content: /*
   * 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));
      }
  }
  