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jeremybenn |
/* RSA.java --
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Copyright (C) 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.sig.rsa;
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import gnu.java.security.Properties;
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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.PrivateKey;
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import java.security.PublicKey;
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import java.security.interfaces.RSAPrivateCrtKey;
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import java.security.interfaces.RSAPrivateKey;
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import java.security.interfaces.RSAPublicKey;
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/**
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* Utility methods related to the RSA algorithm.
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* <p>
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* References:
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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, part B.</a><br>
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* Primitive specification and supporting documentation.<br>
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* Jakob Jonsson and Burt Kaliski.</li>
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* <li><a href="http://www.ietf.org/rfc/rfc3447.txt">Public-Key Cryptography
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* Standards (PKCS) #1:</a><br>
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* RSA Cryptography Specifications Version 2.1.<br>
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* Jakob Jonsson and Burt Kaliski.</li>
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* <li><a href="http://crypto.stanford.edu/~dabo/abstracts/ssl-timing.html">
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* Remote timing attacks are practical</a><br>
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* D. Boneh and D. Brumley.</li>
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* </ol>
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*/
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public class RSA
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{
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private static final BigInteger ZERO = BigInteger.ZERO;
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private static final BigInteger ONE = BigInteger.ONE;
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/** Our default source of randomness. */
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private static final PRNG prng = PRNG.getInstance();
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/** Trivial private constructor to enforce Singleton pattern. */
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private RSA()
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{
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super();
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}
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/**
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* An implementation of the <b>RSASP</b> method: Assuming that the designated
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* RSA private key is a valid one, this method computes a <i>signature
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* representative</i> for a designated <i>message representative</i> signed
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* by the holder of the designated RSA private key.
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*
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* @param K the RSA private key.
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* @param m the <i>message representative</i>: an integer between
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* <code>0</code> and <code>n - 1</code>, where <code>n</code>
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* is the RSA <i>modulus</i>.
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* @return the <i>signature representative</i>, an integer between
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* <code>0</code> and <code>n - 1</code>, where <code>n</code>
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* is the RSA <i>modulus</i>.
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* @throws ClassCastException if <code>K</code> is not an RSA one.
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* @throws IllegalArgumentException if <code>m</code> (the <i>message
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* representative</i>) is out of range.
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*/
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public static final BigInteger sign(final PrivateKey K, final BigInteger m)
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{
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try
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{
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return RSADP((RSAPrivateKey) K, m);
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}
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catch (IllegalArgumentException x)
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{
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throw new IllegalArgumentException("message representative out of range");
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}
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}
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/**
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* An implementation of the <b>RSAVP</b> method: Assuming that the designated
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* RSA public key is a valid one, this method computes a <i>message
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* representative</i> for the designated <i>signature representative</i>
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* generated by an RSA private key, for a message intended for the holder of
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* the designated RSA public key.
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*
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* @param K the RSA public key.
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* @param s the <i>signature representative</i>, an integer between
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* <code>0</code> and <code>n - 1</code>, where <code>n</code>
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* is the RSA <i>modulus</i>.
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* @return a <i>message representative</i>: an integer between <code>0</code>
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* and <code>n - 1</code>, where <code>n</code> is the RSA
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* <i>modulus</i>.
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* @throws ClassCastException if <code>K</code> is not an RSA one.
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* @throws IllegalArgumentException if <code>s</code> (the <i>signature
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* representative</i>) is out of range.
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*/
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public static final BigInteger verify(final PublicKey K, final BigInteger s)
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{
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try
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{
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return RSAEP((RSAPublicKey) K, s);
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}
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catch (IllegalArgumentException x)
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{
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throw new IllegalArgumentException("signature representative out of range");
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}
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}
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/**
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* An implementation of the <code>RSAEP</code> algorithm.
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*
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* @param K the recipient's RSA public key.
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* @param m the message representative as an MPI.
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* @return the resulting MPI --an MPI between <code>0</code> and
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* <code>n - 1</code> (<code>n</code> being the public shared
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* modulus)-- that will eventually be padded with an appropriate
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* framing/padding scheme.
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* @throws ClassCastException if <code>K</code> is not an RSA one.
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* @throws IllegalArgumentException if <code>m</code>, the message
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* representative is not between <code>0</code> and
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* <code>n - 1</code> (<code>n</code> being the public shared
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* modulus).
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*/
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public static final BigInteger encrypt(final PublicKey K, final BigInteger m)
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{
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try
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{
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return RSAEP((RSAPublicKey) K, m);
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}
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catch (IllegalArgumentException x)
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{
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throw new IllegalArgumentException("message representative out of range");
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}
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}
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/**
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* An implementation of the <code>RSADP</code> algorithm.
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*
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* @param K the recipient's RSA private key.
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* @param c the ciphertext representative as an MPI.
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* @return the message representative, an MPI between <code>0</code> and
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* <code>n - 1</code> (<code>n</code> being the shared public
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* modulus).
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* @throws ClassCastException if <code>K</code> is not an RSA one.
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* @throws IllegalArgumentException if <code>c</code>, the ciphertext
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* representative is not between <code>0</code> and
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* <code>n - 1</code> (<code>n</code> being the shared public
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* modulus).
