❗ Important! Before you proceed, please read the EUDI Wallet Reference Implementation project description

This library provides a set of classes to manage the transfer of documents in an EUDI ISO 18013-5 Android Wallet.

It defines the interfaces for TransferManager and Transfer classes and provides a standard implementation of the TransferManager.

Currently, the library supports the following devices engagement methods:

• QR
• NFC tag
• Reverse engagement with app link

and the transfer of the documents is done using Bluetooth Low Energy (BLE).

Additionally, Transfer Manager incorporates reader authentication, ensuring the trustworthiness of the verifier (reader) device.

Reader authentication is accomplished by verifying the following:

• Certificate path validation: Verifying the certificate path from the device's certificate to a trusted root certificate
• Certificate's profile validation: Examines the attributes and constraints defined in the certificate profile to ensure that they meet the predefined criteria for a trusted certificate
• CRL validation: Checking the Certificate Revocation List to verify that the certificate has not been revoked or compromised.

The library is written in Kotlin and is available for Android.

The released software is an initial development release version:

• The initial development release is an early endeavor reflecting the efforts of a short timeboxed period, and by no means can be considered as the final product.
• The initial development release may be changed substantially over time, might introduce new features but also may change or remove existing ones, potentially breaking compatibility with your existing code.
• The initial development release is limited in functional scope.
• The initial development release may contain errors or design flaws and other problems that could cause system or other failures and data loss.
• The initial development release has reduced security, privacy, availability, and reliability standards relative to future releases. This could make the software slower, less reliable, or more vulnerable to attacks than mature software.
• The initial development release is not yet comprehensively documented.
• Users of the software must perform sufficient engineering and additional testing in order to properly evaluate their application and determine whether any of the open-sourced components is suitable for use in that application.
• We strongly recommend not putting this version of the software into production use.
• Only the latest version of the software will be supported

• Android 8 (API level 26) or higher

To use snapshot versions, add the following to your project's settings.gradle file:

dependencyResolutionManagement {
    repositories {
        // ...
        maven {
            url = uri("https://central.sonatype.com/repository/maven-snapshots/")
            mavenContent { snapshotsOnly() }
        }
        // ...
    }
}

To include the library in your project, add the following dependencies to your app's build.gradle file.

dependencies {
    implementation "eu.europa.ec.eudi:eudi-lib-android-iso18013-data-transfer:0.10.0"
}

Below is a quick overview of how to use the library.

For source code documentation, see in the docs directory.

The library provides a TransferManager implementation that can be used to present documents using the ISO 18013-5 for proximity presentation and the ISO 18013-7 for remote presentation.

To create a new instance of the TransferManager, you can use the TransferManager.getDefault method.

The following example demonstrates how to create a new instance of the TransferManager

val documentManager: DocumentManager =
    TODO("The document manager to retrieve the requested documents")

val readerTrustStore = ReaderTrustStore.getDefault(
    trustedCertificates = listOf(
        // trustedReaderCertificate1,
        // trustedReaderCertificate2
    )
)

val transferManager = TransferManager.getDefault(
    context = context,
    documentManager = documentManager,
    retrievalMethods = listOf(
        BleRetrievalMethod(
            peripheralServerMode = true,
            centralClientMode = false,
            clearBleCache = true,
        )
    ),
    readerTrustStore = readerTrustStore,
)

The transfer process is event-driven. To receive events, you need to attach a TransferEvent.Listener to the TransferManager.

The available events are:

1. TransferEvent.QrEngagementReady: The QR code is ready to be displayed. Get the QR code from TransferEvent.QrEngagementReady.qrCode.
2. TransferEvent.Connecting: The devices are connecting. Use this event to display a progress indicator.
3. TransferEvent.Connected: the devices are connected.
4. TransferEvent.RequestReceived: A request is received. Get the processed request with the TransferEvent.RequestReceived.processedRequest and the initial raw request as received TransferEvent.RequestReceived.request.
5. TransferEvent.ResponseSent: A response is sent.
6. TransferEvent.Redirect: This event prompts to redirect the user to the given Redirect URI. Get the Redirect URI with TransferEvent.Redirect.redirectUri.
7. TransferEvent.IntentToSend: This event indicates that an intent is ready to be sent. Get the intent with TransferEvent.IntentToSend.intent. This is used mainly for Digital Credential API implementation.
8. TransferEvent.Disconnected: The devices are disconnected.
9. TransferEvent.Error: An error occurred. Get the Throwable error with TransferEvent.Error.error.

