// 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.hybrid;

import com.google.crypto.tink.CryptoFormat;
import com.google.crypto.tink.HybridDecrypt;
import com.google.crypto.tink.PrimitiveSet;
import com.google.crypto.tink.PrimitiveWrapper;
import com.google.crypto.tink.Registry;
import java.security.GeneralSecurityException;
import java.util.Arrays;
import java.util.List;
import java.util.logging.Logger;

The implementation of PrimitiveWrapper<HybridDecrypt>. 
The returned primitive works with a keyset (rather than a single key). To decrypt, the primitive uses the prefix of the ciphertext to efficiently select the right key in the set. If the keys associated with the prefix do not work, the primitive tries all keys with RAW.RAW. /**
 * The implementation of {@code PrimitiveWrapper<HybridDecrypt>}.
 *
 * <p>The returned primitive works with a keyset (rather than a single key). To decrypt, the
 * primitive uses the prefix of the ciphertext to efficiently select the right key in the set. If
 * the keys associated with the prefix do not work, the primitive tries all keys with {@link
 * com.google.crypto.tink.proto.OutputPrefixType#RAW}.
 */
public class HybridDecryptWrapper implements PrimitiveWrapper<HybridDecrypt> {
  private static final Logger logger = Logger.getLogger(HybridDecryptWrapper.class.getName());

  private static class WrappedHybridDecrypt implements HybridDecrypt {
    private final PrimitiveSet<HybridDecrypt> primitives;

    public WrappedHybridDecrypt(final PrimitiveSet<HybridDecrypt> primitives) {
      this.primitives = primitives;
    }

    @Override
    public byte[] decrypt(final byte[] ciphertext, final byte[] contextInfo)
        throws GeneralSecurityException {
      if (ciphertext.length > CryptoFormat.NON_RAW_PREFIX_SIZE) {
        byte[] prefix = Arrays.copyOfRange(ciphertext, 0, CryptoFormat.NON_RAW_PREFIX_SIZE);
        byte[] ciphertextNoPrefix =
            Arrays.copyOfRange(ciphertext, CryptoFormat.NON_RAW_PREFIX_SIZE, ciphertext.length);
        List<PrimitiveSet.Entry<HybridDecrypt>> entries = primitives.getPrimitive(prefix);
        for (PrimitiveSet.Entry<HybridDecrypt> entry : entries) {
          try {
            return entry.getPrimitive().decrypt(ciphertextNoPrefix, contextInfo);
          } catch (GeneralSecurityException e) {
            logger.info("ciphertext prefix matches a key, but cannot decrypt: " + e.toString());
            continue;
          }
        }
      }
      // Let's try all RAW keys.
      List<PrimitiveSet.Entry<HybridDecrypt>> entries = primitives.getRawPrimitives();
      for (PrimitiveSet.Entry<HybridDecrypt> entry : entries) {
        try {
          return entry.getPrimitive().decrypt(ciphertext, contextInfo);
        } catch (GeneralSecurityException e) {
          continue;
        }
      }
      // nothing works.
      throw new GeneralSecurityException("decryption failed");
    }
  }

  HybridDecryptWrapper() {}

  @Override
  public HybridDecrypt wrap(final PrimitiveSet<HybridDecrypt> primitives) {
    return new WrappedHybridDecrypt(primitives);
  }

  @Override
  public Class<HybridDecrypt> getPrimitiveClass() {
    return HybridDecrypt.class;
  }

  
Register the wrapper within the registry.
This is required for calls to getPrimitive with a HybridDecrypt argument. /**
   * Register the wrapper within the registry.
   *
   * <p>This is required for calls to {@link Keyset.getPrimitive} with a {@link HybridDecrypt}
   * argument.
   */
  public static void register() throws GeneralSecurityException {
    Registry.registerPrimitiveWrapper(new HybridDecryptWrapper());
  }
}