我计划在我的Android应用程序中使用KeyStore，将一个AES密钥与存储在KeyStore内部的KeyPair加密。 Android KeyStore文档如下：https://developer.android.com/training/articles/keystore.html。在搜索互联网后，我找到了一个AOSP示例，我编辑后变成了这样：
/*
* Copyright (C) 2013 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.
*/
import android.annotation.TargetApi;
import android.content.Context;
import android.os.Build;
import android.security.KeyPairGeneratorSpec;
import java.io.IOException;
import java.math.BigInteger;
import java.security.GeneralSecurityException;
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.KeyStore;
import java.security.KeyStoreException;
import java.security.NoSuchAlgorithmException;
import java.security.UnrecoverableEntryException;
import java.util.Calendar;
import java.util.GregorianCalendar;
import javax.crypto.Cipher;
import javax.crypto.SecretKey;
import javax.security.auth.x500.X500Principal;
/**
* Wraps {@link SecretKey} instances using a public/private key pair stored in
* the platform {@link KeyStore}. This allows us to protect symmetric keys with
* hardware-backed crypto, if provided by the device.
* <p>
* See <a href="http://en.wikipedia.org/wiki/Key_Wrap">key wrapping</a> for more
* details.
* <p>
* Not inherently thread safe.
*
* Some explanations:
* http://nelenkov.blogspot.nl/2013/08/credential-storage-enhancements-android-43.html
*/
public class SecretKeyWrapper {
private final Cipher mCipher;
private final KeyPair mPair;
/**
* Create a wrapper using the public/private key pair with the given alias.
* If no pair with that alias exists, it will be generated.
*/
public SecretKeyWrapper(Context context, String alias)
throws GeneralSecurityException, IOException {
mCipher = Cipher.getInstance("RSA/ECB/PKCS1Padding");
final KeyStore keyStore = KeyStore.getInstance("AndroidKeyStore");
keyStore.load(null);
if (!keyStore.containsAlias(alias)) {
generateKeyPair(context, alias);
}
// Even if we just generated the key, always read it back to ensure we
// can read it successfully.
final KeyStore.PrivateKeyEntry entry = (KeyStore.PrivateKeyEntry) keyStore.getEntry(
alias, null);
mPair = new KeyPair(entry.getCertificate().getPublicKey(), entry.getPrivateKey());
}
@TargetApi(Build.VERSION_CODES.JELLY_BEAN_MR2)
private static void generateKeyPair(Context context, String alias)
throws GeneralSecurityException {
final Calendar start = new GregorianCalendar();
final Calendar end = new GregorianCalendar();
end.add(Calendar.YEAR, 100);
final KeyPairGeneratorSpec spec = new KeyPairGeneratorSpec.Builder(context)
.setAlias(alias)
.setSubject(new X500Principal("CN=" + alias))
.setSerialNumber(BigInteger.ONE)
.setStartDate(start.getTime())
.setEndDate(end.getTime())
.build();
final KeyPairGenerator gen = KeyPairGenerator.getInstance("RSA", "AndroidKeyStore");
gen.initialize(spec);
gen.generateKeyPair();
}
/**
* Wrap a {@link SecretKey} using the public key assigned to this wrapper.
* Use {@link #unwrap(byte[])} to later recover the original
* {@link SecretKey}.
*
* @return a wrapped version of the given {@link SecretKey} that can be
* safely stored on untrusted storage.
*/
public byte[] wrap(SecretKey key) throws GeneralSecurityException {
mCipher.init(Cipher.WRAP_MODE, mPair.getPublic());
return mCipher.wrap(key);
}
/**
* Unwrap a {@link SecretKey} using the private key assigned to this
* wrapper.
*
* @param blob a wrapped {@link SecretKey} as previously returned by
* {@link #wrap(SecretKey)}.
*/
public SecretKey unwrap(byte[] blob) throws GeneralSecurityException {
mCipher.init(Cipher.UNWRAP_MODE, mPair.getPrivate());
return (SecretKey) mCipher.unwrap(blob, "AES", Cipher.SECRET_KEY);
}
}
这个实现可以包装和解包一个秘密密钥，在我的情况下是一个AES密钥。
然而，这个KeyStore仅支持从4.3及以上版本。请参见Jelly Bean注释。
那么，对于低于4.3的版本，是否有类似实现的可能性呢？
提前感谢您的回复。