: { ... }
}

const { value, warnings, errors } = pejs.evaluate(presentationDefinition, verifiablePresentation);

Credential Query

A credential query allows holders to filter their set of credentials for matches to a given presentation definition.

  import pejs from '@sphereon/pe-js';

// Definition from verifier request
const presentationDefinition = {
  ...
};

// Example for loading credentials
const credentials = await secureStore.getCredentials();

// Find matching credentials
const srMatches = pejs.selectFrom(presentationDefinition, credentials, holderDid);

// An example that selects the first 'count' credentials from
// the matches. in a real scenario, the user has to select which 
// credentials to use. PE-JS did the first filtering, 
// but there still could be multiple credentials satisfying a presentation definition
const selectedCredentials = srMatches.map(
  ({ matches, count }) => matches.slice(0, count)
).flat();

Presentation creation (non verifiable)

To create a Presentation without Proof (for Proofs, see Verifiable Presentation below) you have to pass in the Presentation Definition, selected Verifiable Credentials and an optional holder (DID). The result will be a Verifiable Presentation, without proofs, so actually a Presentation. It also contains the presentation submission data that the verifier can use.

It is left up to you to sign the Presentation and adding the proof and make it a truly Verifiable Presentation. There are different libraries that allow you to do this. You can also use the callback integration mentioned in the next chapter for this.

  import { pejs, Presentation } from '@sphereon/pe-js';

// Construct presentation from selected credentials
const presentation: Presentation = pejs.presentationFrom(presentationDefinition, selectedCredentials, holderDID);
/** presentation object:
 *
 *   {
 *     "@context": [
 *       "https://www.w3.org/2018/credentials/v1",
 *       "https://identity.foundation/presentation-exchange/submission/v1"
 *     ],
 *     "type": [
 *       "VerifiablePresentation",
 *       "PresentationSubmission"
 *     ],
 *     presentation_submission: presentationSubmission,
 *     verifiableCredential: selectedCredentials
 *   };
 */
// Presentation would need to be signed and sent to verifier

Verifiable Presentation with callback

NOTE: PE-JS does not support the creation of signatures by itself. That has to do with the fact that we didn't want to rely on all kinds of signature suites and libraries. PE-JS has minimal dependencies currently, so that it can be used in all kinds of scenarios.

How did we solve this? We have created a callback mechanism, allowing you to create a callback function that gets all input allowing you to use your library of choice to create the signature. The callback needs to accept a PresentationSignCallBackParams object.

The method verifiablePresentationFrom accepts the presentation definition and selected Verifiable Credentials as the first two arguments, just like the presentationFrom method. Next it accepts the callback function as argument and a PresentationSignOptions object as last argument. The sign callback params, allow you to control the signature process. You will have access in the callback to these params as well.

Before calling your callback function a few things happen. First of all, just like the presentationFrom method, it will evaluate whether the supplied credentials conform to the supplied presentation definition. Then it creates a presentation, just like presentationFrom. This presentation is provided for your convenience and can be used in your callback for simple use cases. In more elaborate cases, like for instance with more complex signature suites and/or selective disclosure, you will probably not use the Presentation directly and make use of other arguments passed into the callback, like the EvaluationResults, PresentationSubmission and Partial<Proof>.

The proofOptions and signatureOptions, allow you to populate proof values directly. in which case the Partial<Proof> will have all fields filled to just add it as a proof to the presentation in your callback. This does mean you would have to create the Presentation first and sign that, which means you probably have no use for the callback. If you do not provide these values, the Partial<Proof>, will still be populated without the proofValue and jws, based upon your options.

