Background

The Presentation Exchange (PEX) Library implements the functionality described in the DIF Presentation Exchange specification for both version 1 and 2.

Sphereon's PEX 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 technologies like cryptography, credential representations used in their products.

A Presentation Exchange generally goes as follows; The verifier creates a Presentation Definition asking for credentials from the holder. The Presentation Definition for the credentials is sent to the holder, who returns a Verifiable Presentation containing Presentation Submission data that links the Credentials in the Presentation to the received Definition as a response. The Presentation Submission describes the relationship between the Verifiable Presentation and the Presentation Definition. It can either be part of the Verifiable Presentation or be external, like in OpenID4VC specifications. Now the verifier will verify the Verifiable Presentation by checking the signature and other accompanying proofs as well as ensuring the Submission Data fulfills the requirements from the specification.

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 PEX-library contains all the logic to interpret the models, therefore removing the need for the verifier and holder to align their specific models.

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

WARNING: Please be aware that this library does not support the latest V2 specification!. Support will be added as part of a V3 major version of this library

The PEX Library supports the following actions:

• Creating a presentation definition / request
• Validating a presentation definition / conforming to the specifications v1 and v2
• 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 v2.0.0 specification.
• Support for 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 this library. By keeping these separate, the PEX library will stay platform-agnostic and lean with respect to dependencies.

For PEX Users

The library can be installed directly from npmjs via:

# install via yarn
  yarn add @sphereon/pex

# install via npm
  npm install @sphereon/pex

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

• Verifiers/Agents:

  • Input Evaluation
  • Utilities

• Holders/Wallets:

  • Credential Query
  • Non-Verifiable Presentation creation
  • Verifiable Presentation creation
  • Utilities

Verifier: Create a Presentation Definition object:

Presentation Definitions are objects that articulate what proofs a Verifier requires. These help the Verifier to decide how or whether to interact with a Holder. Presentation Definitions are composed of inputs, which describe the forms and details of the proofs they require, and optional sets of selection rules, to allow Holders flexibility in cases where different types of proofs may satisfy an input requirement. PEX library supports two versions of presentation_definition object. The details of it can be found in @spehereon/pex-models below you can find some tips about querying via a presentation_definition object:

• Using the constraint field:
  • You can use the constraint field for creating your query:

constraints: {
  fields: [
    {
      path: ['$.credentialSubject.role'],
      filter: {
        type: 'string',
        const: 'admin'
      }
    }
  ];
}

• for special cases, like querying fields that start with @ you can use the following syntax:
  • You can use the following syntax, PEX will change it to correct query itself:

path: ['$.@context', '$.vc.@context']

For querying the arrays, right now we don't support the json-schema fully, but we do support the following syntax:

• using [*] like:

{
  fields: [
    {
      path: [
        '$.type.[*]'
      ],
      filter: {
        type: 'string',
        pattern: 'AlumniCredential'
      }
    }
  ]
}

• using .* like:

{
  fields: [
    {
      path: [
        '$.type.*'
      ],
      filter: {
        type: 'string',
        pattern: 'AlumniCredential'
      }
    }
  ]
}

• using type: array and contains keyword. PEX currently doesn't support this syntax fully, but if you don't rely on our versionDiscovery functionality and call the specific version of PEX (PEXv1 or PEXv2) yourself, you can use this syntax as well.

{
  "fields": [
    {
      "path": [
        "$.type"
      ],
      "filter": {
        "type": "array",
        "contains": {
          "enum": [
            "https://example.com/type"
          ]
        }
      }
    }
  ]
}

Verifier: Input Evaluation

Input evaluation is the primary mechanism by which a verifier determines whether a Verifiable Presentation and Presentation Submission from a holder matches the requested presentation definition from the request. Obviously a holder/wallet could also use the method to verify whether its submission would be valid, before contacting the verifier.

import { PEX } from '@sphereon/pex';

const pex: PEX = new PEX();

// Example of Presentation Definition V1 (notice the required schema for V1)
const presentationDefinitionV1 = {
  "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"
      }]
    }
  ]
};

// Example of Presentation Definition V2
const presentationDefinitionV2 = {
  "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"
    }
  ]
};