The following example demonstrates how to attach a TransferEvent.Listener to the TransferManager. It also demonstrates how to handle the different events.

transferManager.addTransferEventListener { event ->
    when (event) {
        is TransferEvent.QrEngagementReady -> {
            // Qr code is ready to be displayed
            val qrCodeBitmap = event.qrCode.asBitmap(size = 800)
            // or
            val qrCodeView = event.qrCode.asView(context, size = 800)
        }

        TransferEvent.Connecting -> {
            // Informational event that devices are connecting
        }

        TransferEvent.Connected -> {
            // Informational event that the transfer has been connected
        }

        is TransferEvent.RequestReceived -> try {
            // assuming DeviceRequest is the request type
            val processedRequest = event.processedRequest.getOrThrow() as ProcessedDeviceRequest
            // the request has been received and processed

            // the request processing was successful
            // requested documents can be shown in the application
            val requestedDocuments = processedRequest.requestedDocuments
            // ...
            // application must create the DisclosedDocuments object
            val disclosedDocuments = DisclosedDocuments(
                // DisclosedDocument(),
                // DisclosedDocument(),
            )
            // generate the response
            val response = processedRequest.generateResponse(
                disclosedDocuments = disclosedDocuments,
                signatureAlgorithm = Algorithm.ESP256
            ).getOrThrow() as DeviceResponse

            transferManager.sendResponse(response)

        } catch (e: Throwable) {
            // An error occurred
            // handle the error
        }

        TransferEvent.ResponseSent -> {
            // Informational event that the response has been sent
        }
        is TransferEvent.Redirect -> {
            // A redirect is needed. Used mainly for the OpenId4VP implementation
            val redirectUri = event.redirectUri // the redirect URI
        }
        is TransferEvent.IntentToSend -> {
            // An intent is ready to be sent
            // Used mainly for the DCAPI implementation
            val intent = event.intent // the intent to send.
        }
        TransferEvent.Disconnected -> {
            // Informational event that device has been disconnected
        }
        is TransferEvent.Error -> {
            // An error occurred
            val cause = event.error
        }
    }
}

Transfer Manager provides the following methods for enabling device engagement and initiating the transfer:

1. Scanning QR code
2. Reverse engagement using an app link
3. Using NFC .

These engagement methods offer seamless device pairing and data transfer initiation.

With the TransferManager instance created, you can initiate the transfer with QR code by calling the TransferManager.startQrEngagement() method. The method initiates the transfer process and triggers the TransferEvent.QrEngagementReady event when the QR code is ready to be displayed.

To enable ISO 18013-7 REST API functionality, declare to your app's manifest file ( AndroidManifest.xml) an Intent Filter for your MainActivity:

<intent-filter>
    <action android:name="android.intent.action.VIEW" />
    <category android:name="android.intent.category.DEFAULT" />
    <category android:name="android.intent.category.BROWSABLE" />
    <data android:scheme="mdoc" android:host="*" />
</intent-filter>

and set launchMode="singleTask" for this activity.

To initiate the transfer using an app link (reverse engagement), use the TransferManager.startEngagementToApp(Intent) method. The intent contains the mdoc uri for the device engagement.

The example below demonstrates how to initiate the device engagement and transfer.

import androidx.appcompat.app.AppCompatActivity

class MainActivity : AppCompatActivity() {

    // ... rest of activity code

    override fun onResume() {
        super.onResume()
        transferManager.startEngagementToApp(intent)
    }

    override fun onNewIntent(intent: Intent) {
        super.onNewIntent(intent)
        transferManager.startEngagementToApp(intent)
    }
}

To use NFC, you must create a service that extends the abstract NfcEngagementService and override the NfcEngagementService.transferManager property.

