001 /*
002 * Copyright 2003 Sun Microsystems, Inc. All Rights Reserved.
003 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
004 *
005 * This code is free software; you can redistribute it and/or modify it
006 * under the terms of the GNU General Public License version 2 only, as
007 * published by the Free Software Foundation. Sun designates this
008 * particular file as subject to the "Classpath" exception as provided
009 * by Sun in the LICENSE file that accompanied this code.
010 *
011 * This code is distributed in the hope that it will be useful, but WITHOUT
012 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
013 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
014 * version 2 for more details (a copy is included in the LICENSE file that
015 * accompanied this code).
016 *
017 * You should have received a copy of the GNU General Public License version
018 * 2 along with this work; if not, write to the Free Software Foundation,
019 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
020 *
021 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
022 * CA 95054 USA or visit www.sun.com if you need additional information or
023 * have any questions.
024 */
025 package java.security.spec;
026
027 import java.math.BigInteger;
028
029 /**
030 * This immutable class represents a point on an elliptic curve (EC)
031 * in affine coordinates. Other coordinate systems can
032 * extend this class to represent this point in other
033 * coordinates.
034 *
035 * @author Valerie Peng
036 * @version 1.10, 05/05/07
037 *
038 * @since 1.5
039 */
040 public class ECPoint {
041
042 private final BigInteger x;
043 private final BigInteger y;
044
045 /**
046 * This defines the point at infinity.
047 */
048 public static final ECPoint POINT_INFINITY = new ECPoint();
049
050 // private constructor for constructing point at infinity
051 private ECPoint() {
052 this .x = null;
053 this .y = null;
054 }
055
056 /**
057 * Creates an ECPoint from the specified affine x-coordinate
058 * <code>x</code> and affine y-coordinate <code>y</code>.
059 * @param x the affine x-coordinate.
060 * @param y the affine y-coordinate.
061 * @exception NullPointerException if <code>x</code> or
062 * <code>y</code> is null.
063 */
064 public ECPoint(BigInteger x, BigInteger y) {
065 if ((x == null) || (y == null)) {
066 throw new NullPointerException(
067 "affine coordinate x or y is null");
068 }
069 this .x = x;
070 this .y = y;
071 }
072
073 /**
074 * Returns the affine x-coordinate <code>x</code>.
075 * Note: POINT_INFINITY has a null affine x-coordinate.
076 * @return the affine x-coordinate.
077 */
078 public BigInteger getAffineX() {
079 return x;
080 }
081
082 /**
083 * Returns the affine y-coordinate <code>y</code>.
084 * Note: POINT_INFINITY has a null affine y-coordinate.
085 * @return the affine y-coordinate.
086 */
087 public BigInteger getAffineY() {
088 return y;
089 }
090
091 /**
092 * Compares this elliptic curve point for equality with
093 * the specified object.
094 * @param obj the object to be compared.
095 * @return true if <code>obj</code> is an instance of
096 * ECPoint and the affine coordinates match, false otherwise.
097 */
098 public boolean equals(Object obj) {
099 if (this == obj)
100 return true;
101 if (this == POINT_INFINITY)
102 return false;
103 if (obj instanceof ECPoint) {
104 return ((x.equals(((ECPoint) obj).x)) && (y
105 .equals(((ECPoint) obj).y)));
106 }
107 return false;
108 }
109
110 /**
111 * Returns a hash code value for this elliptic curve point.
112 * @return a hash code value.
113 */
114 public int hashCode() {
115 if (this == POINT_INFINITY)
116 return 0;
117 return x.hashCode() << 5 + y.hashCode();
118 }
119 }
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