/**
 *
 * Copyright 2003-2007 Jive Software, 2016-2019 Florian Schmaus.
 *
 * 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 org.jivesoftware.smack.util;

import java.security.SecureRandom;
import java.util.Random;

public class RandomUtil {

    static final ThreadLocal<SecureRandom> SECURE_RANDOM = new ThreadLocal<SecureRandom>() {
        @Override
        protected SecureRandom initialValue() {
            return new SecureRandom();
        }
    };

    /**
     * Pseudo-random number generator object for use with randomString().
     * The Random class is not considered to be cryptographically secure, so
     * only use these random Strings for low to medium security applications.
     */
    static final ThreadLocal<Random> RANDOM = new ThreadLocal<Random>() {
        @Override
        protected Random initialValue() {
            return new Random();
        }
    };

    public static int nextSecureRandomInt(int bound) {
        return SECURE_RANDOM.get().nextInt(bound);
    }

    public static int nextSecureRandomInt() {
        return SECURE_RANDOM.get().nextInt();
    }
}

/**
 *
 * Copyright 2003-2007 Jive Software, 2016-2021 Florian Schmaus.
 *
 * 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 org.jivesoftware.smack.util;

import java.security.SecureRandom;
import java.util.Random;

public class RandomUtil {

    static final ThreadLocal<SecureRandom> SECURE_RANDOM = new ThreadLocal<SecureRandom>() {
        @Override
        protected SecureRandom initialValue() {
            return new SecureRandom();
        }
    };

    /**
     * Pseudo-random number generator object for use with randomString().
     * The Random class is not considered to be cryptographically secure, so
     * only use these random Strings for low to medium security applications.
     */
    static final ThreadLocal<Random> RANDOM = new ThreadLocal<Random>() {
        @Override
        protected Random initialValue() {
            return new Random();
        }
    };

    public static int nextSecureRandomInt(int bound) {
        return SECURE_RANDOM.get().nextInt(bound);
    }

    public static int nextSecureRandomInt() {
        return SECURE_RANDOM.get().nextInt();
    }

    public static void fillWithSecureRandom(byte[] bytes) {
        SECURE_RANDOM.get().nextBytes(bytes);
    }
}

Add RandomUtil.fillWithSecureRandom(byte[])