212 lines
8.7 KiB
Java
212 lines
8.7 KiB
Java
/*
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* Copyright (C) 2017 The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package android.security.keystore;
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import android.Manifest;
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import android.annotation.NonNull;
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import android.annotation.RequiresPermission;
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import android.annotation.SystemApi;
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import android.content.Context;
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import android.security.keymaster.KeymasterCertificateChain;
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import java.io.ByteArrayInputStream;
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import java.io.ByteArrayOutputStream;
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import java.security.KeyPairGenerator;
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import java.security.KeyStore;
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import java.security.ProviderException;
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import java.security.SecureRandom;
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import java.security.cert.Certificate;
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import java.security.cert.CertificateFactory;
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import java.security.cert.X509Certificate;
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import java.security.spec.ECGenParameterSpec;
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import java.util.Arrays;
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import java.util.Collection;
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import java.util.Random;
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/**
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* Utilities for attesting the device's hardware identifiers.
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*
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* @hide
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*/
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@SystemApi
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public abstract class AttestationUtils {
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private AttestationUtils() {
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}
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/**
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* Specifies that the device should attest its serial number. For use with
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* {@link #attestDeviceIds}.
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*
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* @see #attestDeviceIds
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*/
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public static final int ID_TYPE_SERIAL = 1;
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/**
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* Specifies that the device should attest its IMEIs. For use with {@link #attestDeviceIds}.
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*
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* @see #attestDeviceIds
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*/
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public static final int ID_TYPE_IMEI = 2;
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/**
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* Specifies that the device should attest its MEIDs. For use with {@link #attestDeviceIds}.
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*
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* @see #attestDeviceIds
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*/
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public static final int ID_TYPE_MEID = 3;
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/**
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* Specifies that the device should sign the attestation record using its device-unique
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* attestation certificate. For use with {@link #attestDeviceIds}.
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*
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* @see #attestDeviceIds
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*/
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public static final int USE_INDIVIDUAL_ATTESTATION = 4;
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/**
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* Creates an array of X509Certificates from the provided KeymasterCertificateChain.
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*
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* @hide Only called by the DevicePolicyManager.
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*/
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@NonNull public static X509Certificate[] parseCertificateChain(
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final KeymasterCertificateChain kmChain) throws
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KeyAttestationException {
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// Extract certificate chain.
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final Collection<byte[]> rawChain = kmChain.getCertificates();
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if (rawChain.size() < 2) {
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throw new KeyAttestationException("Attestation certificate chain contained "
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+ rawChain.size() + " entries. At least two are required.");
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}
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final ByteArrayOutputStream concatenatedRawChain = new ByteArrayOutputStream();
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try {
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for (final byte[] cert : rawChain) {
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concatenatedRawChain.write(cert);
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}
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return CertificateFactory.getInstance("X.509").generateCertificates(
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new ByteArrayInputStream(concatenatedRawChain.toByteArray()))
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.toArray(new X509Certificate[0]);
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} catch (Exception e) {
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throw new KeyAttestationException("Unable to construct certificate chain", e);
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}
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}
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/**
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* Performs attestation of the device's identifiers. This method returns a certificate chain
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* whose first element contains the requested device identifiers in an extension. The device's
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* manufacturer, model, brand, device and product are always also included in the attestation.
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* If the device supports attestation in secure hardware, the chain will be rooted at a
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* trustworthy CA key. Otherwise, the chain will be rooted at an untrusted certificate. See
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* <a href="https://developer.android.com/training/articles/security-key-attestation.html">
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* Key Attestation</a> for the format of the certificate extension.
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* <p>
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* Attestation will only be successful when all of the following are true:
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* 1) The device has been set up to support device identifier attestation at the factory.
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* 2) The user has not permanently disabled device identifier attestation.
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* 3) You have permission to access the device identifiers you are requesting attestation for.
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* <p>
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* For privacy reasons, you cannot distinguish between (1) and (2). If attestation is
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* unsuccessful, the device may not support it in general or the user may have permanently
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* disabled it.
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*
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* @param context the context to use for retrieving device identifiers.
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* @param idTypes the types of device identifiers to attest.
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* @param attestationChallenge a blob to include in the certificate alongside the device
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* identifiers.
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*
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* @return a certificate chain containing the requested device identifiers in the first element
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*
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* @exception SecurityException if you are not permitted to obtain an attestation of the
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* device's identifiers.
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* @exception DeviceIdAttestationException if the attestation operation fails.
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*/
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@RequiresPermission(Manifest.permission.READ_PRIVILEGED_PHONE_STATE)
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@NonNull public static X509Certificate[] attestDeviceIds(Context context,
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@NonNull int[] idTypes, @NonNull byte[] attestationChallenge) throws
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DeviceIdAttestationException {
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if (attestationChallenge == null) {
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throw new NullPointerException("Missing attestation challenge");
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}
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if (idTypes == null) {
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throw new NullPointerException("Missing id types");
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}
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String keystoreAlias = generateRandomAlias();
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KeyGenParameterSpec.Builder builder =
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new KeyGenParameterSpec.Builder(keystoreAlias, KeyProperties.PURPOSE_SIGN)
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.setAlgorithmParameterSpec(new ECGenParameterSpec("secp256r1"))
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.setDigests(KeyProperties.DIGEST_SHA256)
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.setAttestationChallenge(attestationChallenge);
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if (idTypes != null) {
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builder.setAttestationIds(idTypes);
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builder.setDevicePropertiesAttestationIncluded(true);
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}
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try {
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KeyPairGenerator keyPairGenerator = KeyPairGenerator.getInstance(
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KeyProperties.KEY_ALGORITHM_EC, "AndroidKeyStore");
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keyPairGenerator.initialize(builder.build());
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keyPairGenerator.generateKeyPair();
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KeyStore keyStore = KeyStore.getInstance("AndroidKeyStore");
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keyStore.load(null);
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Certificate[] certs = keyStore.getCertificateChain(keystoreAlias);
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X509Certificate[] certificateChain =
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Arrays.copyOf(certs, certs.length, X509Certificate[].class);
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keyStore.deleteEntry(keystoreAlias);
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return certificateChain;
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} catch (SecurityException e) {
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throw e;
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} catch (Exception e) {
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// If a DeviceIdAttestationException was previously wrapped with some other type,
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// let's throw the original exception instead of wrapping it yet again.
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if (e.getCause() instanceof DeviceIdAttestationException) {
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throw (DeviceIdAttestationException) e.getCause();
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}
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// Illegal argument errors are wrapped up by a ProviderException. Catch those so that
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// we can unwrap them into a more meaningful exception type for the caller.
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if (e instanceof ProviderException
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&& e.getCause() instanceof IllegalArgumentException) {
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throw (IllegalArgumentException) e.getCause();
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}
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throw new DeviceIdAttestationException("Unable to perform attestation", e);
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}
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}
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private static String generateRandomAlias() {
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Random random = new SecureRandom();
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StringBuilder builder = new StringBuilder();
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// Pick random uppercase letters, A-Z. 20 of them gives us ~94 bits of entropy, which
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// should prevent any conflicts with app-selected aliases, even for very unlucky users.
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for (int i = 0; i < 20; ++i) {
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builder.append(random.nextInt(26) + 'A');
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}
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return builder.toString();
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}
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/**
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* Returns true if the attestation chain provided is a valid key attestation chain.
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* @hide
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*/
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public static boolean isChainValid(KeymasterCertificateChain chain) {
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return chain != null && chain.getCertificates().size() >= 2;
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}
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}
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