chromium/net/X509Util.java

// Copyright 2012 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

package org.chromium.net;

import android.annotation.SuppressLint;
import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.net.http.X509TrustManagerExtensions;
import android.os.Build;
import android.security.KeyChain;
import android.util.Log;
import android.util.Pair;

import org.chromium.base.JNINamespace;

import java.io.ByteArrayInputStream;
import java.io.File;
import java.io.IOException;
import java.security.KeyStore;
import java.security.KeyStoreException;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.security.PublicKey;
import java.security.cert.Certificate;
import java.security.cert.CertificateException;
import java.security.cert.CertificateExpiredException;
import java.security.cert.CertificateFactory;
import java.security.cert.CertificateNotYetValidException;
import java.security.cert.X509Certificate;
import java.util.Arrays;
import java.util.Collections;
import java.util.HashSet;
import java.util.List;
import java.util.Set;

import javax.net.ssl.TrustManager;
import javax.net.ssl.TrustManagerFactory;
import javax.net.ssl.X509TrustManager;
import javax.security.auth.x500.X500Principal;

/**
 * Utility functions for verifying X.509 certificates.
 */
@JNINamespace("net")
public class X509Util {

    private static final String TAG = "X509Util";

    private static final class TrustStorageListener extends BroadcastReceiver {
        @Override public void onReceive(Context context, Intent intent) {
            if (intent.getAction().equals(KeyChain.ACTION_STORAGE_CHANGED)) {
                try {
                    reloadDefaultTrustManager();
                }
                catch (CertificateException e) {
                    Log.e(TAG, "Unable to reload the default TrustManager", e);
                }
                catch (KeyStoreException e) {
                    Log.e(TAG, "Unable to reload the default TrustManager", e);
                }
                catch (NoSuchAlgorithmException e) {
                    Log.e(TAG, "Unable to reload the default TrustManager", e);
                }
            }
        }
    }

    /**
     * Interface that wraps one of X509TrustManager or
     * X509TrustManagerExtensions to support platforms before the latter was
     * added.
     */
    private static interface X509TrustManagerImplementation {
        public List<X509Certificate> checkServerTrusted(X509Certificate[] chain,
                                                        String authType,
                                                        String host) throws CertificateException;
    }

    private static final class X509TrustManagerIceCreamSandwich implements
            X509TrustManagerImplementation {
        private final X509TrustManager mTrustManager;

        public X509TrustManagerIceCreamSandwich(X509TrustManager trustManager) {
            mTrustManager = trustManager;
        }

        @Override
        public List<X509Certificate> checkServerTrusted(X509Certificate[] chain,
                                                        String authType,
                                                        String host) throws CertificateException {
            mTrustManager.checkServerTrusted(chain, authType);
            return Collections.<X509Certificate>emptyList();
        }
    }

    private static final class X509TrustManagerJellyBean implements X509TrustManagerImplementation {
        private final X509TrustManagerExtensions mTrustManagerExtensions;

        @SuppressLint("NewApi")
        public X509TrustManagerJellyBean(X509TrustManager trustManager) {
            mTrustManagerExtensions = new X509TrustManagerExtensions(trustManager);
        }

        @Override
        public List<X509Certificate> checkServerTrusted(X509Certificate[] chain,
                                                        String authType,
                                                        String host) throws CertificateException {
            return mTrustManagerExtensions.checkServerTrusted(chain, authType, host);
        }
    }

    private static CertificateFactory sCertificateFactory;

    private static final String OID_TLS_SERVER_AUTH = "1.3.6.1.5.5.7.3.1";
    private static final String OID_ANY_EKU = "2.5.29.37.0";
    // Server-Gated Cryptography (necessary to support a few legacy issuers):
    //    Netscape:
    private static final String OID_SERVER_GATED_NETSCAPE = "2.16.840.1.113730.4.1";
    //    Microsoft:
    private static final String OID_SERVER_GATED_MICROSOFT = "1.3.6.1.4.1.311.10.3.3";

    /**
     * Trust manager backed up by the read-only system certificate store.
     */
    private static X509TrustManagerImplementation sDefaultTrustManager;

    /**
     * BroadcastReceiver that listens to change in the system keystore to invalidate certificate
     * caches.
     */
    private static TrustStorageListener sTrustStorageListener;

    /**
     * Trust manager backed up by a custom certificate store. We need such manager to plant test
     * root CA to the trust store in testing.
     */
    private static X509TrustManagerImplementation sTestTrustManager;
    private static KeyStore sTestKeyStore;

    /**
     * The system key store. This is used to determine whether a trust anchor is a system trust
     * anchor or user-installed.
     */
    private static KeyStore sSystemKeyStore;

