java/src/main/java/com/google/crypto/tink/aead/AesCtrKeyManager.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.aead;

import com.google.crypto.tink.KeyTypeManager;
import com.google.crypto.tink.Registry;
import com.google.crypto.tink.proto.AesCtrKey;
import com.google.crypto.tink.proto.AesCtrKeyFormat;
import com.google.crypto.tink.proto.AesCtrParams;
import com.google.crypto.tink.proto.KeyData.KeyMaterialType;
import com.google.crypto.tink.subtle.AesCtrJceCipher;
import com.google.crypto.tink.subtle.IndCpaCipher;
import com.google.crypto.tink.subtle.Random;
import com.google.crypto.tink.subtle.Validators;
import com.google.protobuf.ByteString;
import com.google.protobuf.InvalidProtocolBufferException;
import java.security.GeneralSecurityException;

/**
 * This key manager generates new {@code AesCtrKey} keys and produces new instances of {@code
 * AesCtrJceCipher}.
 */
public class AesCtrKeyManager extends KeyTypeManager<AesCtrKey> {
  AesCtrKeyManager() {
    super(
        AesCtrKey.class,
        new PrimitiveFactory<IndCpaCipher, AesCtrKey>(IndCpaCipher.class) {
          @Override
          public IndCpaCipher getPrimitive(AesCtrKey key) throws GeneralSecurityException {
            return new AesCtrJceCipher(
                key.getKeyValue().toByteArray(), key.getParams().getIvSize());
          }
        });
  }

  // In counter mode each message is encrypted with an initialization vector (IV) that must be
  // unique. If one single IV is ever used to encrypt two or more messages, the confidentiality of
  // these messages might be lost. This cipher uses a randomly generated IV for each message. The
  // birthday paradox says that if one encrypts 2^k messages, the probability that the random IV
  // will repeat is roughly 2^{2k - t}, where t is the size in bits of the IV. Thus with 96-bit
  // (12-byte) IV, if one encrypts 2^32 messages the probability of IV collision is less than
  // 2^-33 (i.e., less than one in eight billion).
  private static final int MIN_IV_SIZE_IN_BYTES = 12;

  @Override
  public String getKeyType() {
    return "type.googleapis.com/google.crypto.tink.AesCtrKey";
  }

  @Override
  public int getVersion() {
    return 0;
  }

  @Override
  public KeyMaterialType keyMaterialType() {
    return KeyMaterialType.SYMMETRIC;
  }

  @Override
  public void validateKey(AesCtrKey key) throws GeneralSecurityException {
    Validators.validateVersion(key.getVersion(), getVersion());
    Validators.validateAesKeySize(key.getKeyValue().size());
    validateParams(key.getParams());
  }

  @Override
  public AesCtrKey parseKey(ByteString byteString) throws InvalidProtocolBufferException {
    return AesCtrKey.parseFrom(byteString);
  }

  @Override
  public KeyFactory<AesCtrKeyFormat, AesCtrKey> keyFactory() {
    return new KeyFactory<AesCtrKeyFormat, AesCtrKey>(AesCtrKeyFormat.class) {
      @Override
      public void validateKeyFormat(AesCtrKeyFormat format) throws GeneralSecurityException {
        Validators.validateAesKeySize(format.getKeySize());
        validateParams(format.getParams());
      }

      @Override
      public AesCtrKeyFormat parseKeyFormat(ByteString byteString)
          throws InvalidProtocolBufferException {
        return AesCtrKeyFormat.parseFrom(byteString);
      }

      @Override
      public AesCtrKey createKey(AesCtrKeyFormat format) throws GeneralSecurityException {
        return AesCtrKey.newBuilder()
            .setParams(format.getParams())
            .setKeyValue(ByteString.copyFrom(Random.randBytes(format.getKeySize())))
            .setVersion(getVersion())
            .build();
      }
    };
  }

  private void validateParams(AesCtrParams params) throws GeneralSecurityException {
    if (params.getIvSize() < MIN_IV_SIZE_IN_BYTES || params.getIvSize() > 16) {
      throw new GeneralSecurityException("invalid IV size");
    }
  }

  public static void register(boolean newKeyAllowed) throws GeneralSecurityException {
    Registry.registerKeyManager(new AesCtrKeyManager(), newKeyAllowed);
  }
}