/*
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* Copyright (C) 2018 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 com.android.server.locksettings;
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import java.nio.ByteBuffer;
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import java.security.InvalidKeyException;
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import java.security.NoSuchAlgorithmException;
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import javax.crypto.Mac;
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import javax.crypto.spec.SecretKeySpec;
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/**
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* Implementation of NIST SP800-108
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* "Recommendation for Key Derivation Using Pseudorandom Functions"
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* Hardcoded:
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* [PRF=HMAC_SHA256]
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* [CTRLOCATION=BEFORE_FIXED]
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* [RLEN=32_BITS]
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* L = 256
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* L suffix: 32 bits
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*/
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class SP800Derive {
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private final byte[] mKeyBytes;
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SP800Derive(byte[] keyBytes) {
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mKeyBytes = keyBytes;
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}
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private Mac getMac() {
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try {
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final Mac m = Mac.getInstance("HmacSHA256");
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m.init(new SecretKeySpec(mKeyBytes, m.getAlgorithm()));
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return m;
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} catch (InvalidKeyException | NoSuchAlgorithmException e) {
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throw new RuntimeException(e);
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}
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}
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private static void update32(Mac m, int v) {
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m.update(ByteBuffer.allocate(Integer.BYTES).putInt(v).array());
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}
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/**
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* Generate output from a single, fixed input.
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*/
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public byte[] fixedInput(byte[] fixedInput) {
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final Mac m = getMac();
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update32(m, 1); // Hardwired counter value
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m.update(fixedInput);
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return m.doFinal();
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}
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/**
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* Generate output from a label and context. We add a length field at the end of the context to
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* disambiguate it from the length even in the presence of zero bytes.
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*/
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public byte[] withContext(byte[] label, byte[] context) {
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final Mac m = getMac();
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// Hardwired counter value: 1
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update32(m, 1); // Hardwired counter value
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m.update(label);
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m.update((byte) 0);
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m.update(context);
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update32(m, context.length * 8); // Disambiguate context
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update32(m, 256); // Hardwired output length
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return m.doFinal();
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}
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}
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