src.android.security.keystore.AttestationUtils Maven / Gradle / Ivy
/*
* 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 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
*
* Key Attestation for the format of the certificate extension.
*
* 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.
*
* 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;
}
}