--- title: "Digital Signature (Two-Step)" canonical_url: "https://www.nutrient.io/guides/android/samples/digital-signature-two-step-kotlin/" md_url: "https://www.nutrient.io/guides/android/samples/digital-signature-two-step-kotlin.md" last_updated: "2026-05-15T19:10:04.916Z" description: "Split digital signing into hash generation and signature embedding for external signing flows." --- # Digital Signature (Two-Step) Split digital signing into hash generation and signature embedding for external signing flows. [Get Started](https://www.nutrient.io/sdk/android/getting-started.md) [All Samples](https://www.nutrient.io/guides/android/samples.md) [Download](https://www.nutrient.io/guides/android/downloads.md) [Launch Demo](https://www.nutrient.io/demo/) --- ```kotlin /* * Copyright © 2020-2026 PSPDFKit GmbH. All rights reserved. * * The PSPDFKit Sample applications are licensed with a modified BSD license. * Please see License for details. This notice may not be removed from this file. */ package com.pspdfkit.catalog.examples.kotlin import android.content.Context import android.net.Uri import android.util.Log import com.pspdfkit.catalog.R import com.pspdfkit.catalog.SdkExample import com.pspdfkit.catalog.SdkExample.Companion.TAG import com.pspdfkit.configuration.activity.PdfActivityConfiguration import com.pspdfkit.document.DocumentSource import com.pspdfkit.document.PdfDocumentLoader import com.pspdfkit.document.providers.AssetDataProvider import com.pspdfkit.signatures.SignerOptions import com.pspdfkit.signatures.SigningManager import com.pspdfkit.signatures.getPrivateKeyEntryFromP12Stream import com.pspdfkit.signatures.getX509Certificates import com.pspdfkit.ui.PdfActivityIntentBuilder import kotlinx.coroutines.CoroutineScope import kotlinx.coroutines.Dispatchers import kotlinx.coroutines.launch import java.io.File import java.io.IOException import java.security.GeneralSecurityException import java.security.KeyStore import java.security.NoSuchAlgorithmException import java.security.PrivateKey import java.security.Signature /** * An example showing the ability to sign a document using a two-step signing process. * */ class TwoStepSigningExample(context: Context) : SdkExample(context, R.string.twoStepSigningExampleTitle, R.string.twoStepSigningExampleDescription) { override val launchRequirements = setOf(SdkExample.LaunchRequirement.DIGITAL_SIGNATURE_TYPE) override fun launchExample(context: Context, configuration: PdfActivityConfiguration.Builder) { val assetName = "Form_example.pdf" val unsignedDocument = PdfDocumentLoader.openDocument(context, DocumentSource(AssetDataProvider(assetName))) val keyEntryWithCertificates = getPrivateKeyEntry(context) val privateKey = keyEntryWithCertificates.privateKey val signatureFormFields = unsignedDocument.documentSignatureInfo.signatureFormFields val outputFile = File(context.filesDir, "signedDocument.pdf") outputFile.delete() // make sure output is deleted from previous runs. /** [SignerOptions] contains all the required configuration for [SigningManager]*/ val signerOptions = SignerOptions.Builder(signatureFormFields[0], Uri.fromFile(outputFile)).setPrivateKey(privateKey).setCertificates(keyEntryWithCertificates.getX509Certificates()).setType(digitalSignatureType) CoroutineScope(Dispatchers.Main).launch { SigningManager.getDataToSign(context, signerOptions.build()).onSuccess { unsignedData -> val signedData = unsignedData.first.signData(privateKey, unsignedData.second.name) SigningManager.embedSignature(context, signerOptions.build(), signedData, unsignedData.first, unsignedData.second).onSuccessEmpty { val intent = PdfActivityIntentBuilder.fromUri(context, Uri.fromFile(outputFile)).configuration(configuration.build()).build() context.startActivity(intent) }.onError { Log.e(TAG, "embedSignature: ${it.localizedMessage}") } }.onError { Log.e(TAG, "getDataToSign: ${it.localizedMessage}") } } } private fun ByteArray.signData(privateKey: PrivateKey, hashAlgorithm: String?): ByteArray = try { // We are using the [Signature] class from java.security package, to sign the byte arrays. // // The signature algorithm can be, among others, the NIST standard DSA, using DSA and SHA-256. // The DSA algorithm using the SHA-256 message digest algorithm can be specified as SHA256withDSA. // In the case of RSA the signing algorithm could be specified as, for example, SHA256withRSA. // The algorithm name must be specified, as there is no default. // // Here 'hashAlgorithm' is SHA256 and 'key.algorithm' is RSA // providing algorithm as SHA256withRSA // for more details visit https://docs.oracle.com/javase/8/docs/api/java/security/Signature.html val algorithm = "${hashAlgorithm}with${privateKey.algorithm}" Signature.getInstance(algorithm).run { initSign(privateKey) // Initialize this object for signing. update(this@signData) // Updates the data to be signed or verified, using the specified