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

// We are using the PEX class, to automatically detect the definition version. PEXv1 and PEXv2 are also available to use fixed PEX versions
const { value, warnings, errors } = pex.evaluatePresentation(presentationDefinitionV2, verifiablePresentation);

Holder: Credential Query

A credential query allows holders to filter their set of credentials for matches to a given presentation definition. This filters out any non-matching Credentials that are passed in. Please note that multiple credentials could be satisfying the definition.

import { PEX } from '@sphereon/pex';
import { IVerifiableCredential } from "./SSI.types";

const pex: PEX = new PEX();

// Definition from verifier request
const presentationDefinition = {
  ...
};
// Finding out which version presentationDefinition is this:
// The result is either 'v1', 'v2' or an error
// You only have to do this if you want to apply some custom logic. The PEX class uses feature detection on the definition to determine whether it is v1 or v2 internally
const result = PEX.definitionVersionDiscovery(pdSchema);

// Example for loading credentials from your secure storage
const credentials: IVerifiableCredential[] = await secureStore.getCredentials();

// Find matching credentials
const srMatches = pex.selectFrom(presentationDefinition, credentials, { holderDIDs: [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. PEX 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();

Holder: 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 { PEX, IPresentation, PresentationResult } from '@sphereon/pex';

const pex: PEX = new PEX();

// Construct presentation from selected credentials
const presentationResult: PresentationResult = pex.presentationFrom(presentationDefinition, selectedCredentials, { holderDIDs: [holderDID] });
const presentation = presentationResult.presentation
/** 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

Holder: Verifiable Presentation with callback

NOTE: PEX 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. PEX 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 supply 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.

NOTE: 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 VerifiablePresentationFromOpts 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, 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 IPresentation directly and make use of other arguments passed into the callback, like the EvaluationResults, PresentationSubmission and Partial<IProof>.

The proofOptions and signatureOptions, allow you to populate proof values directly. in which case the Partial<IProof> 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 IPresentation first and sign that, which means you probably have no use for the callback. If you do not provide these values, the Partial<IProof>, will still be populated without the proofValue and jws, based upon your options.

Presentation Sign Options

The options accepted by the verifiablePresentationFrom are:

interface VerifiablePresentationFromOpts {
  /**
   * The optional holderDID of the presentation
   */
  holderDID?: string;

  /**
   * The presentation submission data location.
   *
   * Can be External, which means it is only returned and not embedded into the VP,
   * or Presentation, which means it will become part of the VP
   */
  presentationSubmissionLocation?: PresentationSubmissionLocation;

  /**
   * A base presentation payload. Can be used to provide default values. Be aware that any verifiable credential will always be overwritten
   */
  basePresentationPayload?: IPresentation;

  /**
   * IProof 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 IProof 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 IPresentation 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: VerifiablePresentationFromOpts;

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

  /**
   * The selected credentials to include in the eventual VP as determined by PEX and/or user
   */
  selectedCredentials: (IVerifiableCredential | JwtWrappedVerifiableCredential | string)[];

  /**
   * 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: IPresentation;

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

  /**
   * 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 {
  PEX,
  IProof,
  ProofPurpose,
  ProofType,
  IVerifiablePresentation,
  PresentationSignOptions,
  KeyEncoding,
} from '@sphereon/pex';

const pex: PEX = new PEX();

const params: VerifiablePresentationFromOpts = {
  holderDID: '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 = await pex.verifiablePresentationFrom(
  presentationDefinition,
  selectedCredentials,
  simpleSignedProofCallback,
  params
);

function simpleSignedProofCallback(callBackParams: PresentationSignCallBackParams): IVerifiablePresentation {
  // 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!

  /**
   * IProof 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 { PEX } from '@sphereon/pex';

const presentationDefinition = {
  ...
};

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

const presentationSubmission = {
  ...
};

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

API

Evaluate

PEX.evaluatePresentation(presentationDefinition, verifiablePresentation);
PEXv1.evaluatePresentation(presentationDefinition, verifiablePresentation);
PEXv2.evaluatePresentation(presentationDefinition, verifiablePresentation);

Description

These three methods are quite similar. The first One receives a presentation definition object, decides the version based upon feature detection and acts accordingly. The other two are specific to their Presentation Exchange definition version.