    /**
     * The directory where system certificates are stored. This is used to determine whether a
     * trust anchor is a system trust anchor or user-installed. The KeyStore API alone is not
     * sufficient to efficiently query whether a given X500Principal, PublicKey pair is a trust
     * anchor.
     */
    private static File sSystemCertificateDirectory;

    /**
     * An in-memory cache of which trust anchors are system trust roots. This avoids reading and
     * decoding the root from disk on every verification. Mirrors a similar in-memory cache in
     * Conscrypt's X509TrustManager implementation.
     */
    private static Set<Pair<X500Principal, PublicKey>> sSystemTrustAnchorCache;

    /**
     * True if the system key store has been loaded. If the "AndroidCAStore" KeyStore instance
     * was not found, sSystemKeyStore may be null while sLoadedSystemKeyStore is true.
     */
    private static boolean sLoadedSystemKeyStore;

    /**
     * Lock object used to synchronize all calls that modify or depend on the trust managers.
     */
    private static final Object sLock = new Object();

    /**
     * Allow disabling registering the observer and recording histograms for the certificate
     * changes. Net unit tests do not load native libraries which prevent this to succeed. Moreover,
     * the system does not allow to interact with the certificate store without user interaction.
     */
    private static boolean sDisableNativeCodeForTest = false;

    /**
     * Ensures that the trust managers and certificate factory are initialized.
     */
    private static void ensureInitialized() throws CertificateException,
            KeyStoreException, NoSuchAlgorithmException {
        synchronized (sLock) {
            if (sCertificateFactory == null) {
                sCertificateFactory = CertificateFactory.getInstance("X.509");
            }
            if (sDefaultTrustManager == null) {
                sDefaultTrustManager = X509Util.createTrustManager(null);
            }
            if (!sLoadedSystemKeyStore) {
                try {
                    sSystemKeyStore = KeyStore.getInstance("AndroidCAStore");
                    try {
                        sSystemKeyStore.load(null);
                    } catch (IOException e) {
                        // No IO operation is attempted.
                    }
                    sSystemCertificateDirectory =
                            new File(System.getenv("ANDROID_ROOT") + "/etc/security/cacerts");
                } catch (KeyStoreException e) {
                    // Could not load AndroidCAStore. Continue anyway; isKnownRoot will always
                    // return false.
                }
                if (!sDisableNativeCodeForTest)
                    nativeRecordCertVerifyCapabilitiesHistogram(sSystemKeyStore != null);
                sLoadedSystemKeyStore = true;
            }
            if (sSystemTrustAnchorCache == null) {
                sSystemTrustAnchorCache = new HashSet<Pair<X500Principal, PublicKey>>();
            }
            if (sTestKeyStore == null) {
                sTestKeyStore = KeyStore.getInstance(KeyStore.getDefaultType());
                try {
                    sTestKeyStore.load(null);
                } catch (IOException e) {
                    // No IO operation is attempted.
                }
            }
            if (sTestTrustManager == null) {
                sTestTrustManager = X509Util.createTrustManager(sTestKeyStore);
            }
            if (!sDisableNativeCodeForTest && sTrustStorageListener == null) {
                sTrustStorageListener = new TrustStorageListener();
                nativeGetApplicationContext().registerReceiver(sTrustStorageListener,
                        new IntentFilter(KeyChain.ACTION_STORAGE_CHANGED));
            }
        }
    }

    /**
     * Creates a X509TrustManagerImplementation backed up by the given key
     * store. When null is passed as a key store, system default trust store is
     * used.
     * @throws KeyStoreException, NoSuchAlgorithmException on error initializing the TrustManager.
     */
    private static X509TrustManagerImplementation createTrustManager(KeyStore keyStore) throws
            KeyStoreException, NoSuchAlgorithmException {
        String algorithm = TrustManagerFactory.getDefaultAlgorithm();
        TrustManagerFactory tmf = TrustManagerFactory.getInstance(algorithm);
        tmf.init(keyStore);

        for (TrustManager tm : tmf.getTrustManagers()) {
            if (tm instanceof X509TrustManager) {
                try {
                    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN_MR1) {
                        return new X509TrustManagerJellyBean((X509TrustManager) tm);
                    } else {
                        return new X509TrustManagerIceCreamSandwich((X509TrustManager) tm);
                    }
                } catch (IllegalArgumentException e) {
                    Log.e(TAG, "Error creating trust manager: " + e);
                }
            }
        }
        return null;
    }

    /**
     * After each modification of test key store, trust manager has to be generated again.
     */
    private static void reloadTestTrustManager() throws KeyStoreException,
            NoSuchAlgorithmException {
        sTestTrustManager = X509Util.createTrustManager(sTestKeyStore);
    }

    /**
     * After each modification by the system of the key store, trust manager has to be regenerated.
     */
    private static void reloadDefaultTrustManager() throws KeyStoreException,
            NoSuchAlgorithmException, CertificateException {
        sDefaultTrustManager = null;
        sSystemTrustAnchorCache = null;
        nativeNotifyKeyChainChanged();
        ensureInitialized();
    }

