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| 1 | /* | ||
| 2 | * Copyright (c) 2003, 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. | ||
| 20 | * | ||
| 21 | * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA | ||
| 22 | * or visit www.oracle.com if you need additional information or have any | ||
| 23 | * questions. | ||
| 24 | */ | ||
| 25 | package java.security.spec; | ||
| 26 | |||
| 27 | import java.math.BigInteger; | ||
| 28 | import java.util.Arrays; | ||
| 29 | |||
| 30 | /** | ||
| 31 | * This immutable class defines an elliptic curve (EC) | ||
| 32 | * characteristic 2 finite field. | ||
| 33 | * | ||
| 34 | * @see ECField | ||
| 35 | * | ||
| 36 | * @author Valerie Peng | ||
| 37 | * | ||
| 38 | * @since 1.5 | ||
| 39 | */ | ||
| 40 | public class ECFieldF2m implements ECField { | ||
| 41 | |||
| 42 | private int m; | ||
| 43 | private int[] ks; | ||
| 44 | private BigInteger rp; | ||
| 45 | |||
| 46 | /** | ||
| 47 | * Creates an elliptic curve characteristic 2 finite | ||
| 48 | * field which has 2^<code>m</code> elements with normal basis. | ||
| 49 | * @param m with 2^<code>m</code> being the number of elements. | ||
| 50 | * @exception IllegalArgumentException if <code>m</code> | ||
| 51 | * is not positive. | ||
| 52 | */ | ||
| 53 | public ECFieldF2m(int m) { | ||
| 54 | if (m <= 0) { | ||
| 55 | throw new IllegalArgumentException("m is not positive"); | ||
| 56 | } | ||
| 57 | this.m = m; | ||
| 58 | this.ks = null; | ||
| 59 | this.rp = null; | ||
| 60 | } | ||
| 61 | |||
| 62 | /** | ||
| 63 | * Creates an elliptic curve characteristic 2 finite | ||
| 64 | * field which has 2^<code>m</code> elements with | ||
| 65 | * polynomial basis. | ||
| 66 | * The reduction polynomial for this field is based | ||
| 67 | * on <code>rp</code> whose i-th bit correspondes to | ||
| 68 | * the i-th coefficient of the reduction polynomial.<p> | ||
| 69 | * Note: A valid reduction polynomial is either a | ||
| 70 | * trinomial (X^<code>m</code> + X^<code>k</code> + 1 | ||
| 71 | * with <code>m</code> > <code>k</code> >= 1) or a | ||
| 72 | * pentanomial (X^<code>m</code> + X^<code>k3</code> | ||
| 73 | * + X^<code>k2</code> + X^<code>k1</code> + 1 with | ||
| 74 | * <code>m</code> > <code>k3</code> > <code>k2</code> | ||
| 75 | * > <code>k1</code> >= 1). | ||
| 76 | * @param m with 2^<code>m</code> being the number of elements. | ||
| 77 | * @param rp the BigInteger whose i-th bit corresponds to | ||
| 78 | * the i-th coefficient of the reduction polynomial. | ||
| 79 | * @exception NullPointerException if <code>rp</code> is null. | ||
| 80 | * @exception IllegalArgumentException if <code>m</code> | ||
| 81 | * is not positive, or <code>rp</code> does not represent | ||
| 82 | * a valid reduction polynomial. | ||
| 83 | */ | ||
| 84 | public ECFieldF2m(int m, BigInteger rp) { | ||
| 85 | // check m and rp | ||
| 86 | this.m = m; | ||
| 87 | this.rp = rp; | ||
| 88 | if (m <= 0) { | ||
| 89 | throw new IllegalArgumentException("m is not positive"); | ||
| 90 | } | ||
| 91 | int bitCount = this.rp.bitCount(); | ||
| 92 | if (!this.rp.testBit(0) || !this.rp.testBit(m) || | ||
| 93 | ((bitCount != 3) && (bitCount != 5))) { | ||
| 94 | throw new IllegalArgumentException | ||
| 95 | ("rp does not represent a valid reduction polynomial"); | ||
| 96 | } | ||
| 97 | // convert rp into ks | ||
| 98 | BigInteger temp = this.rp.clearBit(0).clearBit(m); | ||
| 99 | this.ks = new int[bitCount-2]; | ||
| 100 | for (int i = this.ks.length-1; i >= 0; i--) { | ||
| 101 | int index = temp.getLowestSetBit(); | ||
| 102 | this.ks[i] = index; | ||
| 103 | temp = temp.clearBit(index); | ||
| 104 | } | ||
| 105 | } | ||
| 106 | |||
| 107 | /** | ||
| 108 | * Creates an elliptic curve characteristic 2 finite | ||
| 109 | * field which has 2^<code>m</code> elements with | ||
| 110 | * polynomial basis. The reduction polynomial for this | ||
| 111 | * field is based on <code>ks</code> whose content | ||
| 112 | * contains the order of the middle term(s) of the | ||
| 113 | * reduction polynomial. | ||
| 114 | * Note: A valid reduction polynomial is either a | ||
| 115 | * trinomial (X^<code>m</code> + X^<code>k</code> + 1 | ||
| 116 | * with <code>m</code> > <code>k</code> >= 1) or a | ||
| 117 | * pentanomial (X^<code>m</code> + X^<code>k3</code> | ||
| 118 | * + X^<code>k2</code> + X^<code>k1</code> + 1 with | ||
| 119 | * <code>m</code> > <code>k3</code> > <code>k2</code> | ||
| 120 | * > <code>k1</code> >= 1), so <code>ks</code> should | ||
| 121 | * have length 1 or 3. | ||
| 122 | * @param m with 2^<code>m</code> being the number of elements. | ||
| 123 | * @param ks the order of the middle term(s) of the | ||
