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/* * Copyright (c) 2003, 2013, 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} and the coefficients {@code a} and * {@code b}. * @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 a}, or {@code b} is null. * @exception IllegalArgumentException if {@code a} * or {@code b} is not null and not in {@code field}. */ public EllipticCurve(ECField field, BigInteger a, BigInteger b) { this(field, a, b, null); } /** * Creates an elliptic curve with the specified elliptic field * {@code field}, the coefficients {@code a} and * {@code b}, and the {@code seed} 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 a}, or {@code b} is null. * @exception IllegalArgumentException if {@code a} * or {@code b} is not null and not in {@code field}. */ 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} that this * elliptic curve is over. * @return the field {@code field} that this curve * is over. */ public ECField getField() { return field; } /** * Returns the first coefficient {@code a} of the * elliptic curve. * @return the first coefficient {@code a}. */ public BigInteger getA() { return a; } /** * Returns the second coefficient {@code b} of the * elliptic curve. * @return the second coefficient {@code b}. */ public BigInteger getB() { return b; } /** * Returns the seeding bytes {@code seed} used * during curve generation. May be null if not specified. * @return the seeding bytes {@code seed}. 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} 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: * <pre>{@code * (field.hashCode() << 6) + (a.hashCode() << 4) + (b.hashCode() << 2) * }</pre> */ public int hashCode() { return (field.hashCode() << 6 + (a.hashCode() << 4) + (b.hashCode() << 2)); } }