    /**
     * Convert a DER encoded certificate to an X509Certificate.
     */
    public static X509Certificate createCertificateFromBytes(byte[] derBytes) throws
            CertificateException, KeyStoreException, NoSuchAlgorithmException {
        ensureInitialized();
        return (X509Certificate) sCertificateFactory.generateCertificate(
                new ByteArrayInputStream(derBytes));
    }

    public static void addTestRootCertificate(byte[] rootCertBytes) throws CertificateException,
            KeyStoreException, NoSuchAlgorithmException {
        ensureInitialized();
        X509Certificate rootCert = createCertificateFromBytes(rootCertBytes);
        synchronized (sLock) {
            sTestKeyStore.setCertificateEntry(
                    "root_cert_" + Integer.toString(sTestKeyStore.size()), rootCert);
            reloadTestTrustManager();
        }
    }

    public static void clearTestRootCertificates() throws NoSuchAlgorithmException,
            CertificateException, KeyStoreException {
        ensureInitialized();
        synchronized (sLock) {
            try {
                sTestKeyStore.load(null);
                reloadTestTrustManager();
            } catch (IOException e) {
                // No IO operation is attempted.
            }
        }
    }

    private static final char[] HEX_DIGITS = {
        '0', '1', '2', '3', '4', '5', '6', '7', '8', '9',
        'a', 'b', 'c', 'd', 'e', 'f',
    };

    private static String hashPrincipal(X500Principal principal) throws NoSuchAlgorithmException {
        // Android hashes a principal as the first four bytes of its MD5 digest, encoded in
        // lowercase hex and reversed. Verified in 4.2, 4.3, and 4.4.
        byte[] digest = MessageDigest.getInstance("MD5").digest(principal.getEncoded());
        char[] hexChars = new char[8];
        for (int i = 0; i < 4; i++) {
            hexChars[2 * i] = HEX_DIGITS[(digest[3 - i] >> 4) & 0xf];
            hexChars[2 * i + 1] = HEX_DIGITS[digest[3 - i] & 0xf];
        }
        return new String(hexChars);
    }

    private static boolean isKnownRoot(X509Certificate root)
            throws NoSuchAlgorithmException, KeyStoreException {
        // Could not find the system key store. Conservatively report false.
        if (sSystemKeyStore == null)
            return false;

        // Check the in-memory cache first; avoid decoding the anchor from disk
        // if it has been seen before.
        Pair<X500Principal, PublicKey> key =
            new Pair<X500Principal, PublicKey>(root.getSubjectX500Principal(), root.getPublicKey());
        if (sSystemTrustAnchorCache.contains(key))
            return true;

        // Note: It is not sufficient to call sSystemKeyStore.getCertificiateAlias. If the server
        // supplies a copy of a trust anchor, X509TrustManagerExtensions returns the server's
        // version rather than the system one. getCertificiateAlias will then fail to find an anchor
        // name. This is fixed upstream in https://android-review.googlesource.com/#/c/91605/
        //
        // TODO(davidben): When the change trickles into an Android release, query sSystemKeyStore
        // directly.

        // System trust anchors are stored under a hash of the principal. In case of collisions,
        // a number is appended.
        String hash = hashPrincipal(root.getSubjectX500Principal());
        for (int i = 0; true; i++) {
            String alias = hash + '.' + i;
            if (!new File(sSystemCertificateDirectory, alias).exists())
                break;

            Certificate anchor = sSystemKeyStore.getCertificate("system:" + alias);
            // It is possible for this to return null if the user deleted a trust anchor. In
            // that case, the certificate remains in the system directory but is also added to
            // another file. Continue iterating as there may be further collisions after the
            // deleted anchor.
            if (anchor == null)
                continue;

            if (!(anchor instanceof X509Certificate)) {
                // This should never happen.
                String className = anchor.getClass().getName();
                Log.e(TAG, "Anchor " + alias + " not an X509Certificate: " + className);
                continue;
            }