For more detailed difference between v1 and v2 please read the From V1 to V2 section.

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 | IPresentation | 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: (IVerifiableCredential | JwtWrappedVerifiableCredential | string)[];
}

SelectFrom

PEX.selectFrom(presentationDefinition, credentials, { holderDIDs });
PEXv1.selectFrom(presentationDefinitionV1, credentials, { holderDIDs });
PEXv2.selectFrom(presentationDefinitionV2, credentials, { holderDIDs });

Description

These three methods are quite similar. The first One receives a presentation definition object, decides the version based upon feature detection and acts accordingly. The other two are specific to their version.

For more detailed difference between v1 and v2 of the spec please read the From V1 to V2 section.

Gathers the matching credentials that fit a given presentation definition. Please note that there could be multiple results fitting the same criteria. This basically only filters out the credentials that do not match the definition. You, or rather the user, typically has to do a final selection.

selectFrom Parameters

| name | type | description | |--------------------------|-------------------------------------------------------------------------|--------------------------------------------------------------------------------------------------------------------------------------------------------------| | presentationDefinition | PresentationDefinition | the presentation definition that initiated the request from the verifier | | credentials | (IVerifiableCredential or JwtWrappedVerifiableCredential or string)[] | 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 the PEX 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 holderDID'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. Do not submit!
   */
  areRequiredCredentialsPresent: Status;
  /**
   * All matched/selectable credentials
   */
  verifiableCredential?: (IVerifiableCredential | JwtWrappedVerifiableCredential | string)[];
  /**
   * 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

PEX.presentationFrom(presentationDefinition, selectedCredentials, { holderDID });
PEXv1.presentationFrom(presentationDefinitionV1, selectedCredentials, { holderDID });
PEXv2.presentationFrom(presentationDefinitionV2, selectedCredentials, { holderDID });

Description

These three methods are quite similar. The first One receives a presentation definition object, decides the version based upon feature detection and acts accordingly. The other two are specific to their version.

**For more detailed difference between v1 and v2 specification please read the From V1 to V2 section **.

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.

presentationFromV1 Parameters

| name | type | description | |--------------------------|-------------------------------------------------------------------------|--------------------------------------------------------------------------------------------------------------------------------------------------------------| | presentationDefinition | PresentationDefinitionV1 | the v1 presentation definition that initiated the request from the verifier | | selectedCredentials | (IVerifiableCredential or JwtWrappedVerifiableCredential or string)[] | 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 IVerifiablePresentation's holder property note that a wallet can have many holderDIDs retrieved from different places |

presentationFromV2 Parameters

| name | type | description | |--------------------------|-------------------------------------------------------------------------|--------------------------------------------------------------------------------------------------------------------------------------------------------------| | presentationDefinition | PresentationDefinitionV2 | the v2 presentation definition that initiated the request from the verifier | | selectedCredentials | (IVerifiableCredential or JwtWrappedVerifiableCredential or string)[] | 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 IVerifiablePresentation'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 'Presentation' containing a PresentationSubmission

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

Validation

PEX.validateDefinition(objToValidate);
PEXv1.validateDefinition(objToValidate);
PEXv2.validateDefinition(objToValidate);

validateSubmission(objToValidate);

Description

A validation utility function for PresentationDefinition and PresentationSubmission objects. If you know the version of your presentation definition you can call version-specific functions. If not you can call the general one (located in PEX) to first determine the version and then validate the presentation definition object against that version's specific rules.

Parameters

| name | type | description | |-----------------|-------------------------------------------------------------------|------------------------------------------------------------------------| | objToValidate | PresentationDefinition | PresentationSubmission | the presentation definition or presentation submission 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'

Definition Version Discovery

PEX.definitionVersionDiscovery(presentationDefinition);

Description

A utility function for PresentationDefinition objects. This method will determine the version of your presentationDefinition object.

