content: /*
   * Copyright (C) 2017 The Android Open Source Project
   *
   * 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.
   */
  
  package android.security.keystore;
  
  import android.Manifest;
  import android.annotation.NonNull;
  import android.annotation.RequiresPermission;
  import android.annotation.SystemApi;
  import android.annotation.TestApi;
  import android.content.Context;
  import android.content.res.Resources;
  import android.os.Build;
  import android.security.KeyStore;
  import android.security.keymaster.KeymasterArguments;
  import android.security.keymaster.KeymasterCertificateChain;
  import android.security.keymaster.KeymasterDefs;
  import android.telephony.TelephonyManager;
  import android.text.TextUtils;
  import android.util.ArraySet;
  
  import java.io.ByteArrayInputStream;
  import java.io.ByteArrayOutputStream;
  import java.nio.charset.StandardCharsets;
  import java.security.cert.CertificateFactory;
  import java.security.cert.X509Certificate;
  import java.util.Collection;
  import java.util.Set;
  
  /**
   * Utilities for attesting the device's hardware identifiers.
   *
   * @hide
   */
  @SystemApi
  @TestApi
  public abstract class AttestationUtils {
      private AttestationUtils() {
      }
  
      /**
       * Specifies that the device should attest its serial number. For use with
       * {@link #attestDeviceIds}.
       *
       * @see #attestDeviceIds
       */
      public static final int ID_TYPE_SERIAL = 1;
  
      /**
       * Specifies that the device should attest its IMEIs. For use with {@link #attestDeviceIds}.
       *
       * @see #attestDeviceIds
       */
      public static final int ID_TYPE_IMEI = 2;
  
      /**
       * Specifies that the device should attest its MEIDs. For use with {@link #attestDeviceIds}.
       *
       * @see #attestDeviceIds
       */
      public static final int ID_TYPE_MEID = 3;
  
      /**
       * Creates an array of X509Certificates from the provided KeymasterCertificateChain.
       *
       * @hide Only called by the DevicePolicyManager.
       */
      @NonNull public static X509Certificate[] parseCertificateChain(
              final KeymasterCertificateChain kmChain) throws
              KeyAttestationException {
          // Extract certificate chain.
          final Collection<byte[]> rawChain = kmChain.getCertificates();
          if (rawChain.size() < 2) {
              throw new KeyAttestationException("Attestation certificate chain contained "
                      + rawChain.size() + " entries. At least two are required.");
          }
          final ByteArrayOutputStream concatenatedRawChain = new ByteArrayOutputStream();
          try {
              for (final byte[] cert : rawChain) {
                  concatenatedRawChain.write(cert);
              }
              return CertificateFactory.getInstance("X.509").generateCertificates(
                      new ByteArrayInputStream(concatenatedRawChain.toByteArray()))
                              .toArray(new X509Certificate[0]);
          } catch (Exception e) {
              throw new KeyAttestationException("Unable to construct certificate chain", e);
          }
      }
  
      @NonNull private static KeymasterArguments prepareAttestationArgumentsForDeviceId(
              Context context, @NonNull int[] idTypes, @NonNull byte[] attestationChallenge) throws
              DeviceIdAttestationException {
          // Verify that device ID attestation types are provided.
          if (idTypes == null) {
              throw new NullPointerException("Missing id types");
          }
  
          return prepareAttestationArguments(context, idTypes, attestationChallenge);
      }
  
      /**
       * Prepares Keymaster Arguments with attestation data.
       * @hide should only be used by KeyChain.
       */
      @NonNull public static KeymasterArguments prepareAttestationArguments(Context context,
              @NonNull int[] idTypes, @NonNull byte[] attestationChallenge) throws
              DeviceIdAttestationException {
          return prepareAttestationArguments(context, idTypes,attestationChallenge, Build.BRAND);
      }
  
      /**
       * Prepares Keymaster Arguments with attestation data for misprovisioned Pixel 2 device.
       * See http://go/keyAttestationFailure and http://b/69471841 for more info.
       * @hide should only be used by KeyChain.
       */
      @NonNull public static KeymasterArguments prepareAttestationArgumentsIfMisprovisioned(
              Context context, @NonNull int[] idTypes, @NonNull byte[] attestationChallenge) throws
              DeviceIdAttestationException {
          Resources resources = context.getResources();
          String misprovisionedBrand = resources.getString(
                  com.android.internal.R.string.config_misprovisionedBrandValue);
          if (!TextUtils.isEmpty(misprovisionedBrand) && !isPotentiallyMisprovisionedDevice(context)){
              return null;
          }
          return prepareAttestationArguments(
                  context, idTypes, attestationChallenge, misprovisionedBrand);
      }
  
      @NonNull private static boolean isPotentiallyMisprovisionedDevice(Context context) {
          Resources resources = context.getResources();
          String misprovisionedModel = resources.getString(
                  com.android.internal.R.string.config_misprovisionedDeviceModel);
          return (Build.MODEL.equals(misprovisionedModel));
      }
  
