Registering multiple keystores in JVM

Question

I have two applications running in the same java virtual machine, and both use different keystores and truststores.

A viable option would be use a single keystore an

Answer 1

Raz's answer was a great start, but wasn't quite flexible enough to meet my needs. The MultiStoreKeyManager explicitly checks the custom KeyManager and then falls back to the jvm KeyManager if an operation fails. I actually want to check jvm certs first; the best solution should be able to handle either case. Additionally, the answer fails to provide a working TrustManager.

I've written a couple more flexible classes, CompositeX509KeyManager and CompositeX509TrustManager, which add support for any number of keystores in an arbitrary order.

CompositeX509KeyManager

package com.mycompany.ssl;

import java.net.Socket;
import java.security.Principal;
import java.security.PrivateKey;
import java.security.cert.X509Certificate;
import java.util.List;

import javax.annotation.Nullable;
import javax.net.ssl.X509KeyManager;

import com.google.common.collect.ImmutableList;
import com.google.common.collect.Iterables;

/**
 * Represents an ordered list of {@link X509KeyManager}s with most-preferred managers first.
 *
 * This is necessary because of the fine-print on {@link SSLContext#init}:
 *     Only the first instance of a particular key and/or trust manager implementation type in the
 *     array is used. (For example, only the first javax.net.ssl.X509KeyManager in the array will be used.)
 *
 * @author codyaray
 * @since 4/22/2013
 * @see http://stackoverflow.com/questions/1793979/registering-multiple-keystores-in-jvm
 */
public class CompositeX509KeyManager implements X509KeyManager {

  private final List keyManagers;

  /**
   * Creates a new {@link CompositeX509KeyManager}.
   *
   * @param keyManagers the X509 key managers, ordered with the most-preferred managers first.
   */
  public CompositeX509KeyManager(List keyManagers) {
    this.keyManagers = ImmutableList.copyOf(keyManagers);
  }

  /**
   * Chooses the first non-null client alias returned from the delegate
   * {@link X509TrustManagers}, or {@code null} if there are no matches.
   */
  @Override
  public @Nullable String chooseClientAlias(String[] keyType, Principal[] issuers, Socket socket) {
    for (X509KeyManager keyManager : keyManagers) {
      String alias = keyManager.chooseClientAlias(keyType, issuers, socket);
      if (alias != null) {
        return alias;
      }
    }
    return null;
  }

  /**
   * Chooses the first non-null server alias returned from the delegate
   * {@link X509TrustManagers}, or {@code null} if there are no matches.
   */
  @Override
  public @Nullable String chooseServerAlias(String keyType, Principal[] issuers, Socket socket) {
    for (X509KeyManager keyManager : keyManagers) {
      String alias = keyManager.chooseServerAlias(keyType, issuers, socket);
      if (alias != null) {
        return alias;
      }
    }
    return null;
  }

  /**
   * Returns the first non-null private key associated with the
   * given alias, or {@code null} if the alias can't be found.
   */
  @Override
  public @Nullable PrivateKey getPrivateKey(String alias) {
    for (X509KeyManager keyManager : keyManagers) {
      PrivateKey privateKey = keyManager.getPrivateKey(alias);
      if (privateKey != null) {
        return privateKey;
      }
    }
    return null;
  }

  /**
   * Returns the first non-null certificate chain associated with the
   * given alias, or {@code null} if the alias can't be found.
   */
  @Override
  public @Nullable X509Certificate[] getCertificateChain(String alias) {
    for (X509KeyManager keyManager : keyManagers) {
      X509Certificate[] chain = keyManager.getCertificateChain(alias);
      if (chain != null && chain.length > 0) {
        return chain;
      }
    }
    return null;
  }

  /**
   * Get all matching aliases for authenticating the client side of a
   * secure socket, or {@code null} if there are no matches.
   */
  @Override
  public @Nullable String[] getClientAliases(String keyType, Principal[] issuers) {
    ImmutableList.Builder aliases = ImmutableList.builder();
    for (X509KeyManager keyManager : keyManagers) {
      aliases.add(keyManager.getClientAliases(keyType, issuers));
    }
    return emptyToNull(Iterables.toArray(aliases.build(), String.class));
  }

  /**
   * Get all matching aliases for authenticating the server side of a
   * secure socket, or {@code null} if there are no matches.
   */
  @Override
  public @Nullable String[] getServerAliases(String keyType, Principal[] issuers) {
    ImmutableList.Builder aliases = ImmutableList.builder();
    for (X509KeyManager keyManager : keyManagers) {
      aliases.add(keyManager.getServerAliases(keyType, issuers));
    }
    return emptyToNull(Iterables.toArray(aliases.build(), String.class));
  }