For example:

package com.example.myapp

import eu.europa.ec.eudi.iso18013.transfer.engagement.NfcEngagementService

class NfcEngagementServiceImpl : NfcEngagementService() {
    override val transferManager: TransferManager
        get() = TODO("Return the transfer manager here")
}

Then add the service to your application's manifest file, like shown below:

<application>
    <!-- rest of manifest -->
    <service android:exported="true" android:label="@string/nfc_engagement_service_desc"
        android:name="com.example.myapp.NfcEngagementServiceImpl"
        android:permission="android.permission.BIND_NFC_SERVICE">
        <intent-filter>
            <action android:name="android.nfc.action.NDEF_DISCOVERED" />
            <action android:name="android.nfc.cardemulation.action.HOST_APDU_SERVICE" />
        </intent-filter>

        <!-- the following "@xml/nfc_engagement_apdu_service" in meta-data is provided by the library -->
        <meta-data android:name="android.nfc.cardemulation.host_apdu_service"
            android:resource="@xml/nfc_engagement_apdu_service" />
    </service>

</application>

You can enable or disable the NFC device engagement in your app by calling the NfcEngagementService.enable() and NfcEngagementService.disable() methods.

In the example below, the NFC device engagement is enabled when activity is resumed and disabled when the activity is paused.

import androidx.appcompat.app.AppCompatActivity
import eu.europa.ec.eudi.iso18013.transfer.engagement.NfcEngagementService

class MainActivity : AppCompatActivity() {

    override fun onResume() {
        super.onResume()
        NfcEngagementService.enable(this)
    }

    override fun onPause() {
        super.onPause()
        NfcEngagementService.disable(this)
    }
}

Optionally, in the NfcEngagementService.enable() method you can define your class that implements the abstract NfcEngagementService.

For example:

 NfcEngagementService.enable(this, NfcEngagementServiceImpl::class.java)

This way, you can define the NfcEngagementServiceImpl service to be preferred while this activity is in the foreground.

When a request is received, the TransferManager triggers the TransferEvent.RequestReceived. The event contains the processed request and the initial raw request. The processed request is validated and contains the requested documents.

The requested documents can be retrieved by the ProcessedRequest.Success.requestedDocuments property. Each requested document contains the DocumentId that can be used to get the document from the DocumentManager. This will allow the application to display the requested documents to the user.

The ProcessedRequest.Success.generateResponse(DisclosedDocuments, Algorithm?) method is used to generate the response. Each DisclosedDocument in the DisclosedDocuments object must contain the DocumentId and the list of DocItems, that are to be disclosed. There is a possibility that requested document's keys, that are needed to sign the response. In this case, each DisclosedDocument must contain the keyUnlockData property that defines the key unlocking.

Finally, the response is sent back to the verifier with the TransferManager.sendResponse(Response)

The following example demonstrates how to handle the request and send the response.

transferManager.addTransferEventListener { event ->
    when (event) {
        is TransferEvent.RequestReceived -> try {
            // DeviceRequest assumed is received
            val processedRequest = event.processedRequest.getOrThrow() as ProcessedDeviceRequest
            // the request has been received and processed

            // the request processing was successful
            // requested documents can be shown in the application
            val requestedDocuments = processedRequest.requestedDocuments
            // display the requested documents so the user can confirm the disclosure

            // ...

            // Disclosed documents are constructed in ui.
            // If document keys to use for signing response is needed and require unlocking,
            // information about unlocking the keys should be passed to the disclosed document
            // for the corresponding document.
            // Here we use a software key unlock data to unlock the key, for the first requested document.
            val disclosedDocuments = DisclosedDocuments(
                DisclosedDocument(
                    requestedDocuments.first(),
                    keyUnlockData = SoftwareKeyUnlockData(passphrase = "passphrase_passed_from_ui")
                ),
            )
            // generate the response
            val response = processedRequest.generateResponse(
                disclosedDocuments = disclosedDocuments,
                signatureAlgorithm = Algorithm.ESP256
            ).getOrThrow() as DeviceResponse

            transferManager.sendResponse(response)

        } catch (e: Throwable) {
            // An error occurred
            // handle the error
        }

        else -> {
            // ... rest of the events
        }
    }
}

Reader authentication is a critical security component that verifies the authenticity and trustworthiness of the verifier (reader) device before sharing any personal data. It ensures that only legitimate and authorized entities can request and receive sensitive document information.