      @NonNull private static KeymasterArguments prepareAttestationArguments(Context context,
              @NonNull int[] idTypes, @NonNull byte[] attestationChallenge, String brand) throws
              DeviceIdAttestationException {
          // Check method arguments, retrieve requested device IDs and prepare attestation arguments.
          if (attestationChallenge == null) {
              throw new NullPointerException("Missing attestation challenge");
          }
          final KeymasterArguments attestArgs = new KeymasterArguments();
          attestArgs.addBytes(KeymasterDefs.KM_TAG_ATTESTATION_CHALLENGE, attestationChallenge);
          // Return early if the caller did not request any device identifiers to be included in the
          // attestation record.
          if (idTypes == null) {
              return attestArgs;
          }
          final Set<Integer> idTypesSet = new ArraySet<>(idTypes.length);
          for (int idType : idTypes) {
              idTypesSet.add(idType);
          }
          TelephonyManager telephonyService = null;
          if (idTypesSet.contains(ID_TYPE_IMEI) || idTypesSet.contains(ID_TYPE_MEID)) {
              telephonyService = (TelephonyManager) context.getSystemService(
                      Context.TELEPHONY_SERVICE);
              if (telephonyService == null) {
                  throw new DeviceIdAttestationException("Unable to access telephony service");
              }
          }
          for (final Integer idType : idTypesSet) {
              switch (idType) {
                  case ID_TYPE_SERIAL:
                      attestArgs.addBytes(KeymasterDefs.KM_TAG_ATTESTATION_ID_SERIAL,
                              Build.getSerial().getBytes(StandardCharsets.UTF_8));
                      break;
                  case ID_TYPE_IMEI: {
                      final String imei = telephonyService.getImei(0);
                      if (imei == null) {
                          throw new DeviceIdAttestationException("Unable to retrieve IMEI");
                      }
                      attestArgs.addBytes(KeymasterDefs.KM_TAG_ATTESTATION_ID_IMEI,
                              imei.getBytes(StandardCharsets.UTF_8));
                      break;
                  }
                  case ID_TYPE_MEID: {
                      final String meid = telephonyService.getMeid(0);
                      if (meid == null) {
                          throw new DeviceIdAttestationException("Unable to retrieve MEID");
                      }
                      attestArgs.addBytes(KeymasterDefs.KM_TAG_ATTESTATION_ID_MEID,
                              meid.getBytes(StandardCharsets.UTF_8));
                      break;
                  }
                  default:
                      throw new IllegalArgumentException("Unknown device ID type " + idType);
              }
          }
          attestArgs.addBytes(KeymasterDefs.KM_TAG_ATTESTATION_ID_BRAND,
                  brand.getBytes(StandardCharsets.UTF_8));
          attestArgs.addBytes(KeymasterDefs.KM_TAG_ATTESTATION_ID_DEVICE,
                  Build.DEVICE.getBytes(StandardCharsets.UTF_8));
          attestArgs.addBytes(KeymasterDefs.KM_TAG_ATTESTATION_ID_PRODUCT,
                  Build.PRODUCT.getBytes(StandardCharsets.UTF_8));
          attestArgs.addBytes(KeymasterDefs.KM_TAG_ATTESTATION_ID_MANUFACTURER,
                  Build.MANUFACTURER.getBytes(StandardCharsets.UTF_8));
          attestArgs.addBytes(KeymasterDefs.KM_TAG_ATTESTATION_ID_MODEL,
                  Build.MODEL.getBytes(StandardCharsets.UTF_8));
          return attestArgs;
      }
  
      /**
       * Performs attestation of the device's identifiers. This method returns a certificate chain
       * whose first element contains the requested device identifiers in an extension. The device's
       * manufacturer, model, brand, device and product are always also included in the attestation.
       * If the device supports attestation in secure hardware, the chain will be rooted at a
       * trustworthy CA key. Otherwise, the chain will be rooted at an untrusted certificate. See
       * <a href="https://developer.android.com/training/articles/security-key-attestation.html">
       * Key Attestation</a> for the format of the certificate extension.
       * <p>
       * Attestation will only be successful when all of the following are true:
       * 1) The device has been set up to support device identifier attestation at the factory.
       * 2) The user has not permanently disabled device identifier attestation.
       * 3) You have permission to access the device identifiers you are requesting attestation for.
       * <p>
       * For privacy reasons, you cannot distinguish between (1) and (2). If attestation is
       * unsuccessful, the device may not support it in general or the user may have permanently
       * disabled it.
       *
       * @param context the context to use for retrieving device identifiers.
       * @param idTypes the types of device identifiers to attest.
       * @param attestationChallenge a blob to include in the certificate alongside the device
       * identifiers.
       *
       * @return a certificate chain containing the requested device identifiers in the first element
       *
       * @exception SecurityException if you are not permitted to obtain an attestation of the
       * device's identifiers.
       * @exception DeviceIdAttestationException if the attestation operation fails.
       */
      @RequiresPermission(Manifest.permission.READ_PRIVILEGED_PHONE_STATE)
      @NonNull public static X509Certificate[] attestDeviceIds(Context context,
              @NonNull int[] idTypes, @NonNull byte[] attestationChallenge) throws
              DeviceIdAttestationException {
          final KeymasterArguments attestArgs = prepareAttestationArgumentsForDeviceId(
                  context, idTypes, attestationChallenge);
  
          // Perform attestation.
          final KeymasterCertificateChain outChain = new KeymasterCertificateChain();
          final int errorCode = KeyStore.getInstance().attestDeviceIds(attestArgs, outChain);
          if (errorCode != KeyStore.NO_ERROR) {
              throw new DeviceIdAttestationException("Unable to perform attestation",
                      KeyStore.getKeyStoreException(errorCode));
          }
  
          try {
              return parseCertificateChain(outChain);
          } catch (KeyAttestationException e) {
              throw new DeviceIdAttestationException(e.getMessage(), e);
          }
      }
  
      /**
       * Returns true if the attestation chain provided is a valid key attestation chain.
       * @hide
       */
      public static boolean isChainValid(KeymasterCertificateChain chain) {
          return chain != null && chain.getCertificates().size() >= 2;
      }
  }
  