            // If the subject and public key match, this is a system root.
            X509Certificate anchorX509 = (X509Certificate)anchor;
            if (root.getSubjectX500Principal().equals(anchorX509.getSubjectX500Principal()) &&
                root.getPublicKey().equals(anchorX509.getPublicKey())) {
                sSystemTrustAnchorCache.add(key);
                return true;
            }
        }

        return false;
    }

    /**
     * If an EKU extension is present in the end-entity certificate, it MUST contain either the
     * anyEKU or serverAuth or netscapeSGC or Microsoft SGC EKUs.
     *
     * @return true if there is no EKU extension or if any of the EKU extensions is one of the valid
     * OIDs for web server certificates.
     *
     * TODO(palmer): This can be removed after the equivalent change is made to the Android default
     * TrustManager and that change is shipped to a large majority of Android users.
     */
    static boolean verifyKeyUsage(X509Certificate certificate) throws CertificateException {
        List<String> ekuOids;
        try {
            ekuOids = certificate.getExtendedKeyUsage();
        } catch (NullPointerException e) {
            // getExtendedKeyUsage() can crash due to an Android platform bug. This probably
            // happens when the EKU extension data is malformed so return false here.
            // See http://crbug.com/233610
            return false;
        }
        if (ekuOids == null)
            return true;

        for (String ekuOid : ekuOids) {
            if (ekuOid.equals(OID_TLS_SERVER_AUTH) ||
                ekuOid.equals(OID_ANY_EKU) ||
                ekuOid.equals(OID_SERVER_GATED_NETSCAPE) ||
                ekuOid.equals(OID_SERVER_GATED_MICROSOFT)) {
                return true;
            }
        }

        return false;
    }

    public static AndroidCertVerifyResult verifyServerCertificates(byte[][] certChain,
                                                                   String authType,
                                                                   String host)
            throws KeyStoreException, NoSuchAlgorithmException {
        if (certChain == null || certChain.length == 0 || certChain[0] == null) {
            throw new IllegalArgumentException("Expected non-null and non-empty certificate " +
                    "chain passed as |certChain|. |certChain|=" + Arrays.deepToString(certChain));
        }


        try {
            ensureInitialized();
        } catch (CertificateException e) {
            return new AndroidCertVerifyResult(CertVerifyStatusAndroid.VERIFY_FAILED);
        }

        X509Certificate[] serverCertificates = new X509Certificate[certChain.length];
        try {
            for (int i = 0; i < certChain.length; ++i) {
                serverCertificates[i] = createCertificateFromBytes(certChain[i]);
            }
        } catch (CertificateException e) {
            return new AndroidCertVerifyResult(CertVerifyStatusAndroid.VERIFY_UNABLE_TO_PARSE);
        }

        // Expired and not yet valid certificates would be rejected by the trust managers, but the
        // trust managers report all certificate errors using the general CertificateException. In
        // order to get more granular error information, cert validity time range is being checked
        // separately.
        try {
            serverCertificates[0].checkValidity();
            if (!verifyKeyUsage(serverCertificates[0])) {
                return new AndroidCertVerifyResult(
                        CertVerifyStatusAndroid.VERIFY_INCORRECT_KEY_USAGE);
            }
        } catch (CertificateExpiredException e) {
            return new AndroidCertVerifyResult(CertVerifyStatusAndroid.VERIFY_EXPIRED);
        } catch (CertificateNotYetValidException e) {
            return new AndroidCertVerifyResult(CertVerifyStatusAndroid.VERIFY_NOT_YET_VALID);
        } catch (CertificateException e) {
            return new AndroidCertVerifyResult(CertVerifyStatusAndroid.VERIFY_FAILED);
        }

        synchronized (sLock) {
            List<X509Certificate> verifiedChain;
            try {
                verifiedChain = sDefaultTrustManager.checkServerTrusted(serverCertificates,
                                                                        authType, host);
            } catch (CertificateException eDefaultManager) {
                try {
                    verifiedChain = sTestTrustManager.checkServerTrusted(serverCertificates,
                                                                         authType, host);
                } catch (CertificateException eTestManager) {
                    // Neither of the trust managers confirms the validity of the certificate chain,
                    // log the error message returned by the system trust manager.
                    Log.i(TAG, "Failed to validate the certificate chain, error: " +
                              eDefaultManager.getMessage());
                    return new AndroidCertVerifyResult(
                            CertVerifyStatusAndroid.VERIFY_NO_TRUSTED_ROOT);
                }
            }

            boolean isIssuedByKnownRoot = false;
            if (verifiedChain.size() > 0) {
                X509Certificate root = verifiedChain.get(verifiedChain.size() - 1);
                isIssuedByKnownRoot = isKnownRoot(root);
            }

            return new AndroidCertVerifyResult(CertVerifyStatusAndroid.VERIFY_OK,
                                               isIssuedByKnownRoot, verifiedChain);
        }
    }

    public static void setDisableNativeCodeForTest(boolean disabled) {
        sDisableNativeCodeForTest = disabled;
    }
    /**
     * Notify the native net::CertDatabase instance that the system database has been updated.
     */
    private static native void nativeNotifyKeyChainChanged();

    /**
     * Record histograms on the platform's certificate verification capabilities.
     */
    private static native void nativeRecordCertVerifyCapabilitiesHistogram(
        boolean foundSystemTrustRoots);

    /**
     * Returns the application context.
     */
    private static native Context nativeGetApplicationContext();

}