/*
* 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());
}
}
}