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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code 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
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
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package sun.security.provider;

import java.io.IOException;
import java.security.AccessController;
import java.security.DrbgParameters;
import java.security.PrivilegedAction;
import java.security.SecureRandomParameters;
import java.security.SecureRandomSpi;
import java.security.Security;
import java.util.Locale;
import static java.security.DrbgParameters.Capability.*;


Implement the "SecureRandom.DRBG" algorithm. About the default "securerandom.drbg.config" value: The default value in java.security is set to "". This is because the default values of different aspects are dependent (For example, strength depends on algorithm) and if we write a full string there it will be difficult to modify one and keep all others legal. When changing default values, touch all places including: 1. comments of the security property in java.security 2. Default mech, cap, usedf set in this class 3. Default algorithm set in final implementation of each mech 4. Default strength set in AbstractDrbg, but the effective value can be smaller if an algorithm does not support it. The default value is also mentioned in the @implNote part of DrbgParameters class. 
/**
 * Implement the "SecureRandom.DRBG" algorithm.
 *
 * About the default "securerandom.drbg.config" value:
 *
 * The default value in java.security is set to "". This is because
 * the default values of different aspects are dependent (For example,
 * strength depends on algorithm) and if we write a full string there
 * it will be difficult to modify one and keep all others legal.
 *
 * When changing default values, touch all places including:
 *
 * 1. comments of the security property in java.security
 * 2. Default mech, cap, usedf set in this class
 * 3. Default algorithm set in final implementation of each mech
 * 4. Default strength set in AbstractDrbg, but the effective
 *    value can be smaller if an algorithm does not support it.
 *
 * The default value is also mentioned in the @implNote part of
 * {@link DrbgParameters} class.
 */
public final class DRBG extends SecureRandomSpi {

    private static final String PROP_NAME = "securerandom.drbg.config";

    private static final long serialVersionUID = 9L;

    private transient AbstractDrbg impl;

    
@serial
/**
     * @serial
     */
    private final MoreDrbgParameters mdp;

    public DRBG(SecureRandomParameters params) {

        // All parameters at unset status (null or -1).

        // Configurable with the "securerandom.drbg.config" security property
        String mech = null;
        Boolean usedf = null;
        String algorithm = null;

        // Default instantiate parameters also configurable with
        // "securerandom.drbg.config", and can be changed with params
        // in getInstance("drbg", params)
        int strength = -1;
        DrbgParameters.Capability cap = null;
        byte[] ps = null;

        // Not configurable with public interfaces, but is a part of
        // MoreDrbgParameters
        EntropySource es = null;
        byte[] nonce = null;

        // Can be configured with a security property

        String config = AccessController.doPrivileged((PrivilegedAction<String>)
                () -> Security.getProperty(PROP_NAME));

        if (config != null && !config.isEmpty()) {
            for (String part : config.split(",")) {
                part = part.trim();
                switch (part.toLowerCase(Locale.ROOT)) {
                    case "":
                        throw new IllegalArgumentException(
                                "aspect in " + PROP_NAME + " cannot be empty");
                    case "pr_and_reseed":
                        checkTwice(cap != null, "capability");
                        cap = PR_AND_RESEED;
                        break;
                    case "reseed_only":
                        checkTwice(cap != null, "capability");
                        cap = RESEED_ONLY;
                        break;
                    case "none":
                        checkTwice(cap != null, "capability");
                        cap = NONE;
                        break;
                    case "hash_drbg":
                    case "hmac_drbg":
                    case "ctr_drbg":
                        checkTwice(mech != null, "mechanism name");
                        mech = part;
                        break;
                    case "no_df":
                        checkTwice(usedf != null, "usedf flag");
                        usedf = false;
                        break;
                    case "use_df":
                        checkTwice(usedf != null, "usedf flag");
                        usedf = true;
                        break;
                    default:
                        // For all other parts of the property, it is
                        // either an algorithm name or a strength
                        try {
                            int tmp = Integer.parseInt(part);
                            if (tmp < 0) {
                                throw new IllegalArgumentException(
                                        "strength in " + PROP_NAME +
                                                " cannot be negative: " + part);
                            }
                            checkTwice(strength >= 0, "strength");
                            strength = tmp;
                        } catch (NumberFormatException e) {
                            checkTwice(algorithm != null, "algorithm name");
                            algorithm = part;
                        }
                }
            }
        }