| 124 | * reduction polynomial. Contents of this array are copied | ||
| 125 | * to protect against subsequent modification. | ||
| 126 | * @exception NullPointerException if <code>ks</code> is null. | ||
| 127 | * @exception IllegalArgumentException if<code>m</code> | ||
| 128 | * is not positive, or the length of <code>ks</code> | ||
| 129 | * is neither 1 nor 3, or values in <code>ks</code> | ||
| 130 | * are not between <code>m</code>-1 and 1 (inclusive) | ||
| 131 | * and in descending order. | ||
| 132 | */ | ||
| 133 | public ECFieldF2m(int m, int[] ks) { | ||
| 134 | // check m and ks | ||
| 135 | this.m = m; | ||
| 136 | this.ks = ks.clone(); | ||
| 137 | if (m <= 0) { | ||
| 138 | throw new IllegalArgumentException("m is not positive"); | ||
| 139 | } | ||
| 140 | if ((this.ks.length != 1) && (this.ks.length != 3)) { | ||
| 141 | throw new IllegalArgumentException | ||
| 142 | ("length of ks is neither 1 nor 3"); | ||
| 143 | } | ||
| 144 | for (int i = 0; i < this.ks.length; i++) { | ||
| 145 | if ((this.ks[i] < 1) || (this.ks[i] > m-1)) { | ||
| 146 | throw new IllegalArgumentException | ||
| 147 | ("ks["+ i + "] is out of range"); | ||
| 148 | } | ||
| 149 | if ((i != 0) && (this.ks[i] >= this.ks[i-1])) { | ||
| 150 | throw new IllegalArgumentException | ||
| 151 | ("values in ks are not in descending order"); | ||
| 152 | } | ||
| 153 | } | ||
| 154 | // convert ks into rp | ||
| 155 | this.rp = BigInteger.ONE; | ||
| 156 | this.rp = rp.setBit(m); | ||
| 157 | for (int j = 0; j < this.ks.length; j++) { | ||
| 158 | rp = rp.setBit(this.ks[j]); | ||
| 159 | } | ||
| 160 | } | ||
| 161 | |||
| 162 | /** | ||
| 163 | * Returns the field size in bits which is <code>m</code> | ||
| 164 | * for this characteristic 2 finite field. | ||
| 165 | * @return the field size in bits. | ||
| 166 | */ | ||
| 167 | public int getFieldSize() { | ||
| 168 | return m; | ||
| 169 | } | ||
| 170 | |||
| 171 | /** | ||
| 172 | * Returns the value <code>m</code> of this characteristic | ||
| 173 | * 2 finite field. | ||
| 174 | * @return <code>m</code> with 2^<code>m</code> being the | ||
| 175 | * number of elements. | ||
| 176 | */ | ||
| 177 | public int getM() { | ||
| 178 | return m; | ||
| 179 | } | ||
| 180 | |||
| 181 | /** | ||
| 182 | * Returns a BigInteger whose i-th bit corresponds to the | ||
| 183 | * i-th coefficient of the reduction polynomial for polynomial | ||
| 184 | * basis or null for normal basis. | ||
| 185 | * @return a BigInteger whose i-th bit corresponds to the | ||
| 186 | * i-th coefficient of the reduction polynomial for polynomial | ||
| 187 | * basis or null for normal basis. | ||
| 188 | */ | ||
| 189 | public BigInteger getReductionPolynomial() { | ||
| 190 | return rp; | ||
| 191 | } | ||
| 192 | |||
| 193 | /** | ||
| 194 | * Returns an integer array which contains the order of the | ||
| 195 | * middle term(s) of the reduction polynomial for polynomial | ||
| 196 | * basis or null for normal basis. | ||
| 197 | * @return an integer array which contains the order of the | ||
| 198 | * middle term(s) of the reduction polynomial for polynomial | ||
| 199 | * basis or null for normal basis. A new array is returned | ||
| 200 | * each time this method is called. | ||
| 201 | */ | ||
| 202 | public int[] getMidTermsOfReductionPolynomial() { | ||
| 203 | if (ks == null) { | ||
| 204 | return null; | ||
| 205 | } else { | ||
| 206 | return ks.clone(); | ||
| 207 | } | ||
| 208 | } | ||
| 209 | |||
| 210 | /** | ||
| 211 | * Compares this finite field for equality with the | ||
| 212 | * specified object. | ||
| 213 | * @param obj the object to be compared. | ||
| 214 | * @return true if <code>obj</code> is an instance | ||
| 215 | * of ECFieldF2m and both <code>m</code> and the reduction | ||
| 216 | * polynomial match, false otherwise. | ||
| 217 | */ | ||
| 218 | public boolean equals(Object obj) { | ||
| 219 | if (this == obj) return true; | ||
| 220 | if (obj instanceof ECFieldF2m) { | ||
| 221 | // no need to compare rp here since ks and rp | ||
| 222 | // should be equivalent | ||
| 223 | return ((m == ((ECFieldF2m)obj).m) && | ||
| 224 | (Arrays.equals(ks, ((ECFieldF2m) obj).ks))); | ||
| 225 | } | ||
| 226 | return false; | ||
| 227 | } | ||
| 228 | |||
| 229 | /** | ||
| 230 | * Returns a hash code value for this characteristic 2 | ||
| 231 | * finite field. | ||
| 232 | * @return a hash code value. | ||
| 233 | */ | ||
| 234 | public int hashCode() { | ||
| 235 | int value = m << 5; | ||
| 236 | value += (rp==null? 0:rp.hashCode()); | ||
| 237 | // no need to involve ks here since ks and rp | ||
| 238 | // should be equivalent. | ||
| 239 | return value; | ||
| 240 | } | ||
| 241 | } | ||