Presentation Sign Options

The options accepted by the verifiablePresentationFrom are:

interface PresentationSignOptions {
  /**
   * The optional holder of the presentation
   */
  holder?: string;

  /**
   * Proof options
   */
  proofOptions?: ProofOptions;

  /**
   * The signature options
   */
  signatureOptions?: SignatureOptions;
}

interface ProofOptions {
  /**
   * The signature type. For instance RsaSignature2018
   */
  type?: ProofType | string;

  /**
   * Type supports selective disclosure?
   */
  typeSupportsSelectiveDisclosure?: boolean;

  /**
   * A challenge protecting against replay attacks
   */
  challenge?: string;

  /**
   * A domain protecting against replay attacks
   */
  domain?: string;

  /**
   * The purpose of this proof, for instance assertionMethod or authentication, see https://www.w3.org/TR/vc-data-model/#proofs-signatures-0
   */
  proofPurpose?: ProofPurpose | string;

  /**
   * The ISO8601 date-time string for creation. You can update the Proof value later in the callback. If not supplied the current date/time will be used
   */
  created?: string;

  /**
   * Similar to challenge. A nonce to protect against replay attacks, used in some ZKP proofs
   */
  nonce?: string;
}


interface SignatureOptions {
  /**
   * The private key
   */
  privateKey?: string;

  /**
   * Key encoding
   */
  keyEncoding?: KeyEncoding;

  /**
   * The verification method value
   */
  verificationMethod?: string;

  /**
   * Can be used if you want to provide the Json-ld proof value directly without relying on the callback function generating it
   */
  proofValue?: string; // One of any number of valid representations of proof values

  /**
   * Can be used if you want to provide the JSW proof value directly without relying on the callback function generating it
   */
  jws?: string; // JWS based proof
}

These options are available in your callback function by accessing the options field in the PresentationSignCallBackParams.

Callback params object

The callback params gets supplied as the single argument to your callback function. It contains the Presentation, a partial 'Proof' typically missing the proofValue/jws signature. It also contains the initially supplied Verifiable Credentials and Presentation Definition as well as your supplied options.

If contains the Presentation Submission object, which is also found in the presentation. You can use this to create your own Presentation object if you want. Lastly it contains the evaluation results, which includes the mappings and logs about the evaluation.

You can either choose to use the Presentation and partial Proof together with the options, or in more elaborate use cases opt to use the PresentationSubmission, EvaluationResults and the options for instance.

export interface PresentationSignCallBackParams {

  /**
   * The originally supplied presentation sign options
   */
  options: PresentationSignOptions;

  /**
   * The presentation definition
   */
  presentationDefinition: PresentationDefinition;

  /**
   * The selected credentials to include in the eventual VP as determined by PE-JS and/or user
   */
  selectedCredentials: VerifiableCredential[];

  /**
   * The presentation object created from the definition and verifiable credentials.
   * Can be used directly or in more complex situations can be discarded by using the definition, credentials, proof options, submission and evaluation results
   */
  presentation: Presentation;

  /**
   * A partial proof value the callback can use to complete. If proofValue or JWS was supplied the proof could be complete already
   */
  proof: Partial<Proof>;

  /**
   * The presentation submission data, which can also be found in the presentation itself
   */
  presentationSubmission: PresentationSubmission;

  /**
   * The evaluation results, which the callback function could use to create a VP using the proof(s) using the supplied credentials
   */
  evaluationResults: EvaluationResults;
}

Simple example of the callback function

A simple use case using your library of choice for non-selective disclosure using an ed25519 key and signature.

import {
  pejs,
  Proof,
  ProofPurpose,
  ProofType,
  VerifiablePresentation,
  PresentationSignOptions,
  KeyEncoding
} from '@sphereon/pe-js';

const params: PresentationSignOptions = {
  holder: 'did:example:1234....',
  proofOptions: {
    type: ProofType.Ed25519Signature2018,
    proofPurpose: ProofPurpose.assertionMethod,
  },
  signatureOptions: {
    verificationMethod: 'did:example:"1234......#key',
    keyEncoding: KeyEncoding.Base58,
    privateKey: 'base58 (key encoding type) key here',
  }
}

const vp = pejs.verifiablePresentationFrom(presentationDefinition, selectedCredentials, simpleSignedProofCallback, params);

function simpleSignedProofCallback(callBackParams: PresentationSignCallBackParams): VerifiablePresentation {
  // Prereq is properly filled out `proofOptions` and `signatureOptions`, together with a `proofValue` or `jws` value.
  // And thus a generated signature
  const { presentation, proof, options } = callBackParams; // The created partial proof and presentation, as well as original supplied options
  const { signatureOptions, proofOptions } = options; // extract the orignially supploed signature and proof Options
  const privateKeyBase58 = signatureOptions.privateKey; // Please check keyEncoding from signatureOptions first!