        // Can be updated by params

        if (params != null) {
            // MoreDrbgParameters is used for testing.
            if (params instanceof MoreDrbgParameters) {
                MoreDrbgParameters m = (MoreDrbgParameters) params;
                params = DrbgParameters.instantiation(m.strength,
                        m.capability, m.personalizationString);

                // No need to check null for es and nonce, they are still null
                es = m.es;
                nonce = m.nonce;

                if (m.mech != null) {
                    mech = m.mech;
                }
                if (m.algorithm != null) {
                    algorithm = m.algorithm;
                }
                usedf = m.usedf;
            }
            if (params instanceof DrbgParameters.Instantiation) {
                DrbgParameters.Instantiation dp =
                        (DrbgParameters.Instantiation) params;

                // ps is still null by now
                ps = dp.getPersonalizationString();

                int tmp = dp.getStrength();
                if (tmp != -1) {
                    strength = tmp;
                }
                cap = dp.getCapability();
            } else {
                throw new IllegalArgumentException("Unsupported params: "
                        + params.getClass());
            }
        }

        // Hardcoded defaults.
        // Remember to sync with "securerandom.drbg.config" in java.security.

        if (cap == null) {
            cap = NONE;
        }
        if (mech == null) {
            mech = "Hash_DRBG";
        }
        if (usedf == null) {
            usedf = true;
        }

        mdp = new MoreDrbgParameters(
                es, mech, algorithm, nonce, usedf,
                DrbgParameters.instantiation(strength, cap, ps));

        createImpl();
    }

    private void createImpl() {
        switch (mdp.mech.toLowerCase(Locale.ROOT)) {
            case "hash_drbg":
                impl = new HashDrbg(mdp);
                break;
            case "hmac_drbg":
                impl = new HmacDrbg(mdp);
                break;
            case "ctr_drbg":
                impl = new CtrDrbg(mdp);
                break;
            default:
                throw new IllegalArgumentException("Unsupported mech: " + mdp.mech);
        }
    }

    @Override
    protected void engineSetSeed(byte[] seed) {
        impl.engineSetSeed(seed);
    }

    @Override
    protected void engineNextBytes(byte[] bytes) {
        impl.engineNextBytes(bytes);
    }

    @Override
    protected byte[] engineGenerateSeed(int numBytes) {
        return impl.engineGenerateSeed(numBytes);
    }

    @Override
    protected void engineNextBytes(
            byte[] bytes, SecureRandomParameters params) {
        impl.engineNextBytes(bytes, params);
    }

    @Override
    protected void engineReseed(SecureRandomParameters params) {
        impl.engineReseed(params);
    }

    @Override
    protected SecureRandomParameters engineGetParameters() {
        return impl.engineGetParameters();
    }

    @Override
    public String toString() {
        return impl.toString();
    }

    
Ensures an aspect is not set more than once.

Params:
  • flag – true if set more than once
  • name – the name of aspect shown in IAE
Throws:
/**
     * Ensures an aspect is not set more than once.
     *
     * @param flag true if set more than once
     * @param name the name of aspect shown in IAE
     * @throws IllegalArgumentException if it happens
     */
    private static void checkTwice(boolean flag, String name) {
        if (flag) {
            throw new IllegalArgumentException(name
                    + " cannot be provided more than once in " + PROP_NAME);
        }
    }

    private void readObject(java.io.ObjectInputStream s)
            throws IOException, ClassNotFoundException {
        s.defaultReadObject();
        if (mdp.mech == null) {
            throw new IllegalArgumentException("Input data is corrupted");
        }
        createImpl();
    }
}