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/*
* 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;
}
}
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