https://openjdk.java.net/ 
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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
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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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 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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package sun.security.provider;

import java.io.IOException;
import java.io.UnsupportedEncodingException;
import java.security.Key;
import java.security.KeyStoreException;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.security.SecureRandom;
import java.security.UnrecoverableKeyException;
import java.util.*;

import jdk.internal.ref.CleanerFactory;
import sun.security.pkcs.PKCS8Key;
import sun.security.pkcs.EncryptedPrivateKeyInfo;
import sun.security.x509.AlgorithmId;
import sun.security.util.ObjectIdentifier;
import sun.security.util.DerValue;


This is an implementation of a Sun proprietary, exportable algorithm
intended for use when protecting (or recovering the cleartext version of)
sensitive keys.
This algorithm is not intended as a general purpose cipher.
This is how the algorithm works for key protection:
p - user password
s - random salt
X - xor key
P - to-be-protected key
Y - protected key
R - what gets stored in the keystore
Step 1:
Take the user's password, append a random salt (of fixed size) to it,
and hash it: d1 = digest(p, s)
Store d1 in X.
Step 2:
Take the user's password, append the digest result from the previous step,
and hash it: dn = digest(p, dn-1).
Store dn in X (append it to the previously stored digests).
Repeat this step until the length of X matches the length of the private key
P.
Step 3:
XOR X and P, and store the result in Y: Y = X XOR P.
Step 4:
Store s, Y, and digest(p, P) in the result buffer R:
R = s + Y + digest(p, P), where "+" denotes concatenation.
(NOTE: digest(p, P) is stored in the result buffer, so that when the key is
recovered, we can check if the recovered key indeed matches the original
key.) R is stored in the keystore.
The protected key is recovered as follows:
Step1 and Step2 are the same as above, except that the salt is not randomly
generated, but taken from the result R of step 4 (the first length(s)
bytes).
Step 3 (XOR operation) yields the plaintext key.
Then concatenate the password with the recovered key, and compare with the
last length(digest(p, P)) bytes of R. If they match, the recovered key is
indeed the same key as the original key.

Author:Jan Luehe
See Also:
Since:1.2
/**
 * This is an implementation of a Sun proprietary, exportable algorithm
 * intended for use when protecting (or recovering the cleartext version of)
 * sensitive keys.
 * This algorithm is not intended as a general purpose cipher.
 *
 * This is how the algorithm works for key protection:
 *
 * p - user password
 * s - random salt
 * X - xor key
 * P - to-be-protected key
 * Y - protected key
 * R - what gets stored in the keystore
 *
 * Step 1:
 * Take the user's password, append a random salt (of fixed size) to it,
 * and hash it: d1 = digest(p, s)
 * Store d1 in X.
 *
 * Step 2:
 * Take the user's password, append the digest result from the previous step,
 * and hash it: dn = digest(p, dn-1).
 * Store dn in X (append it to the previously stored digests).
 * Repeat this step until the length of X matches the length of the private key
 * P.
 *
 * Step 3:
 * XOR X and P, and store the result in Y: Y = X XOR P.
 *
 * Step 4:
 * Store s, Y, and digest(p, P) in the result buffer R:
 * R = s + Y + digest(p, P), where "+" denotes concatenation.
 * (NOTE: digest(p, P) is stored in the result buffer, so that when the key is
 * recovered, we can check if the recovered key indeed matches the original
 * key.) R is stored in the keystore.
 *
 * The protected key is recovered as follows:
 *
 * Step1 and Step2 are the same as above, except that the salt is not randomly
 * generated, but taken from the result R of step 4 (the first length(s)
 * bytes).
 *
 * Step 3 (XOR operation) yields the plaintext key.
 *
 * Then concatenate the password with the recovered key, and compare with the
 * last length(digest(p, P)) bytes of R. If they match, the recovered key is
 * indeed the same key as the original key.
 *
 * @author Jan Luehe
 *
 *
 * @see java.security.KeyStore
 * @see JavaKeyStore
 * @see KeyTool
 *
 * @since 1.2
 */

final class KeyProtector {

    private static final int SALT_LEN = 20; // the salt length
    private static final String DIGEST_ALG = "SHA";
    private static final int DIGEST_LEN = 20;

    // defined by JavaSoft
    private static final String KEY_PROTECTOR_OID = "1.3.6.1.4.1.42.2.17.1.1";

    // The password used for protecting/recovering keys passed through this
    // key protector. We store it as a byte array, so that we can digest it.
    private byte[] passwdBytes;

    private MessageDigest md;


    
Creates an instance of this class, and initializes it with the given
password.