  /**
   * Proof looks like this:
   * {
   *    type: 'Ed25519Signature2018',
   *    created: '2021-12-01T20:10:45.000Z',
   *    proofPurpose: 'assertionMethod',
   *    verificationMethod: 'did:example:"1234......#key',
   *    .....
   * }
   */

    // Just an example. Obviously your lib will have a different method signature
  const vp = myVPSignLibrary(presentation, { ...proof, privateKeyBase58 });

  return vp;
}

Utilities

In addition to the core functionality above, the underlying validation methods are exposed as low-level helper functions.

import pejs from '@sphereon/pe-js';

const presentationDefinition = {
  ...
};

const { warnings: pdWarnings, errors: pdErrors } = pejs.validateDefinition(presentationDefinition);

const presentationSubmission = {
  ...
};

const { warnings: psWarnings, errors: psErrors } = pejs.validateSubmission(presentationSubmission);

API

Evaluate

evaluate(presentationDefinition, verifiablePresentation)

Description

Evaluates whether a presentation submission meets the requested presentation definition Since this method will be used both before and after creating a VerifiablePresentation, we accept both signed and unsigned version of a presentation here.

Parameters

name	type	description
`presentationDefinition`	`PresentationDefinition`	the presentation definition that initiated the request from the verifier
`presentation`	`Presentation`	the Presentation object containing the required credentials and a `presentation_submission` object mapping back to the presentation definition

Return value

If evaluation is successful, value will be a non-null PresentationSubmission mapping the submitted credentials to the requested inputs.

interface EvaluationResults {
  value?: PresentationSubmission;
  warnings?: string[];
  errors?: Error[];
  verifiableCredential: VerifiableCredential[];
}

SelectFrom

selectFrom(presentationDefinition, credentials, holderDids)

Description

Gathers the matching credentials that fit a given presentation definition

Parameters

name	type	description
`presentationDefinition`	`PresentationDefinition`	the presentation definition that initiated the request from the verifier
`credentials`	`VerifiableCredential[]`	the array of verifiable credentials to select from
`holderDids`	`string[]`	the holder's dids. this can be found in VerifiablePresentation's holder property note that a wallet can have many holderDids retrieved from different places

Return value

If the selection was successful or partially successful, the matches array will consist of SubmissionRequirementMatch object(s), representing the matching credentials for each SubmissionRequirement in the presentationDefinition input parameter.
If the selection was not successful, the errors array will consist of Checked object(s), representing what has failed in your selection process.

import { Status } from './ConstraintUtils';

interface SelectResults {
  errors?: Checked[];
  matches?: SubmissionRequirementMatch[];
  /**
   * This is the parameter that pejs library user should look into to determine what to do next
   * Status can have three values:
   *  1. INFO: everything is fine, you can call `presentationFrom` after this method
   *  2. WARN: method was called with more credentials than required.
   *       To enhance credential holder's privacy it is recommended to select credentials which are absolutely required.
   *  3. Error: the credentials you've sent didn't satisfy the requirement defined presentationDefinition object
   */
  areRequiredCredentialsPresent: Status;
  /**
   * All matched/selectable credentials
   */
  verifiableCredential?: VerifiableCredential[];
  /**
   * Following are indexes of the verifiableCredentials passed to the selectFrom method that have been selected.
   */
  vcIndexes?: number[];
  warnings?: Checked[];
}

interface SubmissionRequirementMatch {
  name?: string;
  rule: Rules;
  min?: number;
  count?: number;
  max?: number;
  vc_path: string[];
  from?: string[];
  from_nested?: SubmissionRequirementMatch[]; // VerifiableCredential Address
}

PresentationFrom

presentationFrom(presentationDefinition, selectedCredentials, holderDID)

Description

Creates the corresponding Presentation Submission object to be included in the Verifiable Presentation response, which maps the submitted credentials to the requested inputs in the presentationDefinition input parameter.

