java/src/main/java/com/google/crypto/tink/integration/gcpkms/GcpKmsClient.java

// Copyright 2017 Google Inc.
//
// 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 com.google.crypto.tink.integration.gcpkms;

import com.google.api.client.googleapis.auth.oauth2.GoogleCredential;
import com.google.api.client.http.javanet.NetHttpTransport;
import com.google.api.client.json.jackson2.JacksonFactory;
import com.google.api.services.cloudkms.v1.CloudKMS;
import com.google.api.services.cloudkms.v1.CloudKMSScopes;
import com.google.auto.service.AutoService;
import com.google.crypto.tink.Aead;
import com.google.crypto.tink.KmsClient;
import com.google.crypto.tink.Version;
import com.google.crypto.tink.subtle.Validators;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.security.GeneralSecurityException;

/**
 * An implementation of {@code KmsClient} for <a href="https://cloud.google.com/kms/">Google Cloud
 * KMS</a>.
 *
 * @since 1.0.0
 */
@AutoService(KmsClient.class)
public final class GcpKmsClient implements KmsClient {
  /** The prefix of all keys stored in Google Cloud KMS. */
  public static final String PREFIX = "gcp-kms://";

  private static final String APPLICATION_NAME = "Tink/" + Version.TINK_VERSION;
  private CloudKMS client;
  private String keyUri;

  /** Constructs a generic GcpKmsClient that is not bound to any specific key. */
  public GcpKmsClient() {}

  /** Constructs a specific GcpKmsClient that is bound to a single key identified by {@code uri}. */
  public GcpKmsClient(String uri) {
    if (!uri.toLowerCase().startsWith(PREFIX)) {
      throw new IllegalArgumentException("key URI must starts with " + PREFIX);
    }
    this.keyUri = uri;
  }

  /**
   * @return @return true either if this client is a generic one and uri starts with {@link
   *     GcpKmsClient#PREFIX}, or the client is a specific one that is bound to the key identified
   *     by {@code uri}
   */
  @Override
  public boolean doesSupport(String uri) {
    if (this.keyUri != null && this.keyUri.equals(uri)) {
      return true;
    }
    return this.keyUri == null && uri.toLowerCase().startsWith(PREFIX);
  }

  /**
   * Loads credentials from a service account JSON file {@code credentialPath}.
   *
   * <p>If {@code credentialPath} is null, loads <a
   * href="https://developers.google.com/accounts/docs/application-default-credentials" default
   * Google Cloud credentials</a>.
   */
  @Override
  public KmsClient withCredentials(String credentialPath) throws GeneralSecurityException {
    if (credentialPath == null) {
      return withDefaultCredentials();
    }
    try {
      GoogleCredential credentials =
          GoogleCredential.fromStream(
              new FileInputStream(new File(credentialPath)));
      return withCredentials(credentials);
    } catch (IOException e) {
      throw new GeneralSecurityException("cannot load credentials", e);
    }
  }

  /**
   * Loads <a href="https://developers.google.com/accounts/docs/application-default-credentials"
   * default Google Cloud credentials</a>.
   */
  @Override
  public KmsClient withDefaultCredentials() throws GeneralSecurityException {
    try {
      GoogleCredential credentials =
          GoogleCredential.getApplicationDefault(new NetHttpTransport(), new JacksonFactory());
      return withCredentials(credentials);
    } catch (IOException e) {
      throw new GeneralSecurityException("cannot load default credentials", e);
    }
  }

  /** Loads the provided credential. */
  private KmsClient withCredentials(GoogleCredential credential) {
    if (credential.createScopedRequired()) {
      credential = credential.createScoped(CloudKMSScopes.all());
    }
    this.client =
        new CloudKMS.Builder(new NetHttpTransport(), new JacksonFactory(), credential)
            .setApplicationName(APPLICATION_NAME)
            .build();
    return this;
  }

  @Override
  public Aead getAead(String uri) throws GeneralSecurityException {
    if (this.keyUri != null && !this.keyUri.equals(uri)) {
      throw new GeneralSecurityException(
          String.format("this client is bound to %s, cannot load keys bound to %s",
              this.keyUri, uri));
    }
    return new GcpKmsAead(client, Validators.validateKmsKeyUriAndRemovePrefix(PREFIX, uri));
  }
}