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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

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 * published by the Free Software Foundation.  Oracle designates this

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 * This code is distributed in the hope that it will be useful, but WITHOUT

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 * 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

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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.

     * {@code a}, or {@code b} is null.

     * 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.

     * {@code a}, or {@code b} is null.

     * 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));

    }

}