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jeremybenn |
/* RSAKeyPairGenerator.java --
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Copyright 2001, 2002, 2003, 2006 Free Software Foundation, Inc.
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This file is a part of GNU Classpath.
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GNU Classpath is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2 of the License, or (at
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your option) any later version.
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GNU Classpath is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with GNU Classpath; if not, write to the Free Software
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Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301
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USA
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Linking this library statically or dynamically with other modules is
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making a combined work based on this library. Thus, the terms and
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conditions of the GNU General Public License cover the whole
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combination.
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As a special exception, the copyright holders of this library give you
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permission to link this library with independent modules to produce an
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executable, regardless of the license terms of these independent
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modules, and to copy and distribute the resulting executable under
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terms of your choice, provided that you also meet, for each linked
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independent module, the terms and conditions of the license of that
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module. An independent module is a module which is not derived from
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or based on this library. If you modify this library, you may extend
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this exception to your version of the library, but you are not
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obligated to do so. If you do not wish to do so, delete this
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exception statement from your version. */
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package gnu.java.security.key.rsa;
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import gnu.java.security.Configuration;
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import gnu.java.security.Registry;
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import gnu.java.security.key.IKeyPairGenerator;
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import gnu.java.security.util.PRNG;
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import java.math.BigInteger;
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import java.security.KeyPair;
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import java.security.PrivateKey;
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import java.security.PublicKey;
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import java.security.SecureRandom;
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import java.security.spec.RSAKeyGenParameterSpec;
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import java.util.Map;
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import java.util.logging.Logger;
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/**
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* A key-pair generator for asymetric keys to use in conjunction with the RSA
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* scheme.
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* <p>
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* Reference:
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* <ol>
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* <li><a
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* href="http://www.cosic.esat.kuleuven.ac.be/nessie/workshop/submissions/rsa-pss.zip">
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* RSA-PSS Signature Scheme with Appendix</a>, part B. Primitive specification
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* and supporting documentation. Jakob Jonsson and Burt Kaliski. </li>
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* <li><a href="http://www.cacr.math.uwaterloo.ca/hac/">Handbook of Applied
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* Cryptography</a>, Alfred J. Menezes, Paul C. van Oorschot and Scott A.
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* Vanstone. Section 11.3 RSA and related signature schemes.</li>
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* </ol>
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*/
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public class RSAKeyPairGenerator
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implements IKeyPairGenerator
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{
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private static final Logger log = Logger.getLogger(RSAKeyPairGenerator.class.getName());
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/** The BigInteger constant 1. */
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private static final BigInteger ONE = BigInteger.ONE;
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/** The BigInteger constant 2. */
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private static final BigInteger TWO = BigInteger.valueOf(2L);
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/** Property name of the length (Integer) of the modulus of an RSA key. */
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public static final String MODULUS_LENGTH = "gnu.crypto.rsa.L";
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/**
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* Property name of an optional {@link SecureRandom} instance to use. The
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* default is to use a classloader singleton from {@link PRNG}.
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*/
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public static final String SOURCE_OF_RANDOMNESS = "gnu.crypto.rsa.prng";
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/**
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* Property name of an optional {@link RSAKeyGenParameterSpec} instance to use
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* for this generator's <code>n</code>, and <code>e</code> values. The
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* default is to generate <code>n</code> and use a fixed value for
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* <code>e</.code> (Fermat's F4 number).
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*/
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public static final String RSA_PARAMETERS = "gnu.crypto.rsa.params";
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/**
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* Property name of the preferred encoding format to use when externalizing
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* generated instance of key-pairs from this generator. The property is taken
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* to be an {@link Integer} that encapsulates an encoding format identifier.
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*/
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public static final String PREFERRED_ENCODING_FORMAT = "gnu.crypto.rsa.encoding";
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/** Default value for the modulus length. */
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private static final int DEFAULT_MODULUS_LENGTH = 1024;
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/** Default encoding format to use when none was specified. */
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private static final int DEFAULT_ENCODING_FORMAT = Registry.RAW_ENCODING_ID;
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/** The desired bit length of the modulus. */
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private int L;
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/**
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* This implementation uses, by default, Fermat's F4 number as the public
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* exponent.
