/*

 * Copyright 1997-2006 Sun Microsystems, Inc.  All Rights Reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * 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.  Sun designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Sun 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.

 *

 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,

 * CA 95054 USA or visit www.sun.com if you need additional information or

 * have any questions.

 */

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 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 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.

     *

     * <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];

        }

    }

    /**

     * Ensures that the password bytes of this key protector are

     * set to zero when there are no more references to it.

     */

    protected void finalize() {

        if (passwdBytes != null) {

            Arrays.fill(passwdBytes, (byte)0x00);

            passwdBytes = null;

        }

    }

    /*

     * 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());

        }

    }

}