The password is expected to be in printable ASCII.
Normal rules for good password selection apply: at least
seven characters, mixed case, with punctuation encouraged.
Phrases or words which are easily guessed, for example by
being found in dictionaries, are bad.

/**
     * Creates an instance of this class, and initializes it with the given
     * password.
     *
     * <p>The password is expected to be in printable ASCII.
     * Normal rules for good password selection apply: at least
     * seven characters, mixed case, with punctuation encouraged.
     * Phrases or words which are easily guessed, for example by
     * being found in dictionaries, are bad.
     */
    public KeyProtector(char[] password)
        throws NoSuchAlgorithmException
    {
        int i, j;

        if (password == null) {
           throw new IllegalArgumentException("password can't be null");
        }
        md = MessageDigest.getInstance(DIGEST_ALG);
        // Convert password to byte array, so that it can be digested
        passwdBytes = new byte[password.length * 2];
        for (i=0, j=0; i<password.length; i++) {
            passwdBytes[j++] = (byte)(password[i] >> 8);
            passwdBytes[j++] = (byte)password[i];
        }
        // Use the cleaner to zero the password when no longer referenced
        final byte[] k = this.passwdBytes;
        CleanerFactory.cleaner().register(this,
                () -> java.util.Arrays.fill(k, (byte)0x00));
    }

    /*
     * Protects the given plaintext key, using the password provided at
     * construction time.
     */
    public byte[] protect(Key key) throws KeyStoreException
    {
        int i;
        int numRounds;
        byte[] digest;
        int xorOffset; // offset in xorKey where next digest will be stored
        int encrKeyOffset = 0;

        if (key == null) {
            throw new IllegalArgumentException("plaintext key can't be null");
        }

        if (!"PKCS#8".equalsIgnoreCase(key.getFormat())) {
            throw new KeyStoreException(
                "Cannot get key bytes, not PKCS#8 encoded");
        }

        byte[] plainKey = key.getEncoded();
        if (plainKey == null) {
            throw new KeyStoreException(
                "Cannot get key bytes, encoding not supported");
        }

        // Determine the number of digest rounds
        numRounds = plainKey.length / DIGEST_LEN;
        if ((plainKey.length % DIGEST_LEN) != 0)
            numRounds++;

        // Create a random salt
        byte[] salt = new byte[SALT_LEN];
        SecureRandom random = new SecureRandom();
        random.nextBytes(salt);

        // Set up the byte array which will be XORed with "plainKey"
        byte[] xorKey = new byte[plainKey.length];

        // Compute the digests, and store them in "xorKey"
        for (i = 0, xorOffset = 0, digest = salt;
             i < numRounds;
             i++, xorOffset += DIGEST_LEN) {
            md.update(passwdBytes);
            md.update(digest);
            digest = md.digest();
            md.reset();
            // Copy the digest into "xorKey"
            if (i < numRounds - 1) {
                System.arraycopy(digest, 0, xorKey, xorOffset,
                                 digest.length);
            } else {
                System.arraycopy(digest, 0, xorKey, xorOffset,
                                 xorKey.length - xorOffset);
            }
        }

        // XOR "plainKey" with "xorKey", and store the result in "tmpKey"
        byte[] tmpKey = new byte[plainKey.length];
        for (i = 0; i < tmpKey.length; i++) {
            tmpKey[i] = (byte)(plainKey[i] ^ xorKey[i]);
        }

        // Store salt and "tmpKey" in "encrKey"
        byte[] encrKey = new byte[salt.length + tmpKey.length + DIGEST_LEN];
        System.arraycopy(salt, 0, encrKey, encrKeyOffset, salt.length);
        encrKeyOffset += salt.length;
        System.arraycopy(tmpKey, 0, encrKey, encrKeyOffset, tmpKey.length);
        encrKeyOffset += tmpKey.length;

