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/*
* Copyright (C) 2019 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.ike.crypto;
import java.nio.ByteBuffer;
/**
* KeyGenerationUtils is a util class that contains utils for key generation needed by IKEv2 and
* EAP.
*/
public class KeyGenerationUtils {
/**
* Returns the derived pseudorandom number with the specified length by iteratively applying a
* PRF.
*
* <p>prf+(K, S) outputs a pseudorandom stream by using the PRF iteratively. In this way it can
* generate long enough keying material containing all the keys.
*
* @see <a href="https://tools.ietf.org/html/rfc7296#section-2.13">RFC 7296 Internet Key
* Exchange Protocol Version 2 (IKEv2) 2.13. Generating Keying Material </a>
* @param byteSigner the PRF used to sign the given data using the given key.
* @param keyBytes the key to sign data.
* @param dataToSign the data to be signed.
* @param keyMaterialLen the length of keying materials to be generated.
* @return the byte array of keying materials
*/
public static byte[] prfPlus(
ByteSigner byteSigner, byte[] keyBytes, byte[] dataToSign, int keyMaterialLen) {
ByteBuffer keyMatBuffer = ByteBuffer.allocate(keyMaterialLen);
byte[] previousMac = new byte[0];
final int padLen = 1;
byte padValue = 1;
while (keyMatBuffer.remaining() > 0) {
ByteBuffer dataToSignBuffer =
ByteBuffer.allocate(previousMac.length + dataToSign.length + padLen);
dataToSignBuffer.put(previousMac).put(dataToSign).put(padValue);
previousMac = byteSigner.signBytes(keyBytes, dataToSignBuffer.array());
keyMatBuffer.put(
previousMac, 0, Math.min(previousMac.length, keyMatBuffer.remaining()));
padValue++;
}
return keyMatBuffer.array();
}
/**
* ByteSigner is an interface to be used for implementing the byte-signing for generating keys
* using {@link KeyGenerationUtils#prfPlus(ByteSigner, byte[], byte[], int)}.
*/
public interface ByteSigner {
/**
* Signs the given data using the key given.
*
* <p>Caller is responsible for providing a valid key according to their use cases.
*
* @param keyBytes the key to sign data.
* @param dataToSign the data to be signed.
* @return the signed value.
*/
byte[] signBytes(byte[] keyBytes, byte[] dataToSign);
}
}
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