# Create a Device Attestation Certificate (DAC)
<a name="JavaApiCBC-DeviceAttestationCertificate"></a>

This Java sample shows how to use the [BlankEndEntityCertificate\$1CriticalBasicConstraints\$1APIPassthrough/V1](template-definitions.md#BlankEndEntityCertificate_CriticalBasicConstraints_APIPassthrough) template to create a [Matter](https://buildwithmatter.com) Device Attestation Certificate. You must generate a Base64-encoded KeyUsage value and pass it through a CustomExtension.

The example calls the following AWS Private CA API action:
+ [IssueCertificate](https://docs.aws.amazon.com/privateca/latest/APIReference/API_IssueCertificate.html)

If you encounter problems, see [Troubleshoot AWS Private CA Matter-compliant certificate errorsMatter-compliant certificate errors](TroubleshootPcaMatter.md) in the Troubleshooting section.

```
package com.amazonaws.samples.matter;

import com.amazonaws.auth.AWSCredentials;
import com.amazonaws.auth.profile.ProfileCredentialsProvider;
import com.amazonaws.client.builder.AwsClientBuilder;
import com.amazonaws.client.builder.AwsClientBuilder.EndpointConfiguration;
import com.amazonaws.auth.AWSStaticCredentialsProvider;

import java.nio.ByteBuffer;
import java.nio.charset.StandardCharsets;
import java.util.Arrays;
import java.util.Base64;
import java.util.List;
import java.util.Objects;

import com.amazonaws.services.acmpca.AWSACMPCA;
import com.amazonaws.services.acmpca.AWSACMPCAClientBuilder;

import com.amazonaws.services.acmpca.model.ASN1Subject;
import com.amazonaws.services.acmpca.model.ApiPassthrough;
import com.amazonaws.services.acmpca.model.CustomAttribute;
import com.amazonaws.services.acmpca.model.CustomExtension;
import com.amazonaws.services.acmpca.model.Extensions;
import com.amazonaws.services.acmpca.model.IssueCertificateRequest;
import com.amazonaws.services.acmpca.model.IssueCertificateResult;
import com.amazonaws.services.acmpca.model.SigningAlgorithm;
import com.amazonaws.services.acmpca.model.Validity;

import com.amazonaws.AmazonClientException;
import com.amazonaws.services.acmpca.model.LimitExceededException;
import com.amazonaws.services.acmpca.model.ResourceNotFoundException;
import com.amazonaws.services.acmpca.model.InvalidStateException;
import com.amazonaws.services.acmpca.model.InvalidArnException;
import com.amazonaws.services.acmpca.model.InvalidArgsException;
import com.amazonaws.services.acmpca.model.MalformedCSRException;

import org.bouncycastle.asn1.x509.KeyUsage;
import org.bouncycastle.jce.X509KeyUsage;

import lombok.SneakyThrows;

public class IssueDeviceAttestationCertificate {
   public static ByteBuffer stringToByteBuffer(final String string) {
      if (Objects.isNull(string)) {
          return null;
      }
      byte[] bytes = string.getBytes(StandardCharsets.UTF_8);
      return ByteBuffer.wrap(bytes);
   }

   @SneakyThrows
   private static String generateKeyUsageValue() {
      KeyUsage keyUsage = new KeyUsage(X509KeyUsage.digitalSignature);
      byte[] kuBytes = keyUsage.getEncoded();
      return Base64.getEncoder().encodeToString(kuBytes);
   }

   public static void main(String[] args) throws Exception {

      // Retrieve your credentials from the C:\Users\name\.aws\credentials file
      // in Windows or the .aws/credentials file in Linux.
      AWSCredentials credentials = null;
      try {
          credentials = new ProfileCredentialsProvider("default").getCredentials();
      } catch (Exception e) {
          throw new AmazonClientException("Cannot load your credentials from disk", e);
      }

      // Define the endpoint for your sample.
      String endpointRegion = "region";  // Substitute your region here, e.g. "ap-southeast-2"
