| /* |
| * 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.chunking; |
| |
| import com.android.server.backup.encryption.chunk.ChunkHash; |
| |
| import java.security.InvalidKeyException; |
| import java.security.NoSuchAlgorithmException; |
| |
| import javax.crypto.Mac; |
| import javax.crypto.SecretKey; |
| |
| /** Computes the SHA-256 HMAC of a chunk of bytes. */ |
| public class ChunkHasher { |
| private static final String MAC_ALGORITHM = "HmacSHA256"; |
| |
| private final SecretKey mSecretKey; |
| |
| /** Constructs a new hasher which computes the HMAC using the given secret key. */ |
| public ChunkHasher(SecretKey secretKey) { |
| this.mSecretKey = secretKey; |
| } |
| |
| /** Returns the SHA-256 over the given bytes. */ |
| public ChunkHash computeHash(byte[] plaintext) throws InvalidKeyException { |
| try { |
| Mac mac = Mac.getInstance(MAC_ALGORITHM); |
| mac.init(mSecretKey); |
| return new ChunkHash(mac.doFinal(plaintext)); |
| } catch (NoSuchAlgorithmException e) { |
| // This can not happen - AES/GCM/NoPadding is available as part of the framework. |
| throw new AssertionError(e); |
| } |
| } |
| } |