The library performs three key verification steps:

1. Certificate Path Validation: Validates the complete certificate chain from the reader's certificate up to a trusted root certificate, ensuring a chain of trust is established.

2. Certificate Profile Validation: Examines multiple attributes and constraints defined in the certificate to ensure it meets predefined security criteria, including:

   • Key Usage validation
   • Extended Key Usage validation
   • Validity period verification
   • Critical extensions check
   • Mandatory extensions verification
   • Authority Key Identifier validation
   • Subject Key Identifier validation
   • Common Name verification
   • Signature algorithm verification

3. Certificate Revocation List (CRL) Validation: The library automatically checks if the leaf certificate (reader's certificate) has been revoked by downloading and validating against the CRL distribution points specified in the certificate.

By default, the library provides a standard implementation of the ReaderTrustStore interface through ReaderTrustStoreImpl, which performs all the validations mentioned above:

// Create a default ReaderTrustStore with your trusted certificates
val readerTrustStore = ReaderTrustStore.getDefault(
    trustedCertificates = listOf(
        // List your trusted root certificates here
        trustedRootCertificate1,
        trustedRootCertificate2
    )
)

// Assign the trust store to the TransferManager
transferManager = TransferManager.getDefault(
    context = context,
    documentManager = documentManager,
    retrievalMethods = retrievalMethods,
    readerTrustStore = readerTrustStore
)

For advanced use cases, you can create your own custom implementation of the ReaderTrustStore interface:

class CustomReaderTrustStore(
    private val trustedCertificates: List<X509Certificate>
) : ReaderTrustStore {

    override fun createCertificationTrustPath(chain: List<X509Certificate>): List<X509Certificate>? {
        // Your custom implementation for creating trust path
        // Return the certification path or null if no path can be created
    }

    override fun validateCertificationTrustPath(chainToDocumentSigner: List<X509Certificate>): Boolean {
        // Your custom validation logic
        // Return true if the certification path is valid, false otherwise
    }
}

// Use your custom implementation
val customTrustStore = CustomReaderTrustStore(trustedCertificates)
transferManager.readerTrustStore = customTrustStore

You can also implement custom profile validations by implementing the ProfileValidation interface and providing it to the ReaderTrustStoreImpl:

class CustomProfileValidation : ProfileValidation {
    override fun validate(chain: List<X509Certificate>, trustCA: X509Certificate): Boolean {
        // Your custom validation logic
        return true
    }
}

// Create a ReaderTrustStoreImpl with custom profile validation
val customValidation = CustomProfileValidation()
val readerTrustStore = ReaderTrustStoreImpl(
    trustedCertificates = trustedCertificates,
    profileValidation = customValidation
)

The reader authentication results are accessible through the ReaderAuth object received in the RequestReceived event, allowing you to make decisions based on the authentication status:

is TransferEvent.RequestReceived -> {
    val processedRequest = event.processedRequest.getOrThrow() as ProcessedDeviceRequest
    
    // Access reader authentication information
    val readerAuth = processedRequest.readerAuth
    if (readerAuth != null) {
        val isVerified = readerAuth.isVerified
        val readerCommonName = readerAuth.readerCommonName
        val isTrusted = readerAuth.readerCertificatedIsTrusted
        
        // Make decisions based on authentication status
        if (isVerified && isTrusted) {
            // Proceed with the trusted reader
        } else {
            // Handle untrusted reader scenario
        }
    }
}

We welcome contributions to this project. To ensure that the process is smooth for everyone involved, follow the guidelines found in CONTRIBUTING.md.

See licenses.md for details.

Copyright (c) 2023 European Commission

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.