      String endpointProtocol = "https://acm-pca." + endpointRegion + ".amazonaws.com/";
      EndpointConfiguration endpoint =
          new AwsClientBuilder.EndpointConfiguration(endpointProtocol, endpointRegion);

      // Create a client that you can use to make requests.
      AWSACMPCA client = AWSACMPCAClientBuilder.standard()
          .withEndpointConfiguration(endpoint)
          .withCredentials(new AWSStaticCredentialsProvider(credentials))
          .build();

      // Create a certificate request:
      IssueCertificateRequest req = new IssueCertificateRequest();

      // Set the CA ARN.
      req.withCertificateAuthorityArn("arn:aws:acm-pca:region:123456789012:certificate-authority/12345678-1234-1234-1234-123456789012");

      // Specify the certificate signing request (CSR) for the certificate to be signed and issued.
      String strCSR =
      "-----BEGIN CERTIFICATE REQUEST-----\n" +
      "base64-encoded certificate\n" +
      "-----END CERTIFICATE REQUEST-----\n";
      ByteBuffer csrByteBuffer = stringToByteBuffer(strCSR);
      req.setCsr(csrByteBuffer);

      // Specify the template for the issued certificate.
      req.withTemplateArn("arn:aws:acm-pca:::template/BlankEndEntityCertificate_CriticalBasicConstraints_APIPassthrough/V1");

      // Set the signing algorithm.
      req.withSigningAlgorithm(SigningAlgorithm.SHA256WITHECDSA);

      // Set the validity period for the certificate to be issued.
      Validity validity = new Validity();
      validity.withValue(10L);
      validity.withType("DAYS");
      req.withValidity(validity);

      // Set the idempotency token.
      req.setIdempotencyToken("1234");

      // Define custom attributes
      List<CustomAttribute> customAttributes = Arrays.asList(
         new CustomAttribute()
            .withObjectIdentifier("2.5.4.3")
            .withValue("Matter Test DAC 0001"),
         new CustomAttribute()
            .withObjectIdentifier("1.3.6.1.4.1.37244.2.1")
            .withValue("FFF1"),
         new CustomAttribute()
            .withObjectIdentifier("1.3.6.1.4.1.37244.2.2")
            .withValue("8000")
      );

      // Define a cert subject.
      ASN1Subject subject = new ASN1Subject();
      subject.setCustomAttributes(customAttributes);

      ApiPassthrough apiPassthrough = new ApiPassthrough();
      apiPassthrough.setSubject(subject);

      // Generate Base64 encoded extension value for ExtendedKeyUsage
      String base64EncodedKUValue = generateKeyUsageValue();

      // Generate custom extension
      CustomExtension customKeyUsageExtension = new CustomExtension();
      customKeyUsageExtension.setObjectIdentifier("2.5.29.15"); // KeyUsage Extension OID
      customKeyUsageExtension.setValue(base64EncodedKUValue);
      customKeyUsageExtension.setCritical(true);
      
      Extensions extensions = new Extensions();
      extensions.setCustomExtensions(Arrays.asList(customKeyUsageExtension));
      apiPassthrough.setExtensions(extensions);
      req.setApiPassthrough(apiPassthrough);

      // Issue the certificate.
      IssueCertificateResult result = null;
      try {
         result = client.issueCertificate(req);
      } catch (LimitExceededException ex) {
         throw ex;
      } catch (ResourceNotFoundException ex) {
         throw ex;
      } catch (InvalidStateException ex) {
         throw ex;
      } catch (InvalidArnException ex) {
         throw ex;
      } catch (InvalidArgsException ex) {
         throw ex;
      } catch (MalformedCSRException ex) {
         throw ex;
      }

      // Retrieve and display the certificate ARN.
      String arn = result.getCertificateArn();
      System.out.println(arn);
   }
}
```