java/src/main/java/com/google/crypto/tink/streamingaead/AesCtrHmacStreamingKeyManager.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.streamingaead;

import com.google.crypto.tink.KeyManagerBase;
import com.google.crypto.tink.StreamingAead;
import com.google.crypto.tink.proto.AesCtrHmacStreamingKey;
import com.google.crypto.tink.proto.AesCtrHmacStreamingKeyFormat;
import com.google.crypto.tink.proto.AesCtrHmacStreamingParams;
import com.google.crypto.tink.proto.HashType;
import com.google.crypto.tink.proto.HmacParams;
import com.google.crypto.tink.proto.KeyData.KeyMaterialType;
import com.google.crypto.tink.subtle.AesCtrHmacStreaming;
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 AesCtrHmacStreamingKey} keys and produces new instances of
 * {@code AesCtrHmacStreaming}.
 */
class AesCtrHmacStreamingKeyManager
    extends KeyManagerBase<StreamingAead, AesCtrHmacStreamingKey, AesCtrHmacStreamingKeyFormat> {
  public AesCtrHmacStreamingKeyManager() {
    super(
        StreamingAead.class,
        AesCtrHmacStreamingKey.class,
        AesCtrHmacStreamingKeyFormat.class,
        TYPE_URL);
  }

  private static final int VERSION = 0;

  public static final String TYPE_URL =
      "type.googleapis.com/google.crypto.tink.AesCtrHmacStreamingKey";

  /** Minimum tag size in bytes. This provides minimum 80-bit security strength. */
  private static final int MIN_TAG_SIZE_IN_BYTES = 10;

  /** @param serializedKey serialized {@code AesCtrHmacStreamingKey} proto */
  @Override
  public StreamingAead getPrimitiveFromKey(AesCtrHmacStreamingKey keyProto)
      throws GeneralSecurityException {
    return new AesCtrHmacStreaming(
        keyProto.getKeyValue().toByteArray(),
        StreamingAeadUtil.toHmacAlgo(
            keyProto.getParams().getHkdfHashType()),
        keyProto.getParams().getDerivedKeySize(),
        StreamingAeadUtil.toHmacAlgo(
            keyProto.getParams().getHmacParams().getHash()),
        keyProto.getParams().getHmacParams().getTagSize(),
        keyProto.getParams().getCiphertextSegmentSize(),
        /* firstSegmentOffset= */ 0);
  }

  /**
   * @param serializedKeyFormat serialized {@code AesCtrHmacStreamingKeyFormat} proto
   * @return new {@code AesCtrHmacStreamingKey} proto
   */
  @Override
  public AesCtrHmacStreamingKey newKeyFromFormat(AesCtrHmacStreamingKeyFormat format)
      throws GeneralSecurityException {
    return AesCtrHmacStreamingKey.newBuilder()
        .setKeyValue(ByteString.copyFrom(Random.randBytes(format.getKeySize())))
        .setParams(format.getParams())
        .setVersion(VERSION)
        .build();
  }

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

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

  @Override
  protected AesCtrHmacStreamingKey parseKeyProto(ByteString byteString)
      throws InvalidProtocolBufferException {
    return AesCtrHmacStreamingKey.parseFrom(byteString);
  }

  @Override
  protected AesCtrHmacStreamingKeyFormat parseKeyFormatProto(ByteString byteString)
      throws InvalidProtocolBufferException {
    return AesCtrHmacStreamingKeyFormat.parseFrom(byteString);
  }

  @Override
  protected void validateKey(AesCtrHmacStreamingKey key) throws GeneralSecurityException {
    Validators.validateVersion(key.getVersion(), VERSION);
    if (key.getKeyValue().size() < 16) {
      throw new GeneralSecurityException("key_value must have at least 16 bytes");
    }
    if (key.getKeyValue().size() < key.getParams().getDerivedKeySize()) {
      throw new GeneralSecurityException(
          "key_value must have at least as many bits as derived keys");
    }
    validate(key.getParams());
  }

  @Override
  protected void validateKeyFormat(AesCtrHmacStreamingKeyFormat format)
      throws GeneralSecurityException {
    if (format.getKeySize() < 16) {
      throw new GeneralSecurityException("key_size must be at least 16 bytes");
    }
    validate(format.getParams());
  }

  private void validate(AesCtrHmacStreamingParams params) throws GeneralSecurityException {
    Validators.validateAesKeySize(params.getDerivedKeySize());
    if (params.getHkdfHashType() == HashType.UNKNOWN_HASH) {
      throw new GeneralSecurityException("unknown HKDF hash type");
    }
    if (params.getHmacParams().getHash() == HashType.UNKNOWN_HASH) {
      throw new GeneralSecurityException("unknown HMAC hash type");
    }
    validateHmacParams(params.getHmacParams());

    if (params.getCiphertextSegmentSize()
        < params.getDerivedKeySize() + params.getHmacParams().getTagSize() + 8) {
      throw new GeneralSecurityException(
          "ciphertext_segment_size must be at least (derived_key_size + tag_size + 8)");
    }
  }

  private void validateHmacParams(HmacParams params) throws GeneralSecurityException {
    if (params.getTagSize() < MIN_TAG_SIZE_IN_BYTES) {
      throw new GeneralSecurityException("tag size too small");
    }
    switch (params.getHash()) {
      case SHA1:
        if (params.getTagSize() > 20) {
          throw new GeneralSecurityException("tag size too big");
        }
        break;
      case SHA256:
        if (params.getTagSize() > 32) {
          throw new GeneralSecurityException("tag size too big");
        }
        break;
      case SHA512:
        if (params.getTagSize() > 64) {
          throw new GeneralSecurityException("tag size too big");
        }
        break;
      default:
        throw new GeneralSecurityException("unknown hash type");
    }
  }
}