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jeremybenn |
/* EME_PKCS1_V1_5.java --
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Copyright (C) 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.prng.IRandom;
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import gnu.java.security.prng.LimitReachedException;
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import gnu.java.security.util.PRNG;
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import java.io.ByteArrayOutputStream;
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import java.security.interfaces.RSAKey;
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import java.util.Random;
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/**
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* An implementation of the EME-PKCS1-V1.5 encoding and decoding methods.
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* <p>
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* EME-PKCS1-V1.5 is parameterised by the entity <code>k</code> which is the
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* byte count of an RSA public shared modulus.
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* <p>
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* References:
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* <ol>
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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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* </ol>
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*/
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public class EME_PKCS1_V1_5
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{
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private int k;
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private ByteArrayOutputStream baos = new ByteArrayOutputStream();
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/** Our default source of randomness. */
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private PRNG prng = PRNG.getInstance();
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private EME_PKCS1_V1_5(final int k)
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{
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super();
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this.k = k;
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}
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public static final EME_PKCS1_V1_5 getInstance(final int k)
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{
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if (k < 0)
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throw new IllegalArgumentException("k must be a positive integer");
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return new EME_PKCS1_V1_5(k);
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}
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public static final EME_PKCS1_V1_5 getInstance(final RSAKey key)
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{
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final int modBits = key.getModulus().bitLength();
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final int k = (modBits + 7) / 8;
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return EME_PKCS1_V1_5.getInstance(k);
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}
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/**
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* Generates an octet string <code>PS</code> of length <code>k - mLen -
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* 3</code> consisting of pseudo-randomly generated nonzero octets. The length
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* of <code>PS</code> will be at least eight octets.
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* <p>
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* The method then concatenates <code>PS</code>, the message <code>M</code>,
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* and other padding to form an encoded message <code>EM</code> of length
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* <code>k</code> octets as:
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* <pre>
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* EM = 0x00 || 0x02 || PS || 0x00 || M.
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* </pre>
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* <p>
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* This method uses a default PRNG to obtain the padding bytes.
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*
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* @param M the message to encode.
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* @return the encoded message <code>EM</code>.
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*/
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public byte[] encode(final byte[] M)
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{
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// a. Generate an octet string PS of length k - mLen - 3 consisting
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// of pseudo-randomly generated nonzero octets. The length of PS
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// will be at least eight octets.
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final byte[] PS = new byte[k - M.length - 3];
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// FIXME. This should be configurable, somehow.
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prng.nextBytes(PS);
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int i = 0;
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for (; i < PS.length; i++)
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{
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if (PS[i] == 0)
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PS[i] = 1;
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}
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// b. Concatenate PS, the message M, and other padding to form an
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// encoded message EM of length k octets as
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//
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// EM = 0x00 || 0x02 || PS || 0x00 || M.
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return assembleEM(PS, M);
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}
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/**
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* Similar to {@link #encode(byte[])} method, except that the source of
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* randomness to use for obtaining the padding bytes (an instance of
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* {@link IRandom}) is given as a parameter.
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*
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* @param M the message to encode.
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* @param irnd the {@link IRandom} instance to use as a source of randomness.
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* @return the encoded message <code>EM</code>.
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*/
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public byte[] encode(final byte[] M, final IRandom irnd)
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{
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final byte[] PS = new byte[k - M.length - 3];
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try
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{
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irnd.nextBytes(PS, 0, PS.length);
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int i = 0;
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outer: while (true)
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{
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for (; i < PS.length; i++)
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{
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if (PS[i] == 0x00)
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{
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System.arraycopy(PS, i + 1, PS, i, PS.length - i - 1);
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irnd.nextBytes(PS, PS.length - 1, 1);
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continue outer;
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}
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}
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break;
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}
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}
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catch (IllegalStateException x)
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{
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throw new RuntimeException("encode(): " + String.valueOf(x));
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}
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catch (LimitReachedException x)
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{
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throw new RuntimeException("encode(): " + String.valueOf(x));
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}
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return assembleEM(PS, M);
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}
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/**
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* Similar to the {@link #encode(byte[], IRandom)} method, except that the
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* source of randmoness is an instance of {@link Random}.
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*
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* @param M the message to encode.
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* @param rnd the {@link Random} instance to use as a source of randomness.
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* @return the encoded message <code>EM</code>.
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*/
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public byte[] encode(final byte[] M, final Random rnd)
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{
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final byte[] PS = new byte[k - M.length - 3];
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rnd.nextBytes(PS);
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int i = 0;
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outer: while (true)
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{
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for (; i < PS.length; i++)
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{
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if (PS[i] == 0x00)
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{
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System.arraycopy(PS, i + 1, PS, i, PS.length - i - 1);
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PS[PS.length - 1] = (byte) rnd.nextInt();
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continue outer;
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}
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}
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break;
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}
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return assembleEM(PS, M);
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}
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/**
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* Separate the encoded message <code>EM</code> into an octet string
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* <code>PS</code> consisting of nonzero octets and a message <code>M</code>
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* as:
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* <pre>
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* EM = 0x00 || 0x02 || PS || 0x00 || M.
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* </pre>
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* <p>
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* If the first octet of <code>EM</code> does not have hexadecimal value
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* <code>0x00</code>, if the second octet of <code>EM</code> does not
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* have hexadecimal value <code>0x02</code>, if there is no octet with
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* hexadecimal value <code>0x00</code> to separate <code>PS</code> from
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* <code>M</code>, or if the length of <code>PS</code> is less than
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* <code>8</code> octets, output "decryption error" and stop.
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*
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* @param EM the designated encoded message.
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* @return the decoded message <code>M</code> framed in the designated
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* <code>EM</code> value.
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* @throws IllegalArgumentException if the length of the designated entity
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* <code>EM</code> is different than <code>k</code> (the length
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* in bytes of the public shared modulus), or if any of the
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* conditions described above is detected.
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*/
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public byte[] decode(final byte[] EM)
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{
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// Separate the encoded message EM into an
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// octet string PS consisting of nonzero octets and a message M as
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//
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// EM = 0x00 || 0x02 || PS || 0x00 || M.
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//
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// If the first octet of EM does not have hexadecimal value 0x00, if
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// the second octet of EM does not have hexadecimal value 0x02, if
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// there is no octet with hexadecimal value 0x00 to separate PS from
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// M, or if the length of PS is less than 8 octets, output
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// "decryption error" and stop. (See the note below.)
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final int emLen = EM.length;
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if (emLen != k)
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throw new IllegalArgumentException("decryption error");
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if (EM[0] != 0x00)
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throw new IllegalArgumentException("decryption error");
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if (EM[1] != 0x02)
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throw new IllegalArgumentException("decryption error");
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int i = 2;
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for (; i < emLen; i++)
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{
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if (EM[i] == 0x00)
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break;
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}
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if (i >= emLen || i < 11)
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throw new IllegalArgumentException("decryption error");
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i++;
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final byte[] result = new byte[emLen - i];
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System.arraycopy(EM, i, result, 0, result.length);
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return result;
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}
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private byte[] assembleEM(final byte[] PS, final byte[] M)
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{
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// b. Concatenate PS, the message M, and other padding to form an
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// encoded message EM of length k octets as
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//
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// EM = 0x00 || 0x02 || PS || 0x00 || M.
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baos.reset();
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baos.write(0x00);
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baos.write(0x02);
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baos.write(PS, 0, PS.length);
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baos.write(0x00);
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baos.write(M, 0, M.length);
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final byte[] result = baos.toByteArray();
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baos.reset();
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return result;
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}
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}
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