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/*
* Copyright (C) 2019 The Android Open Source Project
*
* 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.android.server.backup.encryption.keys;
import android.annotation.Nullable;
import android.content.Context;
import android.util.Slog;
import com.android.server.backup.encryption.protos.nano.WrappedKeyProto;
import java.io.IOException;
import java.security.InvalidAlgorithmParameterException;
import java.security.InvalidKeyException;
import java.security.NoSuchAlgorithmException;
import java.security.SecureRandom;
import java.util.Optional;
import javax.crypto.IllegalBlockSizeException;
import javax.crypto.NoSuchPaddingException;
import javax.crypto.SecretKey;
/**
* Gets the correct tertiary key to use during a backup, rotating it if required.
*
* <p>Calling any method on this class will count a incremental backup against the app, and the key
* will be rotated if required.
*/
public class TertiaryKeyManager {
private static final String TAG = "TertiaryKeyMgr";
private final TertiaryKeyStore mKeyStore;
private final TertiaryKeyGenerator mKeyGenerator;
private final TertiaryKeyRotationScheduler mTertiaryKeyRotationScheduler;
private final RecoverableKeyStoreSecondaryKey mSecondaryKey;
private final String mPackageName;
private boolean mKeyRotated;
@Nullable private SecretKey mTertiaryKey;
public TertiaryKeyManager(
Context context,
SecureRandom secureRandom,
TertiaryKeyRotationScheduler tertiaryKeyRotationScheduler,
RecoverableKeyStoreSecondaryKey secondaryKey,
String packageName) {
mSecondaryKey = secondaryKey;
mPackageName = packageName;
mKeyGenerator = new TertiaryKeyGenerator(secureRandom);
mKeyStore = TertiaryKeyStore.newInstance(context, secondaryKey);
mTertiaryKeyRotationScheduler = tertiaryKeyRotationScheduler;
}
/**
* Returns either the previously used tertiary key, or a new tertiary key if there was no
* previous key or it needed to be rotated.
*/
public SecretKey getKey()
throws InvalidKeyException, IOException, IllegalBlockSizeException,
NoSuchPaddingException, NoSuchAlgorithmException,
InvalidAlgorithmParameterException {
init();
return mTertiaryKey;
}
/** Returns the key given by {@link #getKey()} wrapped by the secondary key. */
public WrappedKeyProto.WrappedKey getWrappedKey()
throws InvalidKeyException, IOException, IllegalBlockSizeException,
NoSuchPaddingException, NoSuchAlgorithmException,
InvalidAlgorithmParameterException {
init();
return KeyWrapUtils.wrap(mSecondaryKey.getSecretKey(), mTertiaryKey);
}
/**
* Returns {@code true} if a new tertiary key was generated at the start of this session,
* otherwise {@code false}.
*/
public boolean wasKeyRotated()
throws InvalidKeyException, IllegalBlockSizeException, IOException,
NoSuchPaddingException, NoSuchAlgorithmException,
InvalidAlgorithmParameterException {
init();
return mKeyRotated;
}
private void init()
throws IllegalBlockSizeException, InvalidKeyException, IOException,
NoSuchAlgorithmException, NoSuchPaddingException,
InvalidAlgorithmParameterException {
if (mTertiaryKey != null) {
return;
}
Optional<SecretKey> key = getExistingKeyIfNotRotated();
if (!key.isPresent()) {
Slog.d(TAG, "Generating new tertiary key for " + mPackageName);
key = Optional.of(mKeyGenerator.generate());
mKeyRotated = true;
mTertiaryKeyRotationScheduler.recordKeyRotation(mPackageName);
mKeyStore.save(mPackageName, key.get());
}
mTertiaryKey = key.get();
mTertiaryKeyRotationScheduler.recordBackup(mPackageName);
}
private Optional<SecretKey> getExistingKeyIfNotRotated()
throws InvalidKeyException, IOException, InvalidAlgorithmParameterException,
NoSuchAlgorithmException, NoSuchPaddingException {
if (mTertiaryKeyRotationScheduler.isKeyRotationDue(mPackageName)) {
Slog.i(TAG, "Tertiary key rotation was required for " + mPackageName);
return Optional.empty();
} else {
Slog.i(TAG, "Tertiary key rotation was not required");
return mKeyStore.load(mPackageName);
}
}
}
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