/* * Copyright (c) 2003, 2011, Oracle and/or its affiliates. All rights reserved. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * This code is free software; you can redistribute it and/or modify it * under the terms of the GNU General Public License version 2 only, as * published by the Free Software Foundation.  Oracle designates this * particular file as subject to the "Classpath" exception as provided * by Oracle in the LICENSE file that accompanied this code. * * This code is distributed in the hope that it will be useful, but WITHOUT * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License * version 2 for more details (a copy is included in the LICENSE file that * accompanied this code). * * You should have received a copy of the GNU General Public License version * 2 along with this work; if not, write to the Free Software Foundation, * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. * * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA * or visit www.oracle.com if you need additional information or have any * questions. */ package java.security.spec; import java.math.BigInteger;import java.util.Arrays; /** * This immutable class holds the necessary values needed to represent * an elliptic curve. * * @see ECField * @see ECFieldFp * @see ECFieldF2m * * @author Valerie Peng * * @since 1.5 */public class EllipticCurve {     private final ECField field;    private final BigInteger a;    private final BigInteger b;    private final byte[] seed;     // Check coefficient c is a valid element in ECField field.    private static void checkValidity(ECField field, BigInteger c,        String cName) {        // can only perform check if field is ECFieldFp or ECFieldF2m.        if (field instanceof ECFieldFp) {            BigInteger p = ((ECFieldFp)field).getP();            if (p.compareTo(c) != 1) {                throw new IllegalArgumentException(cName + " is too large");            } else if (c.signum() < 0) {                throw new IllegalArgumentException(cName + " is negative");            }        } else if (field instanceof ECFieldF2m) {            int m = ((ECFieldF2m)field).getM();            if (c.bitLength() > m) {                throw new IllegalArgumentException(cName + " is too large");            }        }    }     /**     * Creates an elliptic curve with the specified elliptic field     * <code>field</code> and the coefficients <code>a</code> and     * <code>b</code>.     * @param field the finite field that this elliptic curve is over.     * @param a the first coefficient of this elliptic curve.     * @param b the second coefficient of this elliptic curve.     * @exception NullPointerException if <code>field</code>,     * <code>a</code>, or <code>b</code> is null.     * @exception IllegalArgumentException if <code>a</code>     * or <code>b</code> is not null and not in <code>field</code>.     */    public EllipticCurve(ECField field, BigInteger a,                         BigInteger b) {        this(field, a, b, null);    }     /**     * Creates an elliptic curve with the specified elliptic field     * <code>field</code>, the coefficients <code>a</code> and     * <code>b</code>, and the <code>seed</code> used for curve generation.     * @param field the finite field that this elliptic curve is over.     * @param a the first coefficient of this elliptic curve.     * @param b the second coefficient of this elliptic curve.     * @param seed the bytes used during curve generation for later     * validation. Contents of this array are copied to protect against     * subsequent modification.     * @exception NullPointerException if <code>field</code>,     * <code>a</code>, or <code>b</code> is null.     * @exception IllegalArgumentException if <code>a</code>     * or <code>b</code> is not null and not in <code>field</code>.     */    public EllipticCurve(ECField field, BigInteger a,                         BigInteger b, byte[] seed) {        if (field == null) {            throw new NullPointerException("field is null");        }        if (a == null) {            throw new NullPointerException("first coefficient is null");        }        if (b == null) {            throw new NullPointerException("second coefficient is null");        }        checkValidity(field, a, "first coefficient");        checkValidity(field, b, "second coefficient");        this.field = field;        this.a = a;        this.b = b;        if (seed != null) {            this.seed = seed.clone();        } else {            this.seed = null;        }    }     /**     * Returns the finite field <code>field</code> that this     * elliptic curve is over.     * @return the field <code>field</code> that this curve     * is over.     */    public ECField getField() {        return field;    }     /**     * Returns the first coefficient <code>a</code> of the     * elliptic curve.     * @return the first coefficient <code>a</code>.     */    public BigInteger getA() {        return a;    }     /**     * Returns the second coefficient <code>b</code> of the     * elliptic curve.     * @return the second coefficient <code>b</code>.     */    public BigInteger getB() {        return b;    }     /**     * Returns the seeding bytes <code>seed</code> used     * during curve generation. May be null if not specified.     * @return the seeding bytes <code>seed</code>. A new     * array is returned each time this method is called.     */    public byte[] getSeed() {        if (seed == null) return null;        else return seed.clone();    }     /**     * Compares this elliptic curve for equality with the     * specified object.     * @param obj the object to be compared.     * @return true if <code>obj</code> is an instance of     * EllipticCurve and the field, A, and B match, false otherwise.     */    public boolean equals(Object obj) {        if (this == obj) return true;        if (obj instanceof EllipticCurve) {            EllipticCurve curve = (EllipticCurve) obj;            if ((field.equals(curve.field)) &&                (a.equals(curve.a)) &&                (b.equals(curve.b))) {                    return true;            }        }        return false;    }     /**     * Returns a hash code value for this elliptic curve.     * @return a hash code value computed from the hash codes of the field, A,     * and B, as follows:     * <code>     *     (field.hashCode() << 6) + (a.hashCode() << 4) + (b.hashCode() << 2)     * </code>     */    public int hashCode() {        return (field.hashCode() << 6 +            (a.hashCode() << 4) +            (b.hashCode() << 2));    }}