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/*
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* Copyright (c) 2003, 2008, Oracle and/or its affiliates. All rights reserved.
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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*
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* This code is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License version 2 only, as
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* published by the Free Software Foundation. Oracle designates this
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* particular file as subject to the "Classpath" exception as provided
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* by Oracle in the LICENSE file that accompanied this code.
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*
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* This code is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* version 2 for more details (a copy is included in the LICENSE file that
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* accompanied this code).
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*
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* You should have received a copy of the GNU General Public License version
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* 2 along with this work; if not, write to the Free Software Foundation,
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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*
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* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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* or visit www.oracle.com if you need additional information or have any
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* questions.
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*/
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package sun.security.rsa;
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import java.math.BigInteger;
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import java.security.*;
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import java.security.spec.AlgorithmParameterSpec;
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import java.security.spec.RSAKeyGenParameterSpec;
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import sun.security.jca.JCAUtil;
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/**
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* RSA keypair generation. Standard algorithm, minimum key length 512 bit.
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* We generate two random primes until we find two where phi is relative
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* prime to the public exponent. Default exponent is 65537. It has only bit 0
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* and bit 4 set, which makes it particularly efficient.
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*
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* @since 1.5
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* @author Andreas Sterbenz
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*/
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public final class RSAKeyPairGenerator extends KeyPairGeneratorSpi {
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// public exponent to use
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private BigInteger publicExponent;
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// size of the key to generate, >= RSAKeyFactory.MIN_MODLEN
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private int keySize;
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// PRNG to use
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private SecureRandom random;
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public RSAKeyPairGenerator() {
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// initialize to default in case the app does not call initialize()
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initialize(1024, null);
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}
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// initialize the generator. See JCA doc
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public void initialize(int keySize, SecureRandom random) {
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// do not allow unreasonably small or large key sizes,
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// probably user error
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try {
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RSAKeyFactory.checkKeyLengths(keySize, RSAKeyGenParameterSpec.F4,
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512, 64 * 1024);
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} catch (InvalidKeyException e) {
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throw new InvalidParameterException(e.getMessage());
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}
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this.keySize = keySize;
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this.random = random;
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this.publicExponent = RSAKeyGenParameterSpec.F4;
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}
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// second initialize method. See JCA doc.
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public void initialize(AlgorithmParameterSpec params, SecureRandom random)
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throws InvalidAlgorithmParameterException {
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if (params instanceof RSAKeyGenParameterSpec == false) {
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throw new InvalidAlgorithmParameterException
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("Params must be instance of RSAKeyGenParameterSpec");
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}
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RSAKeyGenParameterSpec rsaSpec = (RSAKeyGenParameterSpec)params;
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int tmpKeySize = rsaSpec.getKeysize();
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BigInteger tmpPublicExponent = rsaSpec.getPublicExponent();
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if (tmpPublicExponent == null) {
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tmpPublicExponent = RSAKeyGenParameterSpec.F4;
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} else {
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if (tmpPublicExponent.compareTo(RSAKeyGenParameterSpec.F0) < 0) {
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throw new InvalidAlgorithmParameterException
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("Public exponent must be 3 or larger");
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}
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if (tmpPublicExponent.bitLength() > tmpKeySize) {
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throw new InvalidAlgorithmParameterException
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("Public exponent must be smaller than key size");
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}
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}
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// do not allow unreasonably large key sizes, probably user error
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try {
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RSAKeyFactory.checkKeyLengths(tmpKeySize, tmpPublicExponent,
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512, 64 * 1024);
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} catch (InvalidKeyException e) {
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throw new InvalidAlgorithmParameterException(
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"Invalid key sizes", e);
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}
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this.keySize = tmpKeySize;
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this.publicExponent = tmpPublicExponent;
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this.random = random;
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}
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// generate the keypair. See JCA doc
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public KeyPair generateKeyPair() {
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// accommodate odd key sizes in case anybody wants to use them
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int lp = (keySize + 1) >> 1;
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int lq = keySize - lp;
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if (random == null) {
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random = JCAUtil.getSecureRandom();
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}
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BigInteger e = publicExponent;
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while (true) {
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// generate two random primes of size lp/lq
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BigInteger p = BigInteger.probablePrime(lp, random);
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BigInteger q, n;
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do {
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q = BigInteger.probablePrime(lq, random);
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// convention is for p > q
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if (p.compareTo(q) < 0) {
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BigInteger tmp = p;
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p = q;
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q = tmp;
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}
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// modulus n = p * q
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n = p.multiply(q);
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// even with correctly sized p and q, there is a chance that
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// n will be one bit short. re-generate the smaller prime if so
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} while (n.bitLength() < keySize);
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// phi = (p - 1) * (q - 1) must be relative prime to e
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// otherwise RSA just won't work ;-)
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BigInteger p1 = p.subtract(BigInteger.ONE);
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BigInteger q1 = q.subtract(BigInteger.ONE);
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BigInteger phi = p1.multiply(q1);
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// generate new p and q until they work. typically
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// the first try will succeed when using F4
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if (e.gcd(phi).equals(BigInteger.ONE) == false) {
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continue;
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}
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// private exponent d is the inverse of e mod phi
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BigInteger d = e.modInverse(phi);
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// 1st prime exponent pe = d mod (p - 1)
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BigInteger pe = d.mod(p1);
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// 2nd prime exponent qe = d mod (q - 1)
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BigInteger qe = d.mod(q1);
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// crt coefficient coeff is the inverse of q mod p
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BigInteger coeff = q.modInverse(p);
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try {
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PublicKey publicKey = new RSAPublicKeyImpl(n, e);
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PrivateKey privateKey =
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new RSAPrivateCrtKeyImpl(n, e, d, p, q, pe, qe, coeff);
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return new KeyPair(publicKey, privateKey);
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} catch (InvalidKeyException exc) {
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// invalid key exception only thrown for keys < 512 bit,
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// will not happen here
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throw new RuntimeException(exc);
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}
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}
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}
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}
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