// 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.daead;

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

The implementation of PrimitiveWrapper<DeterministicAead>. 
The created primitive works with a keyset (rather than a single key). To encrypt a plaintext, it uses the primary key in the keyset, and prepends to the ciphertext a certain prefix associated with the primary 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 OutputPrefixType.RAW. /**
 * The implementation of {@code PrimitiveWrapper<DeterministicAead>}.
 *
 * <p>The created primitive works with a keyset (rather than a single key). To encrypt a plaintext,
 * it uses the primary key in the keyset, and prepends to the ciphertext a certain prefix associated
 * with the primary 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 DeterministicAeadWrapper implements PrimitiveWrapper<DeterministicAead> {
  private static final Logger logger = Logger.getLogger(DeterministicAeadWrapper.class.getName());

  private static class WrappedDeterministicAead implements DeterministicAead {
    private PrimitiveSet<DeterministicAead> primitives;

    public WrappedDeterministicAead(PrimitiveSet<DeterministicAead> primitives) {
      this.primitives = primitives;
    }

    @Override
    public byte[] encryptDeterministically(final byte[] plaintext, final byte[] associatedData)
        throws GeneralSecurityException {
      return Bytes.concat(
          primitives.getPrimary().getIdentifier(),
          primitives
              .getPrimary()
              .getPrimitive()
              .encryptDeterministically(plaintext, associatedData));
    }

    @Override
    public byte[] decryptDeterministically(final byte[] ciphertext, final byte[] associatedData)
        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<DeterministicAead>> entries = primitives.getPrimitive(prefix);
        for (PrimitiveSet.Entry<DeterministicAead> entry : entries) {
          try {
            return entry
                .getPrimitive()
                .decryptDeterministically(ciphertextNoPrefix, associatedData);
          } 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<DeterministicAead>> entries = primitives.getRawPrimitives();
      for (PrimitiveSet.Entry<DeterministicAead> entry : entries) {
        try {
          return entry.getPrimitive().decryptDeterministically(ciphertext, associatedData);
        } catch (GeneralSecurityException e) {
          continue;
        }
      }
      // nothing works.
      throw new GeneralSecurityException("decryption failed");
    }
  }

  DeterministicAeadWrapper() {}

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

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

  public static void register() throws GeneralSecurityException {
    Registry.registerPrimitiveWrapper(new DeterministicAeadWrapper());
  }
}