  @Nullable
  private static  T[] emptyToNull(T[] arr) {
    return (arr.length == 0) ? null : arr;
  }

}

CompositeX509TrustManager

package com.mycompany.ssl;

import java.security.cert.CertificateException;
import java.security.cert.X509Certificate;
import java.util.List;

import javax.net.ssl.X509TrustManager;

import com.google.common.collect.ImmutableList;
import com.google.common.collect.Iterables;

/**
 * Represents an ordered list of {@link X509TrustManager}s with additive trust. If any one of the
 * composed managers trusts a certificate chain, then it is trusted by the composite manager.
 *
 * This is necessary because of the fine-print on {@link SSLContext#init}:
 *     Only the first instance of a particular key and/or trust manager implementation type in the
 *     array is used. (For example, only the first javax.net.ssl.X509KeyManager in the array will be used.)
 *
 * @author codyaray
 * @since 4/22/2013
 * @see http://stackoverflow.com/questions/1793979/registering-multiple-keystores-in-jvm
 */
public class CompositeX509TrustManager implements X509TrustManager {

  private final List trustManagers;

  public CompositeX509TrustManager(List trustManagers) {
    this.trustManagers = ImmutableList.copyOf(trustManagers);
  }

  @Override
  public void checkClientTrusted(X509Certificate[] chain, String authType) throws CertificateException {
    for (X509TrustManager trustManager : trustManagers) {
      try {
        trustManager.checkClientTrusted(chain, authType);
        return; // someone trusts them. success!
      } catch (CertificateException e) {
        // maybe someone else will trust them
      }
    }
    throw new CertificateException("None of the TrustManagers trust this certificate chain");
  }

  @Override
  public void checkServerTrusted(X509Certificate[] chain, String authType) throws CertificateException {
    for (X509TrustManager trustManager : trustManagers) {
      try {
        trustManager.checkServerTrusted(chain, authType);
        return; // someone trusts them. success!
      } catch (CertificateException e) {
        // maybe someone else will trust them
      }
    }
    throw new CertificateException("None of the TrustManagers trust this certificate chain");
  }

  @Override
  public X509Certificate[] getAcceptedIssuers() {
    ImmutableList.Builder certificates = ImmutableList.builder();
    for (X509TrustManager trustManager : trustManagers) {
      certificates.add(trustManager.getAcceptedIssuers());
    }
    return Iterables.toArray(certificates.build(), X509Certificate.class);
  }

}

Usage

For the standard case of one keystore + jvm keystore, you can wire it up like this. I’m using Guava again, but in a Guicey wrapper this time:

@Provides @Singleton
SSLContext provideSSLContext(KeyStore keystore, char[] password) {
  String defaultAlgorithm = KeyManagerFactory.getDefaultAlgorithm();
  X509KeyManager customKeyManager = getKeyManager("SunX509", keystore, password);
  X509KeyManager jvmKeyManager = getKeyManager(defaultAlgorithm, null, null);
  X509TrustManager customTrustManager = getTrustManager("SunX509", keystore);
  X509TrustManager jvmTrustManager = getTrustManager(defaultAlgorithm, null);

  KeyManager[] keyManagers = { new CompositeX509KeyManager(ImmutableList.of(jvmKeyManager, customKeyManager)) };
  TrustManager[] trustManagers = { new CompositeX509TrustManager(ImmutableList.of(jvmTrustManager, customTrustManager)) };

  SSLContext context = SSLContext.getInstance("SSL");
  context.init(keyManagers, trustManagers, null);
  return context;
}

private X509KeyManager getKeyManager(String algorithm, KeyStore keystore, char[] password) {
  KeyManagerFactory factory = KeyManagerFactory.getInstance(algorithm);
  factory.init(keystore, password);
  return Iterables.getFirst(Iterables.filter(
      Arrays.asList(factory.getKeyManagers()), X509KeyManager.class), null);
}

private X509TrustManager getTrustManager(String algorithm, KeyStore keystore) {
  TrustManagerFactory factory = TrustManagerFactory.getInstance(algorithm);
  factory.init(keystore);
  return Iterables.getFirst(Iterables.filter(
      Arrays.asList(factory.getTrustManagers()), X509TrustManager.class), null); 
}

I extracted this from my blog post about this problem which has a bit more detail, motivation, etc. All the code is there though, so its standalone. :)