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*/
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public static final BigInteger decrypt(final PrivateKey K, final BigInteger c)
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{
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try
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{
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return RSADP((RSAPrivateKey) K, c);
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}
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catch (IllegalArgumentException x)
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{
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throw new IllegalArgumentException("ciphertext representative out of range");
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}
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}
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/**
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* Converts a <i>multi-precision integer</i> (MPI) <code>s</code> into an
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* octet sequence of length <code>k</code>.
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*
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* @param s the multi-precision integer to convert.
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* @param k the length of the output.
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* @return the result of the transform.
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* @exception IllegalArgumentException if the length in octets of meaningful
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* bytes of <code>s</code> is greater than <code>k</code>.
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*/
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public static final byte[] I2OSP(final BigInteger s, final int k)
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{
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byte[] result = s.toByteArray();
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if (result.length < k)
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{
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final byte[] newResult = new byte[k];
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System.arraycopy(result, 0, newResult, k - result.length, result.length);
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result = newResult;
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}
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else if (result.length > k)
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{ // leftmost extra bytes should all be 0
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final int limit = result.length - k;
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for (int i = 0; i < limit; i++)
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{
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if (result[i] != 0x00)
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throw new IllegalArgumentException("integer too large");
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}
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final byte[] newResult = new byte[k];
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System.arraycopy(result, limit, newResult, 0, k);
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result = newResult;
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}
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return result;
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}
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private static final BigInteger RSAEP(final RSAPublicKey K, final BigInteger m)
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{
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// 1. If the representative m is not between 0 and n - 1, output
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// "representative out of range" and stop.
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final BigInteger n = K.getModulus();
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if (m.compareTo(ZERO) < 0 || m.compareTo(n.subtract(ONE)) > 0)
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throw new IllegalArgumentException();
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// 2. Let c = m^e mod n.
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final BigInteger e = K.getPublicExponent();
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final BigInteger result = m.modPow(e, n);
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// 3. Output c.
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return result;
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}
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private static final BigInteger RSADP(final RSAPrivateKey K, BigInteger c)
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{
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// 1. If the representative c is not between 0 and n - 1, output
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// "representative out of range" and stop.
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final BigInteger n = K.getModulus();
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if (c.compareTo(ZERO) < 0 || c.compareTo(n.subtract(ONE)) > 0)
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throw new IllegalArgumentException();
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// 2. The representative m is computed as follows.
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BigInteger result;
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if (! (K instanceof RSAPrivateCrtKey))
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{
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// a. If the first form (n, d) of K is used, let m = c^d mod n.
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final BigInteger d = K.getPrivateExponent();
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result = c.modPow(d, n);
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}
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else
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{
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// from [3] p.13 --see class docs:
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// The RSA blinding operation calculates x = (r^e) * g mod n before
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// decryption, where r is random, e is the RSA encryption exponent, and
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// g is the ciphertext to be decrypted. x is then decrypted as normal,
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// followed by division by r, i.e. (x^e) / r mod n. Since r is random,
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// x is random and timing the decryption should not reveal information
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// about the key. Note that r should be a new random number for every
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// decryption.
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final boolean rsaBlinding = Properties.doRSABlinding();
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BigInteger r = null;
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BigInteger e = null;
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if (rsaBlinding)
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{ // pre-decryption
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r = newR(n);
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e = ((RSAPrivateCrtKey) K).getPublicExponent();
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final BigInteger x = r.modPow(e, n).multiply(c).mod(n);
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c = x;
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}
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// b. If the second form (p, q, dP, dQ, qInv) and (r_i, d_i, t_i)
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// of K is used, proceed as follows:
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final BigInteger p = ((RSAPrivateCrtKey) K).getPrimeP();
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final BigInteger q = ((RSAPrivateCrtKey) K).getPrimeQ();
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final BigInteger dP = ((RSAPrivateCrtKey) K).getPrimeExponentP();
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final BigInteger dQ = ((RSAPrivateCrtKey) K).getPrimeExponentQ();
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final BigInteger qInv = ((RSAPrivateCrtKey) K).getCrtCoefficient();
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// i. Let m_1 = c^dP mod p and m_2 = c^dQ mod q.
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final BigInteger m_1 = c.modPow(dP, p);
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final BigInteger m_2 = c.modPow(dQ, q);
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// ii. If u > 2, let m_i = c^(d_i) mod r_i, i = 3, ..., u.
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// iii. Let h = (m_1 - m_2) * qInv mod p.
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final BigInteger h = m_1.subtract(m_2).multiply(qInv).mod(p);
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// iv. Let m = m_2 + q * h.
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result = m_2.add(q.multiply(h));
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if (rsaBlinding) // post-decryption
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result = result.multiply(r.modInverse(n)).mod(n);
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}
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// 3. Output m
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return result;
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}
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/**
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* Returns a random MPI with a random bit-length of the form <code>8b</code>,
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* where <code>b</code> is in the range <code>[32..64]</code>.
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*
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* @return a random MPI whose length in bytes is between 32 and 64 inclusive.
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*/
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private static final BigInteger newR(final BigInteger N)
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{
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final int upper = (N.bitLength() + 7) / 8;
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final int lower = upper / 2;
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final byte[] bl = new byte[1];
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int b;
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do
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{
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prng.nextBytes(bl);
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b = bl[0] & 0xFF;
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}
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while (b < lower || b > upper);
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final byte[] buffer = new byte[b]; // 256-bit MPI
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prng.nextBytes(buffer);
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return new BigInteger(1, buffer);
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}
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}
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