array of bytes sign() // Returns the signature bytes of all the data updated } } catch (e: NoSuchAlgorithmException) { throw RuntimeException(e) } /** * Loads the [KeyStore.PrivateKeyEntry] that will be used by our [SigningManager]. */ @Throws(IOException::class, GeneralSecurityException::class) private fun getPrivateKeyEntry(context: Context): KeyStore.PrivateKeyEntry { // Inside a p12 we have both the certificate (or certificate chain to the root CA) and private key used for signing. val keystoreFile = context.assets.open("digital-signatures/ExampleSigner.p12") return getPrivateKeyEntryFromP12Stream(keystoreFile, "test") } } ``` This code sample is an example that illustrates how to use our SDK. Please adapt it to your specific use case. --- ## Related pages - [Application Policy](/guides/android/samples/application-policy-kotlin.md) - [Custom Form Highlight Color](/guides/android/samples/custom-form-highlight-color-java.md) - [Custom Page Templates](/guides/android/samples/custom-page-templates-java.md) - [Digital Signature (Basic)](/guides/android/samples/digital-signature-basic-kotlin.md) - [Disabled Annotation Property](/guides/android/samples/disabled-annotation-property-java.md) - [Image Document](/guides/android/samples/image-document-kotlin.md) - [Compose Image Document](/guides/android/samples/compose-image-document-kotlin.md) - [Inline Multimedia](/guides/android/samples/inline-multimedia-kotlin.md) - [JavaScript Form Filling](/guides/android/samples/javascript-form-filling-kotlin.md) - [Overlay Visibility](/guides/android/samples/overlay-visibility-kotlin.md) - [PdfFragment](/guides/android/samples/pdffragment-kotlin.md) - [Reader View](/guides/android/samples/reader-view-kotlin.md) - [Playground](/guides/android/samples/playground-kotlin.md) - [JavaScript Calculator](/guides/android/samples/javascript-calculator-kotlin.md) - [Text Field Suggestions](/guides/android/samples/text-field-suggestions-kotlin.md) - [Thumbnail Bar Modes](/guides/android/samples/thumbnail-bar-modes-kotlin.md) - [Signature Storage Database](/guides/android/samples/signature-storage-database-kotlin.md) - [Selection Customization](/guides/android/samples/selection-customization-java.md) - [Password Protected PDF](/guides/android/samples/password-protected-pdf-kotlin.md) - [Scientific Paper](/guides/android/samples/scientific-paper-kotlin.md) - [Try Instant](/guides/android/samples/try-instant-kotlin.md) - [Merge Documents](/guides/android/samples/merge-documents-kotlin.md) - [Annotation Rendering](/guides/android/samples/annotation-rendering-kotlin.md) - [Custom Data Provider](/guides/android/samples/custom-data-provider-kotlin.md) - [Annotations with Transparency](/guides/android/samples/annotations-with-transparency-kotlin.md) - [Annotation Flags](/guides/android/samples/annotation-flags-kotlin.md) - [AI Assistant (Multiple Documents, ViewPager)](/guides/android/samples/ai-assistant-multiple-documents-viewpager-kotlin.md) - [Custom Sharing Menu](/guides/android/samples/custom-sharing-menu-java.md) - [Add LTV to Existing Signature](/guides/android/samples/add-ltv-to-existing-signature-kotlin.md) - [Custom Toolbar Grouping](/guides/android/samples/custom-toolbar-grouping-java.md) - [Custom Layout](/guides/android/samples/custom-layout-kotlin.md) - [Custom ActionBar Actions](/guides/android/samples/custom-actionbar-actions-kotlin.md) - [Custom Activity Toolbars](/guides/android/samples/custom-activity-toolbars-java.md) - [Custom Note Hinter](/guides/android/samples/custom-note-hinter-kotlin.md) - [Custom Main Toolbar](/guides/android/samples/custom-main-toolbar-kotlin.md) - [Annotation Configuration](/guides/android/samples/annotation-configuration-kotlin.md) - [Annotation Selection Styling](/guides/android/samples/annotation-selection-styling-kotlin.md) - [Custom Search UI (Compose)](/guides/android/samples/custom-search-ui-compose-kotlin.md) - [Document Switcher](/guides/android/samples/document-switcher-java.md) - [File Annotation Creation](/guides/android/samples/file-annotation-creation-kotlin.md) - [Dynamic Pages on Scroll](/guides/android/samples/dynamic-pages-on-scroll-kotlin.md) - [Custom Activity Form Editing](/guides/android/samples/custom-activity-form-editing-java.md) - [Custom Stamp Annotations](/guides/android/samples/custom-stamp-annotations-java.md) - [Custom Outline Provider](/guides/android/samples/custom-outline-provider-kotlin.md) - [Compose Navigation](/guides/android/samples/compose-navigation-kotlin.md) - [Fragment Runtime Configuration](/guides/android/samples/fragment-runtime-configuration-kotlin.md) - [Annotation Overlay](/guides/android/samples/annotation-overlay-java.md) - [Instant Document JSON](/guides/android/samples/instant-document-json-kotlin.md) - [DocumentView Composable](/guides/android/samples/documentview-composable-kotlin.md) - 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