Parameters

| name | type | description | |--------------------------|-------------------------------------|---------------------------------------------------------------------| | presentationDefinition | PresentationDefinition | the presentation definition that you need to decide the version for |

Return value

The definitionVersionDiscovery method returns a version or an error, with following structure:

interface DiscoveredVersion {
  version?: PEVersion;
  error?: string;
}

enum PEVersion {
  v1 = 'v1',
  v2 = 'v2',
}

From V1 to V2

The following changes has been made in the v2 version of the Presentation Exchange specification. V1 is still the most predominant version, because it is typically used quite a bite in OpenID4VC scenarios and interop profiles.

1. The required schema has been removed altogether from InputDescriptor properties, because it was confusing and redundant.
2. presentation_definition has another property called frame and if present, its value MUST be a JSON LD Framing Document object. Used for selective disclosure. Although this library does not use it currently, as we can perform it without frames.
3. filter has several more options for filtering:
   • formatMaximum
   • formatMinimum
   • formatExclusiveMaximum
   • formatExclusiveMinimum

As a result we introduced the PEX class to replace the former PEJS class. This class does feature detection on the presentation definition to determine whether it is a v1 or v2 spec. Then it delegates the functionality to the PEXv1 or PEXv2 class respectively. See also: v0.6 Breaking changes

WARNING: Please be aware that this library does not support the latest V2 specification!. Support will be added as part of a V3 major version of this library

Workflow Diagram

The below diagram shows how a typical interaction between a verifier and a wallet looks like. It makes no assumptions about the actual transport (DIDComm, SIOPv2/OIDC4VP, CHAPI, REST)

For PEX developers

This project has been created using:

• yarn version 1.22.5
• node version >= 16

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. PEX accepts Verifiable credential in 3 forms: 1. JSON_LD which is know in our system as IVerifiableCredential, 2. JWT-Wrapped VC which is known in our system as JwtWrappedVerifiableCredential or string which is a valid Verifiable credential jwt | | 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:

This implementation fully supports V1 and Vpartially 2 of the Presentation Exchange specification with the following exception:

• Support for hashlink verification in the schema part of the V1 specification is not fully incorporated as it depends on missing external library support. We generate a warning about the missing verification if we encounter them.
• Support for complete json-schema in pex-models
  • which means if you're relying on our version-discovery feature (with calling general PEX) and sending presentation_definition object with unsupported fields, you'll get an exception. However if you call specific version of PEX (PEXv1 or PEXv2) it will work.
• The V2 implementation does not contain latest V2 changes. These will become available in V3 of this library

Breaking changes

v2.0.0 Argument and result objects changed slightly

In V2 of the library we have done some refactoring on the PEX external interfaces, to make them more uniform.

Optional arguments for all PEX methods are now part of an optional opts Object argument. This allows for cleaner future extensions, and also solves the problem of optional argument order in case multiple optional arguments are needed.

Certain non state related methods part of the PEX/PEXv1/PEXv2 classes have moved to static methods, to make the distinction between state related methods and non-state related methods more clear.

presentationFrom and verifiablePresentationFrom now return a result object instead of directly returning a ( Verifiable) Presentation. Reason is that in certain use cases you will want to have an external Presentation Submission object, like for instance in OpenID4VP.

You can now provide an optional argument where the Presentation Submission object should be located. It will always be returned in the methods, as well as an indication whether it is used externally or embedded into the (Verifiable) Presentation.

The (Verifiable) Presentation object is present in the result object in the presentation resp. verifiablePresentation property.

No more need for _const and _enum models/properties in Presentation Definitions. They are now const and enum (fixed in OpenAPI model generation). The code replaces the previous versions to be sure.

v0.6.0: class and package renamed

As part of introducing Presentation Exchange v1 and v2 feature based detection support to our Presentation Exchange library and not reaching version 1.X yet, we decided to change the name of both the package and the main entry class:

• The package was changed from @sphereon/pe-js to @sphereon/pex
• The main class was changed from PEJS to PEX. The latter class has internal feature detection support on the provided definition, delegating the actual implementation to the new PEXv1 or PEXv2 class internally. If you don't want the automatic feature detection you can also choose to use the PEXv1 and PEXv2 classes directly.

License

This Presentation Exchange library Open Source software released under the Apache 2.0 license.

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