Back to index...

	/*
	* 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));
	}
	}

Back to index...