// 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.signature;

import com.google.crypto.tink.CryptoFormat;
import com.google.crypto.tink.PrimitiveSet;
import com.google.crypto.tink.PrimitiveWrapper;
import com.google.crypto.tink.PublicKeyVerify;
import com.google.crypto.tink.Registry;
import com.google.crypto.tink.proto.OutputPrefixType;
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 returned primitive works with a keyset (rather than a single key). To verify a signature, the primitive uses the prefix of the signature to efficiently select the right key in the set. If there is no key associated with the prefix or if the keys associated with the prefix do not work, the primitive tries all keys with OutputPrefixType.RAW. 
Since:
1.0.0/**
 * The implementation of {@code PrimitiveWrapper<DeterministicAead>}.
 *
 * <p>The returned primitive works with a keyset (rather than a single key). To verify a signature,
 * the primitive uses the prefix of the signature to efficiently select the right key in the set. If
 * there is no key associated with the prefix or if the keys associated with the prefix do not work,
 * the primitive tries all keys with {@link com.google.crypto.tink.proto.OutputPrefixType#RAW}.
 *
 * @since 1.0.0
 */
class PublicKeyVerifyWrapper implements PrimitiveWrapper<PublicKeyVerify> {
  private static final Logger logger = Logger.getLogger(PublicKeyVerifyWrapper.class.getName());

  private static class WrappedPublicKeyVerify implements PublicKeyVerify {
    private final PrimitiveSet<PublicKeyVerify> primitives;

    public WrappedPublicKeyVerify(PrimitiveSet<PublicKeyVerify> primitives) {
      this.primitives = primitives;
    }

    @Override
    public void verify(final byte[] signature, final byte[] data) throws GeneralSecurityException {
      if (signature.length <= CryptoFormat.NON_RAW_PREFIX_SIZE) {
        // This also rejects raw signatures with size of 4 bytes or fewer. We're not aware of any
        // schemes that output signatures that small.
        throw new GeneralSecurityException("signature too short");
      }
      byte[] prefix = Arrays.copyOfRange(signature, 0, CryptoFormat.NON_RAW_PREFIX_SIZE);
      byte[] sigNoPrefix =
          Arrays.copyOfRange(signature, CryptoFormat.NON_RAW_PREFIX_SIZE, signature.length);
      List<PrimitiveSet.Entry<PublicKeyVerify>> entries = primitives.getPrimitive(prefix);
      for (PrimitiveSet.Entry<PublicKeyVerify> entry : entries) {
        try {
          if (entry.getOutputPrefixType().equals(OutputPrefixType.LEGACY)) {
            final byte[] formatVersion = new byte[] {CryptoFormat.LEGACY_START_BYTE};
            final byte[] dataWithFormatVersion = Bytes.concat(data, formatVersion);
            entry.getPrimitive().verify(sigNoPrefix, dataWithFormatVersion);
          } else {
            entry.getPrimitive().verify(sigNoPrefix, data);
          }
          // If there is no exception, the signature is valid and we can return.
          return;
        } catch (GeneralSecurityException e) {
          logger.info("signature prefix matches a key, but cannot verify: " + e.toString());
          // Ignored as we want to continue verification with the remaining keys.
        }
      }

      // None "non-raw" key matched, so let's try the raw keys (if any exist).
      entries = primitives.getRawPrimitives();
      for (PrimitiveSet.Entry<PublicKeyVerify> entry : entries) {
        try {
          entry.getPrimitive().verify(signature, data);
          // If there is no exception, the signature is valid and we can return.
          return;
        } catch (GeneralSecurityException e) {
          // Ignored as we want to continue verification with raw keys.
        }
      }
      // nothing works.
      throw new GeneralSecurityException("invalid signature");
    }
  }

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

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

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