1 files changed, 179 insertions, 0 deletions
diff --git a/packages/BackupEncryption/src/com/android/server/backup/encryption/tasks/KvBackupEncrypter.java b/packages/BackupEncryption/src/com/android/server/backup/encryption/tasks/KvBackupEncrypter.java
new file mode 100644
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+++ b/packages/BackupEncryption/src/com/android/server/backup/encryption/tasks/KvBackupEncrypter.java
@@ -0,0 +1,179 @@
+/*
+ * 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.tasks;
+
+import static com.android.internal.util.Preconditions.checkState;
+
+import android.annotation.Nullable;
+import android.app.backup.BackupDataInput;
+
+import com.android.server.backup.encryption.chunk.ChunkHash;
+import com.android.server.backup.encryption.chunking.ChunkEncryptor;
+import com.android.server.backup.encryption.chunking.ChunkHasher;
+import com.android.server.backup.encryption.chunking.EncryptedChunk;
+import com.android.server.backup.encryption.kv.KeyValueListingBuilder;
+import com.android.server.backup.encryption.protos.nano.KeyValueListingProto;
+import com.android.server.backup.encryption.protos.nano.KeyValuePairProto;
+
+import java.io.IOException;
+import java.security.GeneralSecurityException;
+import java.security.InvalidKeyException;
+import java.security.MessageDigest;
+import java.security.NoSuchAlgorithmException;
+import java.security.SecureRandom;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.Optional;
+import java.util.Set;
+
+import javax.crypto.IllegalBlockSizeException;
+import javax.crypto.SecretKey;
+
+/**
+ * Reads key value backup data from an input, converts each pair into a chunk and encrypts the
+ * chunks.
+ *
+ * <p>The caller should pass in the key value listing from the previous backup, if there is one.
+ * This class emits chunks for both existing and new pairs, using the provided listing to
+ * determine the hashes of pairs that already exist. During the backup it computes the new listing,
+ * which the caller should store on disk and pass in at the start of the next backup.
+ *
+ * <p>Also computes the message digest, which is {@code SHA-256(chunk hashes sorted
+ * lexicographically)}.
+ */
+public class KvBackupEncrypter implements BackupEncrypter {
+    private final BackupDataInput mBackupDataInput;
+
+    private KeyValueListingProto.KeyValueListing mOldKeyValueListing;
+    @Nullable private KeyValueListingBuilder mNewKeyValueListing;
+
+    /**
+     * Constructs a new instance which reads data from the given input.
+     *
+     * <p>By default this performs non-incremental backup, call {@link #setOldKeyValueListing} to
+     * perform incremental backup.
+     */
+    public KvBackupEncrypter(BackupDataInput backupDataInput) {
+        mBackupDataInput = backupDataInput;
+        mOldKeyValueListing = KeyValueListingBuilder.emptyListing();
+    }
+
+    /** Sets the old listing to perform incremental backup against. */
+    public void setOldKeyValueListing(KeyValueListingProto.KeyValueListing oldKeyValueListing) {
+        mOldKeyValueListing = oldKeyValueListing;
+    }
+
+    @Override
+    public Result backup(
+            SecretKey secretKey,
+            @Nullable byte[] unusedFingerprintMixerSalt,
+            Set<ChunkHash> unusedExistingChunks)
+            throws IOException, GeneralSecurityException {
+        ChunkHasher chunkHasher = new ChunkHasher(secretKey);
+        ChunkEncryptor chunkEncryptor = new ChunkEncryptor(secretKey, new SecureRandom());
+        mNewKeyValueListing = new KeyValueListingBuilder();
+        List<ChunkHash> allChunks = new ArrayList<>();
+        List<EncryptedChunk> newChunks = new ArrayList<>();
+
+        Map<String, ChunkHash> existingChunksToReuse = buildPairMap(mOldKeyValueListing);
+
+        while (mBackupDataInput.readNextHeader()) {
+            String key = mBackupDataInput.getKey();
+            Optional<byte[]> value = readEntireValue(mBackupDataInput);
+
+            // As this pair exists in the new backup, we don't need to add it from the previous
+            // backup.
+            existingChunksToReuse.remove(key);
+
+            // If the value is not present then this key has been deleted.
+            if (value.isPresent()) {
+                EncryptedChunk newChunk =
+                        createEncryptedChunk(chunkHasher, chunkEncryptor, key, value.get());
+                allChunks.add(newChunk.key());
+                newChunks.add(newChunk);
+                mNewKeyValueListing.addPair(key, newChunk.key());
+            }
+        }
+
+        allChunks.addAll(existingChunksToReuse.values());
+
+        mNewKeyValueListing.addAll(existingChunksToReuse);
+
+        return new Result(allChunks, newChunks, createMessageDigest(allChunks));
+    }
+
+    /**
+     * Returns a listing containing the pairs in the new backup.
+     *
+     * <p>You must call {@link #backup} first.
+     */
+    public KeyValueListingProto.KeyValueListing getNewKeyValueListing() {
+        checkState(mNewKeyValueListing != null, "Must call backup() first");
+        return mNewKeyValueListing.build();
+    }
+
+    private static Map<String, ChunkHash> buildPairMap(
+            KeyValueListingProto.KeyValueListing listing) {
+        Map<String, ChunkHash> map = new HashMap<>();
+        for (KeyValueListingProto.KeyValueEntry entry : listing.entries) {
+            map.put(entry.key, new ChunkHash(entry.hash));
+        }
+        return map;
+    }
+
+    private EncryptedChunk createEncryptedChunk(
+            ChunkHasher chunkHasher, ChunkEncryptor chunkEncryptor, String key, byte[] value)
+            throws InvalidKeyException, IllegalBlockSizeException {
+        KeyValuePairProto.KeyValuePair pair = new KeyValuePairProto.KeyValuePair();
+        pair.key = key;
+        pair.value = Arrays.copyOf(value, value.length);
+
+        byte[] plaintext = KeyValuePairProto.KeyValuePair.toByteArray(pair);
+        return chunkEncryptor.encrypt(chunkHasher.computeHash(plaintext), plaintext);
+    }
+
+    private static byte[] createMessageDigest(List<ChunkHash> allChunks)
+            throws NoSuchAlgorithmException {
+        MessageDigest messageDigest =
+                MessageDigest.getInstance(BackupEncrypter.MESSAGE_DIGEST_ALGORITHM);
+        // TODO:b/141531271 Extract sorted chunks code to utility class
+        List<ChunkHash> sortedChunks = new ArrayList<>(allChunks);
+        Collections.sort(sortedChunks);
+        for (ChunkHash hash : sortedChunks) {
+            messageDigest.update(hash.getHash());
+        }
+        return messageDigest.digest();
+    }
+
+    private static Optional<byte[]> readEntireValue(BackupDataInput input) throws IOException {
+        // A negative data size indicates that this key should be deleted.
+        if (input.getDataSize() < 0) {
+            return Optional.empty();
+        }
+
+        byte[] value = new byte[input.getDataSize()];
+        int bytesRead = 0;
+        while (bytesRead < value.length) {
+            bytesRead += input.readEntityData(value, bytesRead, value.length - bytesRead);
+        }
+        return Optional.of(value);
+    }
+}