KeePassDX/app/src/main/java/com/keepassdroid/compat/KeyGenParameterSpecCompat.java

/*
 * Copyright 2017 Brian Pellin.
 *
 * This file is part of KeePassDroid.
 *
 *  KeePassDroid is free software: you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation, either version 2 of the License, or
 *  (at your option) any later version.
 *
 *  KeePassDroid is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with KeePassDroid.  If not, see <http://www.gnu.org/licenses/>.
 *
 */
package com.keepassdroid.compat;


import java.lang.reflect.Constructor;
import java.lang.reflect.Method;
import java.security.spec.AlgorithmParameterSpec;

public class KeyGenParameterSpecCompat {
    private static Class builder;
    private static Constructor buildConst;
    private static Method builderBuild;
    private static Method setBlockModes;
    private static Method setUserAuthReq;
    private static Method setEncPad;

    private static boolean available;

    static {
        try {
            builder = Class.forName("android.security.keystore.KeyGenParameterSpec$Builder");
            buildConst = builder.getConstructor(String.class, int.class);
            builderBuild = builder.getMethod("build", (Class [])null);
            setBlockModes = builder.getMethod("setBlockModes", String[].class);
            setUserAuthReq = builder.getMethod("setUserAuthenticationRequired", new Class []{boolean.class});
            setEncPad = builder.getMethod("setEncryptionPaddings", String[].class);


            available = true;
        } catch (Exception e) {
            available = false;
        }
    }

    public static AlgorithmParameterSpec build(String keystoreAlias, int purpose, String blockMode,
                                        boolean userAuthReq, String encPadding) {

        if (!available) {
            return null;
        }

        try {
            Object inst = buildConst.newInstance(keystoreAlias, purpose);
            inst = setBlockModes.invoke(inst, new Object[] {new String[] {blockMode}});
            inst = setUserAuthReq.invoke(inst, userAuthReq);
            inst = setEncPad.invoke(inst, new Object[] {new String[] {encPadding}});

            return (AlgorithmParameterSpec) builderBuild.invoke(inst, null);

        } catch (Exception e) {
            return null;
        }
    }
}