| /* |
| * 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.content.Context; |
| import android.security.keymaster.KeymasterCertificateChain; |
| |
| import java.io.ByteArrayInputStream; |
| import java.io.ByteArrayOutputStream; |
| import java.security.KeyPairGenerator; |
| import java.security.KeyStore; |
| import java.security.ProviderException; |
| import java.security.SecureRandom; |
| import java.security.cert.Certificate; |
| import java.security.cert.CertificateFactory; |
| import java.security.cert.X509Certificate; |
| import java.security.spec.ECGenParameterSpec; |
| import java.util.Arrays; |
| import java.util.Collection; |
| import java.util.Random; |
| |
| /** |
| * Utilities for attesting the device's hardware identifiers. |
| * |
| * @hide |
| */ |
| @SystemApi |
| 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; |
| |
| /** |
| * Specifies that the device should sign the attestation record using its device-unique |
| * attestation certificate. For use with {@link #attestDeviceIds}. |
| * |
| * @see #attestDeviceIds |
| */ |
| public static final int USE_INDIVIDUAL_ATTESTATION = 4; |
| |
| /** |
| * 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); |
| } |
| } |
| |
| /** |
| * 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 { |
| if (attestationChallenge == null) { |
| throw new NullPointerException("Missing attestation challenge"); |
| } |
| if (idTypes == null) { |
| throw new NullPointerException("Missing id types"); |
| } |
| |
| String keystoreAlias = generateRandomAlias(); |
| KeyGenParameterSpec.Builder builder = |
| new KeyGenParameterSpec.Builder(keystoreAlias, KeyProperties.PURPOSE_SIGN) |
| .setAlgorithmParameterSpec(new ECGenParameterSpec("secp256r1")) |
| .setDigests(KeyProperties.DIGEST_SHA256) |
| .setAttestationChallenge(attestationChallenge); |
| |
| if (idTypes != null) { |
| builder.setAttestationIds(idTypes); |
| builder.setDevicePropertiesAttestationIncluded(true); |
| } |
| |
| try { |
| KeyPairGenerator keyPairGenerator = KeyPairGenerator.getInstance( |
| KeyProperties.KEY_ALGORITHM_EC, "AndroidKeyStore"); |
| keyPairGenerator.initialize(builder.build()); |
| keyPairGenerator.generateKeyPair(); |
| |
| KeyStore keyStore = KeyStore.getInstance("AndroidKeyStore"); |
| keyStore.load(null); |
| |
| Certificate[] certs = keyStore.getCertificateChain(keystoreAlias); |
| X509Certificate[] certificateChain = |
| Arrays.copyOf(certs, certs.length, X509Certificate[].class); |
| |
| keyStore.deleteEntry(keystoreAlias); |
| |
| return certificateChain; |
| } catch (SecurityException e) { |
| throw e; |
| } catch (Exception e) { |
| // If a DeviceIdAttestationException was previously wrapped with some other type, |
| // let's throw the original exception instead of wrapping it yet again. |
| if (e.getCause() instanceof DeviceIdAttestationException) { |
| throw (DeviceIdAttestationException) e.getCause(); |
| } |
| // Illegal argument errors are wrapped up by a ProviderException. Catch those so that |
| // we can unwrap them into a more meaningful exception type for the caller. |
| if (e instanceof ProviderException |
| && e.getCause() instanceof IllegalArgumentException) { |
| throw (IllegalArgumentException) e.getCause(); |
| } |
| throw new DeviceIdAttestationException("Unable to perform attestation", e); |
| } |
| } |
| |
| private static String generateRandomAlias() { |
| Random random = new SecureRandom(); |
| StringBuilder builder = new StringBuilder(); |
| // Pick random uppercase letters, A-Z. 20 of them gives us ~94 bits of entropy, which |
| // should prevent any conflicts with app-selected aliases, even for very unlucky users. |
| for (int i = 0; i < 20; ++i) { |
| builder.append(random.nextInt(26) + 'A'); |
| } |
| return builder.toString(); |
| } |
| |
| /** |
| * 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; |
| } |
| } |