        // Append digest(password, plainKey) as an integrity check to "encrKey"
        md.update(passwdBytes);
        Arrays.fill(passwdBytes, (byte)0x00);
        passwdBytes = null;
        md.update(plainKey);
        digest = md.digest();
        md.reset();
        System.arraycopy(digest, 0, encrKey, encrKeyOffset, digest.length);

        // wrap the protected private key in a PKCS#8-style
        // EncryptedPrivateKeyInfo, and returns its encoding
        AlgorithmId encrAlg;
        try {
            encrAlg = new AlgorithmId(new ObjectIdentifier(KEY_PROTECTOR_OID));
            return new EncryptedPrivateKeyInfo(encrAlg,encrKey).getEncoded();
        } catch (IOException ioe) {
            throw new KeyStoreException(ioe.getMessage());
        }
    }

    /*
     * Recovers the plaintext version of the given key (in protected format),
     * using the password provided at construction time.
     */
    public Key recover(EncryptedPrivateKeyInfo encrInfo)
        throws UnrecoverableKeyException
    {
        int i;
        byte[] digest;
        int numRounds;
        int xorOffset; // offset in xorKey where next digest will be stored
        int encrKeyLen; // the length of the encrpyted key

        // do we support the algorithm?
        AlgorithmId encrAlg = encrInfo.getAlgorithm();
        if (!(encrAlg.getOID().toString().equals(KEY_PROTECTOR_OID))) {
            throw new UnrecoverableKeyException("Unsupported key protection "
                                                + "algorithm");
        }

        byte[] protectedKey = encrInfo.getEncryptedData();

        /*
         * Get the salt associated with this key (the first SALT_LEN bytes of
         * <code>protectedKey</code>)
         */
        byte[] salt = new byte[SALT_LEN];
        System.arraycopy(protectedKey, 0, salt, 0, SALT_LEN);

        // Determine the number of digest rounds
        encrKeyLen = protectedKey.length - SALT_LEN - DIGEST_LEN;
        numRounds = encrKeyLen / DIGEST_LEN;
        if ((encrKeyLen % DIGEST_LEN) != 0) numRounds++;

        // Get the encrypted key portion and store it in "encrKey"
        byte[] encrKey = new byte[encrKeyLen];
        System.arraycopy(protectedKey, SALT_LEN, encrKey, 0, encrKeyLen);

        // Set up the byte array which will be XORed with "encrKey"
        byte[] xorKey = new byte[encrKey.length];

        // Compute the digests, and store them in "xorKey"
        for (i = 0, xorOffset = 0, digest = salt;
             i < numRounds;
             i++, xorOffset += DIGEST_LEN) {
            md.update(passwdBytes);
            md.update(digest);
            digest = md.digest();
            md.reset();
            // Copy the digest into "xorKey"
            if (i < numRounds - 1) {
                System.arraycopy(digest, 0, xorKey, xorOffset,
                                 digest.length);
            } else {
                System.arraycopy(digest, 0, xorKey, xorOffset,
                                 xorKey.length - xorOffset);
            }
        }

        // XOR "encrKey" with "xorKey", and store the result in "plainKey"
        byte[] plainKey = new byte[encrKey.length];
        for (i = 0; i < plainKey.length; i++) {
            plainKey[i] = (byte)(encrKey[i] ^ xorKey[i]);
        }

        /*
         * Check the integrity of the recovered key by concatenating it with
         * the password, digesting the concatenation, and comparing the
         * result of the digest operation with the digest provided at the end
         * of <code>protectedKey</code>. If the two digest values are
         * different, throw an exception.
         */
        md.update(passwdBytes);
        Arrays.fill(passwdBytes, (byte)0x00);
        passwdBytes = null;
        md.update(plainKey);
        digest = md.digest();
        md.reset();
        for (i = 0; i < digest.length; i++) {
            if (digest[i] != protectedKey[SALT_LEN + encrKeyLen + i]) {
                throw new UnrecoverableKeyException("Cannot recover key");
            }
        }

        // The parseKey() method of PKCS8Key parses the key
        // algorithm and instantiates the appropriate key factory,
        // which in turn parses the key material.
        try {
            return PKCS8Key.parseKey(new DerValue(plainKey));
        } catch (IOException ioe) {
            throw new UnrecoverableKeyException(ioe.getMessage());
        }
    }
}