| /* |
| * Copyright (C) 2018 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.chunk; |
| |
| import com.android.internal.util.Preconditions; |
| import java.util.Arrays; |
| import java.util.Base64; |
| |
| /** |
| * Represents the SHA-256 hash of the plaintext of a chunk, which is frequently used as a key. |
| * |
| * <p>This class is {@link Comparable} and implements {@link #equals(Object)} and {@link |
| * #hashCode()}. |
| */ |
| public class ChunkHash implements Comparable<ChunkHash> { |
| /** The length of the hash in bytes. The hash is a SHA-256, so this is 256 bits. */ |
| public static final int HASH_LENGTH_BYTES = 256 / 8; |
| |
| private static final int UNSIGNED_MASK = 0xFF; |
| |
| private final byte[] mHash; |
| |
| /** Constructs a new instance which wraps the given SHA-256 hash bytes. */ |
| public ChunkHash(byte[] hash) { |
| Preconditions.checkArgument(hash.length == HASH_LENGTH_BYTES, "Hash must have 256 bits"); |
| mHash = hash; |
| } |
| |
| public byte[] getHash() { |
| return mHash; |
| } |
| |
| @Override |
| public boolean equals(Object o) { |
| if (this == o) { |
| return true; |
| } |
| if (!(o instanceof ChunkHash)) { |
| return false; |
| } |
| |
| ChunkHash chunkHash = (ChunkHash) o; |
| return Arrays.equals(mHash, chunkHash.mHash); |
| } |
| |
| @Override |
| public int hashCode() { |
| return Arrays.hashCode(mHash); |
| } |
| |
| @Override |
| public int compareTo(ChunkHash other) { |
| return lexicographicalCompareUnsignedBytes(getHash(), other.getHash()); |
| } |
| |
| @Override |
| public String toString() { |
| return Base64.getEncoder().encodeToString(mHash); |
| } |
| |
| private static int lexicographicalCompareUnsignedBytes(byte[] left, byte[] right) { |
| int minLength = Math.min(left.length, right.length); |
| for (int i = 0; i < minLength; i++) { |
| int result = toInt(left[i]) - toInt(right[i]); |
| if (result != 0) { |
| return result; |
| } |
| } |
| return left.length - right.length; |
| } |
| |
| private static int toInt(byte value) { |
| return value & UNSIGNED_MASK; |
| } |
| } |