J. Duke | 319a3b9 | 2007-12-01 00:00:00 +0000 | [diff] [blame^] | 1 | /* |
| 2 | * Copyright 2003 Sun Microsystems, Inc. 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. Sun designates this |
| 8 | * particular file as subject to the "Classpath" exception as provided |
| 9 | * by Sun 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara, |
| 22 | * CA 95054 USA or visit www.sun.com if you need additional information or |
| 23 | * have any 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 | } |