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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.kv;
import static com.android.internal.util.Preconditions.checkState;
import com.android.internal.annotations.VisibleForTesting;
import com.android.server.backup.encryption.chunk.ChunkHash;
import com.android.server.backup.encryption.chunking.ChunkHasher;
import com.android.server.backup.encryption.protos.nano.KeyValuePairProto;
import com.android.server.backup.encryption.tasks.DecryptedChunkOutput;
import java.io.IOException;
import java.security.InvalidKeyException;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;
/**
* Builds a key value backup set from plaintext chunks. Computes a digest over the sorted SHA-256
* hashes of the chunks.
*/
public class DecryptedChunkKvOutput implements DecryptedChunkOutput {
@VisibleForTesting static final String DIGEST_ALGORITHM = "SHA-256";
private final ChunkHasher mChunkHasher;
private final List<KeyValuePairProto.KeyValuePair> mUnsortedPairs = new ArrayList<>();
private final List<ChunkHash> mUnsortedHashes = new ArrayList<>();
private boolean mClosed;
/** Constructs a new instance which computers the digest using the given hasher. */
public DecryptedChunkKvOutput(ChunkHasher chunkHasher) {
mChunkHasher = chunkHasher;
}
@Override
public DecryptedChunkOutput open() {
// As we don't have any resources there is nothing to open.
return this;
}
@Override
public void processChunk(byte[] plaintextBuffer, int length)
throws IOException, InvalidKeyException {
checkState(!mClosed, "Cannot process chunk after close()");
KeyValuePairProto.KeyValuePair kvPair = new KeyValuePairProto.KeyValuePair();
KeyValuePairProto.KeyValuePair.mergeFrom(kvPair, plaintextBuffer, 0, length);
mUnsortedPairs.add(kvPair);
// TODO(b/71492289): Update ChunkHasher to accept offset and length so we don't have to copy
// the buffer into a smaller array.
mUnsortedHashes.add(mChunkHasher.computeHash(Arrays.copyOf(plaintextBuffer, length)));
}
@Override
public void close() {
// As we don't have any resources there is nothing to close.
mClosed = true;
}
@Override
public byte[] getDigest() throws NoSuchAlgorithmException {
checkState(mClosed, "Must close() before getDigest()");
MessageDigest digest = getMessageDigest();
Collections.sort(mUnsortedHashes);
for (ChunkHash hash : mUnsortedHashes) {
digest.update(hash.getHash());
}
return digest.digest();
}
private static MessageDigest getMessageDigest() throws NoSuchAlgorithmException {
return MessageDigest.getInstance(DIGEST_ALGORITHM);
}
/**
* Returns the key value pairs from the backup, sorted lexicographically by key.
*
* <p>You must call {@link #close} first.
*/
public List<KeyValuePairProto.KeyValuePair> getPairs() {
checkState(mClosed, "Must close() before getPairs()");
Collections.sort(
mUnsortedPairs,
new Comparator<KeyValuePairProto.KeyValuePair>() {
@Override
public int compare(
KeyValuePairProto.KeyValuePair o1, KeyValuePairProto.KeyValuePair o2) {
return o1.key.compareTo(o2.key);
}
});
return mUnsortedPairs;
}
}
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