1/*
2 * Copyright (c) 2003, 2013, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.  Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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24 */
25package java.security.spec;
26
27import java.math.BigInteger;
28
29/**
30 * This immutable class represents a point on an elliptic curve (EC)
31 * in affine coordinates. Other coordinate systems can
32 * extend this class to represent this point in other
33 * coordinates.
34 *
35 * @author Valerie Peng
36 *
37 * @since 1.5
38 */
39public class ECPoint {
40
41    private final BigInteger x;
42    private final BigInteger y;
43
44    /**
45     * This defines the point at infinity.
46     */
47    public static final ECPoint POINT_INFINITY = new ECPoint();
48
49    // private constructor for constructing point at infinity
50    private ECPoint() {
51        this.x = null;
52        this.y = null;
53    }
54
55    /**
56     * Creates an ECPoint from the specified affine x-coordinate
57     * {@code x} and affine y-coordinate {@code y}.
58     * @param x the affine x-coordinate.
59     * @param y the affine y-coordinate.
60     * @exception NullPointerException if {@code x} or
61     * {@code y} is null.
62     */
63    public ECPoint(BigInteger x, BigInteger y) {
64        if ((x==null) || (y==null)) {
65            throw new NullPointerException("affine coordinate x or y is null");
66        }
67        this.x = x;
68        this.y = y;
69    }
70
71    /**
72     * Returns the affine x-coordinate {@code x}.
73     * Note: POINT_INFINITY has a null affine x-coordinate.
74     * @return the affine x-coordinate.
75     */
76    public BigInteger getAffineX() {
77        return x;
78    }
79
80    /**
81     * Returns the affine y-coordinate {@code y}.
82     * Note: POINT_INFINITY has a null affine y-coordinate.
83     * @return the affine y-coordinate.
84     */
85    public BigInteger getAffineY() {
86        return y;
87    }
88
89    /**
90     * Compares this elliptic curve point for equality with
91     * the specified object.
92     * @param obj the object to be compared.
93     * @return true if {@code obj} is an instance of
94     * ECPoint and the affine coordinates match, false otherwise.
95     */
96    public boolean equals(Object obj) {
97        if (this == obj) return true;
98        if (this == POINT_INFINITY) return false;
99        if (obj instanceof ECPoint) {
100            return ((x.equals(((ECPoint)obj).x)) &&
101                    (y.equals(((ECPoint)obj).y)));
102        }
103        return false;
104    }
105
106    /**
107     * Returns a hash code value for this elliptic curve point.
108     * @return a hash code value.
109     */
110    public int hashCode() {
111        if (this == POINT_INFINITY) return 0;
112        return x.hashCode() << 5 + y.hashCode();
113    }
114}
115