1 /*
2 * Copyright (c) 2003, 2017, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation. Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 */
25
26 package sun.security.rsa;
27
28 import java.math.BigInteger;
29
30 import java.security.*;
31 import java.security.spec.AlgorithmParameterSpec;
32 import java.security.spec.RSAKeyGenParameterSpec;
33
34 import sun.security.jca.JCAUtil;
35 import static sun.security.util.SecurityProviderConstants.DEF_RSA_KEY_SIZE;
36
37 /**
38 * RSA keypair generation. Standard algorithm, minimum key length 512 bit.
39 * We generate two random primes until we find two where phi is relative
40 * prime to the public exponent. Default exponent is 65537. It has only bit 0
41 * and bit 4 set, which makes it particularly efficient.
42 *
43 * @since 1.5
44 * @author Andreas Sterbenz
45 */
46 public final class RSAKeyPairGenerator extends KeyPairGeneratorSpi {
47
48 // public exponent to use
49 private BigInteger publicExponent;
50
51 // size of the key to generate, >= RSAKeyFactory.MIN_MODLEN
52 private int keySize;
53
54 // PRNG to use
55 private SecureRandom random;
56
57 public RSAKeyPairGenerator() {
58 // initialize to default in case the app does not call initialize()
59 initialize(DEF_RSA_KEY_SIZE, null);
60 }
61
62 // initialize the generator. See JCA doc
63 public void initialize(int keySize, SecureRandom random) {
64
65 // do not allow unreasonably small or large key sizes,
66 // probably user error
67 try {
68 RSAKeyFactory.checkKeyLengths(keySize, RSAKeyGenParameterSpec.F4,
69 512, 64 * 1024);
70 } catch (InvalidKeyException e) {
71 throw new InvalidParameterException(e.getMessage());
72 }
73
74 this.keySize = keySize;
75 this.random = random;
76 this.publicExponent = RSAKeyGenParameterSpec.F4;
77 }
78
79 // second initialize method. See JCA doc.
80 public void initialize(AlgorithmParameterSpec params, SecureRandom random)
81 throws InvalidAlgorithmParameterException {
82
83 if (params instanceof RSAKeyGenParameterSpec == false) {
84 throw new InvalidAlgorithmParameterException
85 ("Params must be instance of RSAKeyGenParameterSpec");
86 }
87
88 RSAKeyGenParameterSpec rsaSpec = (RSAKeyGenParameterSpec)params;
89 int tmpKeySize = rsaSpec.getKeysize();
90 BigInteger tmpPublicExponent = rsaSpec.getPublicExponent();
91
92 if (tmpPublicExponent == null) {
93 tmpPublicExponent = RSAKeyGenParameterSpec.F4;
94 } else {
95 if (tmpPublicExponent.compareTo(RSAKeyGenParameterSpec.F0) < 0) {
96 throw new InvalidAlgorithmParameterException
97 ("Public exponent must be 3 or larger");
98 }
99 if (tmpPublicExponent.bitLength() > tmpKeySize) {
100 throw new InvalidAlgorithmParameterException
101 ("Public exponent must be smaller than key size");
102 }
103 }
104
105 // do not allow unreasonably large key sizes, probably user error
106 try {
107 RSAKeyFactory.checkKeyLengths(tmpKeySize, tmpPublicExponent,
108 512, 64 * 1024);
109 } catch (InvalidKeyException e) {
110 throw new InvalidAlgorithmParameterException(
111 "Invalid key sizes", e);
112 }
113
114 this.keySize = tmpKeySize;
115 this.publicExponent = tmpPublicExponent;
116 this.random = random;
117 }
118
119 // generate the keypair. See JCA doc
120 public KeyPair generateKeyPair() {
121 // accommodate odd key sizes in case anybody wants to use them
122 int lp = (keySize + 1) >> 1;
123 int lq = keySize - lp;
124 if (random == null) {
125 random = JCAUtil.getSecureRandom();
126 }
127 BigInteger e = publicExponent;
128 while (true) {
129 // generate two random primes of size lp/lq
130 BigInteger p = BigInteger.probablePrime(lp, random);
131 BigInteger q, n;
132 do {
133 q = BigInteger.probablePrime(lq, random);
134 // convention is for p > q
135 if (p.compareTo(q) < 0) {
136 BigInteger tmp = p;
137 p = q;
138 q = tmp;
139 }
140 // modulus n = p * q
141 n = p.multiply(q);
142 // even with correctly sized p and q, there is a chance that
143 // n will be one bit short. re-generate the smaller prime if so
144 } while (n.bitLength() < keySize);
145
146 // phi = (p - 1) * (q - 1) must be relative prime to e
147 // otherwise RSA just won't work ;-)
148 BigInteger p1 = p.subtract(BigInteger.ONE);
149 BigInteger q1 = q.subtract(BigInteger.ONE);
150 BigInteger phi = p1.multiply(q1);
151 // generate new p and q until they work. typically
152 // the first try will succeed when using F4
153 if (e.gcd(phi).equals(BigInteger.ONE) == false) {
154 continue;
155 }
156
157 // private exponent d is the inverse of e mod phi
158 BigInteger d = e.modInverse(phi);
159
160 // 1st prime exponent pe = d mod (p - 1)
161 BigInteger pe = d.mod(p1);
162 // 2nd prime exponent qe = d mod (q - 1)
163 BigInteger qe = d.mod(q1);
164
165 // crt coefficient coeff is the inverse of q mod p
166 BigInteger coeff = q.modInverse(p);
167
168 try {
169 PublicKey publicKey = new RSAPublicKeyImpl(n, e);
170 PrivateKey privateKey =
171 new RSAPrivateCrtKeyImpl(n, e, d, p, q, pe, qe, coeff);
172 return new KeyPair(publicKey, privateKey);
173 } catch (InvalidKeyException exc) {
174 // invalid key exception only thrown for keys < 512 bit,
175 // will not happen here
176 throw new RuntimeException(exc);
177 }
178 }
179 }
180
181 }