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*/
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private BigInteger e = BigInteger.valueOf(65537L);
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/** The optional {@link SecureRandom} instance to use. */
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private SecureRandom rnd = null;
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/** Our default source of randomness. */
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private PRNG prng = null;
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/** Preferred encoding format of generated keys. */
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private int preferredFormat;
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// implicit 0-arguments constructor
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public String name()
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{
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return Registry.RSA_KPG;
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}
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/**
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* Configures this instance.
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*
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* @param attributes the map of name/value pairs to use.
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* @exception IllegalArgumentException if the designated MODULUS_LENGTH value
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* is less than 1024.
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*/
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public void setup(Map attributes)
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{
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if (Configuration.DEBUG)
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log.entering(this.getClass().getName(), "setup", attributes);
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// do we have a SecureRandom, or should we use our own?
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rnd = (SecureRandom) attributes.get(SOURCE_OF_RANDOMNESS);
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// are we given a set of RSA params or we shall use our own?
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RSAKeyGenParameterSpec params = (RSAKeyGenParameterSpec) attributes.get(RSA_PARAMETERS);
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// find out the modulus length
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if (params != null)
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{
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L = params.getKeysize();
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e = params.getPublicExponent();
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}
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else
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{
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Integer l = (Integer) attributes.get(MODULUS_LENGTH);
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L = (l == null ? DEFAULT_MODULUS_LENGTH : l.intValue());
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}
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if (L < 1024)
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throw new IllegalArgumentException(MODULUS_LENGTH);
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// what is the preferred encoding format
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Integer formatID = (Integer) attributes.get(PREFERRED_ENCODING_FORMAT);
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preferredFormat = formatID == null ? DEFAULT_ENCODING_FORMAT
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: formatID.intValue();
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if (Configuration.DEBUG)
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log.exiting(this.getClass().getName(), "setup");
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}
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/**
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* <p>
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* The algorithm used here is described in <i>nessie-pss-B.pdf</i> document
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* which is part of the RSA-PSS submission to NESSIE.
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* </p>
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*
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* @return an RSA keypair.
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*/
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public KeyPair generate()
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{
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if (Configuration.DEBUG)
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log.entering(this.getClass().getName(), "generate");
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BigInteger p, q, n, d;
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// 1. Generate a prime p in the interval [2**(M-1), 2**M - 1], where
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// M = CEILING(L/2), and such that GCD(p, e) = 1
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int M = (L + 1) / 2;
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BigInteger lower = TWO.pow(M - 1);
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BigInteger upper = TWO.pow(M).subtract(ONE);
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byte[] kb = new byte[(M + 7) / 8]; // enough bytes to frame M bits
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step1: while (true)
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{
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nextRandomBytes(kb);
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p = new BigInteger(1, kb).setBit(0);
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if (p.compareTo(lower) >= 0 && p.compareTo(upper) <= 0
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&& p.isProbablePrime(80) && p.gcd(e).equals(ONE))
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break step1;
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}
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// 2. Generate a prime q such that the product of p and q is an L-bit
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// number, and such that GCD(q, e) = 1
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step2: while (true)
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{
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nextRandomBytes(kb);
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q = new BigInteger(1, kb).setBit(0);
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n = p.multiply(q);
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if (n.bitLength() == L && q.isProbablePrime(80) && q.gcd(e).equals(ONE))
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break step2;
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// TODO: test for p != q
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}
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// TODO: ensure p < q
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// 3. Put n = pq. The public key is (n, e).
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// 4. Compute the parameters necessary for the private key K (see
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// Section 2.2).
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BigInteger phi = p.subtract(ONE).multiply(q.subtract(ONE));
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d = e.modInverse(phi);
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// 5. Output the public key and the private key.
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PublicKey pubK = new GnuRSAPublicKey(preferredFormat, n, e);
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PrivateKey secK = new GnuRSAPrivateKey(preferredFormat, p, q, e, d);
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KeyPair result = new KeyPair(pubK, secK);
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if (Configuration.DEBUG)
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log.exiting(this.getClass().getName(), "generate", result);
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return result;
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}
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/**
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* Fills the designated byte array with random data.
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*
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* @param buffer the byte array to fill with random data.
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*/
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private void nextRandomBytes(byte[] buffer)
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{
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if (rnd != null)
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rnd.nextBytes(buffer);
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else
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getDefaultPRNG().nextBytes(buffer);
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}
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private PRNG getDefaultPRNG()
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{
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if (prng == null)
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prng = PRNG.getInstance();
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return prng;
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}
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}
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