79 lines
2.2 KiB
Java
79 lines
2.2 KiB
Java
/*
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* Copyright (C) 2012 The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package android.content.pm;
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import java.io.FilterInputStream;
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import java.io.IOException;
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import java.io.InputStream;
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import javax.crypto.Mac;
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/**
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* An input stream filter that applies a MAC to the data passing through it. At
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* the end of the data that should be authenticated, the tag can be calculated.
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* After that, the stream should not be used.
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*
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* @hide
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*/
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public class MacAuthenticatedInputStream extends FilterInputStream {
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private final Mac mMac;
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public MacAuthenticatedInputStream(InputStream in, Mac mac) {
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super(in);
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mMac = mac;
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}
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public boolean isTagEqual(byte[] tag) {
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final byte[] actualTag = mMac.doFinal();
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if (tag == null || actualTag == null || tag.length != actualTag.length) {
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return false;
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}
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/*
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* Attempt to prevent timing attacks by doing the same amount of work
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* whether the first byte matches or not. Do not change this to a loop
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* that exits early when a byte does not match.
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*/
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int value = 0;
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for (int i = 0; i < tag.length; i++) {
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value |= tag[i] ^ actualTag[i];
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}
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return value == 0;
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}
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@Override
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public int read() throws IOException {
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final int b = super.read();
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if (b >= 0) {
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mMac.update((byte) b);
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}
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return b;
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}
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@Override
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public int read(byte[] buffer, int offset, int count) throws IOException {
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int numRead = super.read(buffer, offset, count);
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if (numRead > 0) {
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mMac.update(buffer, offset, numRead);
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}
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return numRead;
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}
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}
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