/*
* 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));
}
}