Parameters

name	type	description
`presentationDefinition`	`PresentationDefinition`	the presentation definition that initiated the request from the verifier
`selectedCredentials`	`VerifiableCredential[]`	the array of verifiable credentials that meet the submission requirements in the presentation definition
`holderDid`	`string`	the holder's DID. This can be found in VerifiablePresentation's holder property note that a wallet can have many holderDIDs retrieved from different places

Return value

If the selected credentials successfully match the submission requirements in the presentation definition, the return value will be a non-null PresentationSubmission

interface PresentationSubmission {
  id?: string;
  definition_id: string;
  descriptor_map: Descriptor[]
}

Validation

validateDefinition(objToValidate)

validateSubmission(objToValidate)

Description

A validation utility function for PresentationDefinition and PresentationSubmission objects.

Parameters

name	type	description
`objToValidate`	`PresentationDefinition \| PresentationSubmission`	the presentation definition or presentation definition to be validated

Return value

The validate method returns a validated results array NonEmptyArray<Checked> , with structure:

interface Checked {
  tag: string;
  status: Status;
  message?: string;
}

status can have following values 'info' | 'warn' | 'error'

Workflow Diagram

Flow diagram

For PE-JS developers

This project has been created using:

yarn version 1.22.5
node version 12.22.1

Install

yarn install

Build

yarn build

Test

The test command runs:

eslint
prettier
unit

You can also run only a single section of these tests, using for example yarn test:unit.

yarn test

Utility scripts

There are several other utility scripts that help with development.

yarn fix - runs eslint --fix as well as prettier to fix code style
yarn cov - generates code coverage report

Glossary

Term	Definition
Credential	A set of one or more claims made by an issuer.
Verifiable Credential	Is a tamper-evident credential that has authorship that can be cryptographically verified. Verifiable credentials can be used to build verifiable presentations, which can also be cryptographically verified. The claims in a credential can be about different subjects.
Presentation Definition	Presentation Definitions are objects that articulate what proofs a Verifier requires.
Holder	Holders are entities that have one or more verifiable credentials in their possession. Holders are also the entities that submit proofs to Verifiers to satisfy the requirements described in a Presentation Definition.
Holder's Did	Unique ID URI string and PKI metadata document format for describing the cryptographic keys and other fundamental PKI values linked to a unique, user-controlled, self-sovereign identifier in holder's wallet
Verifier	Verifiers are entities that define what proofs they require from a Holder (via a Presentation Definition) in order to proceed with an interaction.
Issuer	A role an entity can perform by asserting claims about one or more subjects, creating a verifiable credential from these claims, and transmitting the verifiable credential to a holder.
Presentation	Data derived from one or more verifiable credentials, issued by one or more issuers
Verifiable Presentation	Is a tamper-evident presentation encoded in such a way that authorship of the data can be trusted after a process of cryptographic verification.

Further work:

Implementation of presentation-exchange v2
In the DIF documentation some entries are addressing nested credentials and nested paths these are currently not fully support yet.

Usage no npm install needed!

README

PE-JS DIF Presentation Exchange Type/JavaScript Library

Active Development

Background

The PE Library supports the following actions:

For PE-JS Users

Input Evaluation

Credential Query

Presentation creation (non verifiable)

Verifiable Presentation with callback

Presentation Sign Options

Callback params object

Simple example of the callback function

Utilities

API

Evaluate

Description

Parameters

Return value

SelectFrom

Description

Parameters

Return value

PresentationFrom

Description

Parameters

Return value

Validation

Description

Parameters

Return value

Workflow Diagram

For PE-JS developers

Install

Build

Test

Utility scripts

Glossary

Further work: