src/java.base/share/classes/sun/security/ssl/EphemeralKeyManager.java

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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
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 * 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).
 *
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 * 2 along with this work; if not, write to the Free Software Foundation,
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package sun.security.ssl;

import java.security.*;
import java.util.concurrent.locks.ReentrantLock;

/**
 * The "KeyManager" for ephemeral RSA keys. Ephemeral DH and ECDH keys
 * are handled by the DHCrypt and ECDHCrypt classes, respectively.
 *
 * @author  Andreas Sterbenz
 */
final class EphemeralKeyManager {

    // indices for the keys array below
    private static final int INDEX_RSA512 = 0;
    private static final int INDEX_RSA1024 = 1;

    /*
     * Current cached RSA KeyPairs. Elements are never null.
     * Indexed via the constants above.
     */
    private final EphemeralKeyPair[] keys = new EphemeralKeyPair[] {
        new EphemeralKeyPair(null),
        new EphemeralKeyPair(null),
    };

    private final ReentrantLock cachedKeysLock = new ReentrantLock();

    EphemeralKeyManager() {
        // empty
    }

    /*
     * Get a temporary RSA KeyPair.
     */
    KeyPair getRSAKeyPair(boolean export, SecureRandom random) {
        int length, index;
        if (export) {
            length = 512;
            index = INDEX_RSA512;
        } else {
            length = 1024;
            index = INDEX_RSA1024;
        }

        KeyPair kp = keys[index].getKeyPair();
        if (kp != null) {
            return kp;
        }

        cachedKeysLock.lock();
        try {
            // double check
            kp = keys[index].getKeyPair();
            if (kp != null) {
                return kp;
            }

            try {
                KeyPairGenerator kgen = KeyPairGenerator.getInstance("RSA");
                kgen.initialize(length, random);
                keys[index] = new EphemeralKeyPair(kgen.genKeyPair());
                kp = keys[index].getKeyPair();
            } catch (Exception e) {
                // ignore
            }
        } finally {
            cachedKeysLock.unlock();
        }

        return kp;
    }

    /**
     * Inner class to handle storage of ephemeral KeyPairs.
     */
    private static class EphemeralKeyPair {

        // maximum number of times a KeyPair is used
        private static final int MAX_USE = 200;

        // maximum time interval in which the keypair is used (1 hour in ms)
        private static final long USE_INTERVAL = 3600*1000;

        private KeyPair keyPair;
        private int uses;
        private final long expirationTime;

        private EphemeralKeyPair(KeyPair keyPair) {
            this.keyPair = keyPair;
            expirationTime = System.currentTimeMillis() + USE_INTERVAL;
        }

        /*
         * Check if the KeyPair can still be used.
         */
        private boolean isValid() {
            return (keyPair != null) && (uses < MAX_USE)
                   && (System.currentTimeMillis() < expirationTime);
        }

        /*
         * Return the KeyPair or null if it is invalid.
         */
        private KeyPair getKeyPair() {
            if (!isValid()) {
                keyPair = null;
                return null;
            }
            uses++;
            return keyPair;
        }
    }
}