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/*
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* Copyright (c) 2003, 2006, 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 java.security.spec;
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import java.math.BigInteger;
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import java.util.Arrays;
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/**
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* This immutable class holds the necessary values needed to represent
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* an elliptic curve.
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*
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* @see ECField
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* @see ECFieldFp
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* @see ECFieldF2m
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*
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* @author Valerie Peng
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*
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* @since 1.5
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*/
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public class EllipticCurve {
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private final ECField field;
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private final BigInteger a;
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private final BigInteger b;
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private final byte[] seed;
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// Check coefficient c is a valid element in ECField field.
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private static void checkValidity(ECField field, BigInteger c,
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String cName) {
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// can only perform check if field is ECFieldFp or ECFieldF2m.
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if (field instanceof ECFieldFp) {
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BigInteger p = ((ECFieldFp)field).getP();
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if (p.compareTo(c) != 1) {
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throw new IllegalArgumentException(cName + " is too large");
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} else if (c.signum() < 0) {
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throw new IllegalArgumentException(cName + " is negative");
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}
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} else if (field instanceof ECFieldF2m) {
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int m = ((ECFieldF2m)field).getM();
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if (c.bitLength() > m) {
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throw new IllegalArgumentException(cName + " is too large");
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}
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}
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}
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/**
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* Creates an elliptic curve with the specified elliptic field
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* <code>field</code> and the coefficients <code>a</code> and
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* <code>b</code>.
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* @param field the finite field that this elliptic curve is over.
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* @param a the first coefficient of this elliptic curve.
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* @param b the second coefficient of this elliptic curve.
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* @exception NullPointerException if <code>field</code>,
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* <code>a</code>, or <code>b</code> is null.
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* @exception IllegalArgumentException if <code>a</code>
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* or <code>b</code> is not null and not in <code>field</code>.
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*/
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public EllipticCurve(ECField field, BigInteger a,
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BigInteger b) {
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this(field, a, b, null);
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}
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/**
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* Creates an elliptic curve with the specified elliptic field
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* <code>field</code>, the coefficients <code>a</code> and
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* <code>b</code>, and the <code>seed</code> used for curve generation.
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* @param field the finite field that this elliptic curve is over.
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* @param a the first coefficient of this elliptic curve.
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* @param b the second coefficient of this elliptic curve.
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* @param seed the bytes used during curve generation for later
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* validation. Contents of this array are copied to protect against
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* subsequent modification.
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* @exception NullPointerException if <code>field</code>,
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* <code>a</code>, or <code>b</code> is null.
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* @exception IllegalArgumentException if <code>a</code>
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* or <code>b</code> is not null and not in <code>field</code>.
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*/
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public EllipticCurve(ECField field, BigInteger a,
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BigInteger b, byte[] seed) {
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if (field == null) {
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throw new NullPointerException("field is null");
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}
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if (a == null) {
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throw new NullPointerException("first coefficient is null");
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}
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if (b == null) {
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throw new NullPointerException("second coefficient is null");
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}
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checkValidity(field, a, "first coefficient");
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checkValidity(field, b, "second coefficient");
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this.field = field;
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this.a = a;
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this.b = b;
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if (seed != null) {
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this.seed = seed.clone();
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} else {
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this.seed = null;
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}
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}
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/**
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* Returns the finite field <code>field</code> that this
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* elliptic curve is over.
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* @return the field <code>field</code> that this curve
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* is over.
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*/
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public ECField getField() {
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return field;
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}
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/**
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* Returns the first coefficient <code>a</code> of the
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* elliptic curve.
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* @return the first coefficient <code>a</code>.
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*/
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public BigInteger getA() {
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return a;
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}
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/**
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* Returns the second coefficient <code>b</code> of the
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* elliptic curve.
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* @return the second coefficient <code>b</code>.
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*/
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public BigInteger getB() {
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return b;
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}
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/**
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* Returns the seeding bytes <code>seed</code> used
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* during curve generation. May be null if not specified.
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* @return the seeding bytes <code>seed</code>. A new
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* array is returned each time this method is called.
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*/
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public byte[] getSeed() {
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if (seed == null) return null;
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else return seed.clone();
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}
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/**
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* Compares this elliptic curve for equality with the
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* specified object.
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* @param obj the object to be compared.
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* @return true if <code>obj</code> is an instance of
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* EllipticCurve and the field, A, B, and seeding bytes
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* match, false otherwise.
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*/
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public boolean equals(Object obj) {
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if (this == obj) return true;
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if (obj instanceof EllipticCurve) {
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EllipticCurve curve = (EllipticCurve) obj;
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if ((field.equals(curve.field)) &&
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(a.equals(curve.a)) &&
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(b.equals(curve.b)) &&
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(Arrays.equals(seed, curve.seed))) {
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return true;
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}
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}
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return false;
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}
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/**
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* Returns a hash code value for this elliptic curve.
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* @return a hash code value.
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*/
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public int hashCode() {
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return (field.hashCode() << 6 +
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(a.hashCode() << 4) +
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(b.hashCode() << 2) +
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(seed==null? 0:seed.length));
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}
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}
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