| /* |
| * Copyright (c) 2003, 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 defines an elliptic curve (EC) |
| * characteristic 2 finite field. |
| * |
| * @see ECField |
| * |
| * @author Valerie Peng |
| * |
| * @since 1.5 |
| */ |
| public class ECFieldF2m implements ECField { |
| |
| private int m; |
| private int[] ks; |
| private BigInteger rp; |
| |
| /** |
| * Creates an elliptic curve characteristic 2 finite |
| * field which has 2^<code>m</code> elements with normal basis. |
| * @param m with 2^<code>m</code> being the number of elements. |
| * @exception IllegalArgumentException if <code>m</code> |
| * is not positive. |
| */ |
| public ECFieldF2m(int m) { |
| if (m <= 0) { |
| throw new IllegalArgumentException("m is not positive"); |
| } |
| this.m = m; |
| this.ks = null; |
| this.rp = null; |
| } |
| |
| /** |
| * Creates an elliptic curve characteristic 2 finite |
| * field which has 2^<code>m</code> elements with |
| * polynomial basis. |
| * The reduction polynomial for this field is based |
| * on <code>rp</code> whose i-th bit correspondes to |
| * the i-th coefficient of the reduction polynomial.<p> |
| * Note: A valid reduction polynomial is either a |
| * trinomial (X^<code>m</code> + X^<code>k</code> + 1 |
| * with <code>m</code> > <code>k</code> >= 1) or a |
| * pentanomial (X^<code>m</code> + X^<code>k3</code> |
| * + X^<code>k2</code> + X^<code>k1</code> + 1 with |
| * <code>m</code> > <code>k3</code> > <code>k2</code> |
| * > <code>k1</code> >= 1). |
| * @param m with 2^<code>m</code> being the number of elements. |
| * @param rp the BigInteger whose i-th bit corresponds to |
| * the i-th coefficient of the reduction polynomial. |
| * @exception NullPointerException if <code>rp</code> is null. |
| * @exception IllegalArgumentException if <code>m</code> |
| * is not positive, or <code>rp</code> does not represent |
| * a valid reduction polynomial. |
| */ |
| public ECFieldF2m(int m, BigInteger rp) { |
| // check m and rp |
| this.m = m; |
| this.rp = rp; |
| if (m <= 0) { |
| throw new IllegalArgumentException("m is not positive"); |
| } |
| int bitCount = this.rp.bitCount(); |
| if (!this.rp.testBit(0) || !this.rp.testBit(m) || |
| ((bitCount != 3) && (bitCount != 5))) { |
| throw new IllegalArgumentException |
| ("rp does not represent a valid reduction polynomial"); |
| } |
| // convert rp into ks |
| BigInteger temp = this.rp.clearBit(0).clearBit(m); |
| this.ks = new int[bitCount-2]; |
| for (int i = this.ks.length-1; i >= 0; i--) { |
| int index = temp.getLowestSetBit(); |
| this.ks[i] = index; |
| temp = temp.clearBit(index); |
| } |
| } |
| |
| /** |
| * Creates an elliptic curve characteristic 2 finite |
| * field which has 2^<code>m</code> elements with |
| * polynomial basis. The reduction polynomial for this |
| * field is based on <code>ks</code> whose content |
| * contains the order of the middle term(s) of the |
| * reduction polynomial. |
| * Note: A valid reduction polynomial is either a |
| * trinomial (X^<code>m</code> + X^<code>k</code> + 1 |
| * with <code>m</code> > <code>k</code> >= 1) or a |
| * pentanomial (X^<code>m</code> + X^<code>k3</code> |
| * + X^<code>k2</code> + X^<code>k1</code> + 1 with |
| * <code>m</code> > <code>k3</code> > <code>k2</code> |
| * > <code>k1</code> >= 1), so <code>ks</code> should |
| * have length 1 or 3. |
| * @param m with 2^<code>m</code> being the number of elements. |
| * @param ks the order of the middle term(s) of the |
| * reduction polynomial. Contents of this array are copied |
| * to protect against subsequent modification. |
| * @exception NullPointerException if <code>ks</code> is null. |
| * @exception IllegalArgumentException if<code>m</code> |
| * is not positive, or the length of <code>ks</code> |
| * is neither 1 nor 3, or values in <code>ks</code> |
| * are not between <code>m</code>-1 and 1 (inclusive) |
| * and in descending order. |
| */ |
| public ECFieldF2m(int m, int[] ks) { |
| // check m and ks |
| this.m = m; |
| this.ks = ks.clone(); |
| if (m <= 0) { |
| throw new IllegalArgumentException("m is not positive"); |
| } |
| if ((this.ks.length != 1) && (this.ks.length != 3)) { |
| throw new IllegalArgumentException |
| ("length of ks is neither 1 nor 3"); |
| } |
| for (int i = 0; i < this.ks.length; i++) { |
| if ((this.ks[i] < 1) || (this.ks[i] > m-1)) { |
| throw new IllegalArgumentException |
| ("ks["+ i + "] is out of range"); |
| } |
| if ((i != 0) && (this.ks[i] >= this.ks[i-1])) { |
| throw new IllegalArgumentException |
| ("values in ks are not in descending order"); |
| } |
| } |
| // convert ks into rp |
| this.rp = BigInteger.ONE; |
| this.rp = rp.setBit(m); |
| for (int j = 0; j < this.ks.length; j++) { |
| rp = rp.setBit(this.ks[j]); |
| } |
| } |
| |
| /** |
| * Returns the field size in bits which is <code>m</code> |
| * for this characteristic 2 finite field. |
| * @return the field size in bits. |
| */ |
| public int getFieldSize() { |
| return m; |
| } |
| |
| /** |
| * Returns the value <code>m</code> of this characteristic |
| * 2 finite field. |
| * @return <code>m</code> with 2^<code>m</code> being the |
| * number of elements. |
| */ |
| public int getM() { |
| return m; |
| } |
| |
| /** |
| * Returns a BigInteger whose i-th bit corresponds to the |
| * i-th coefficient of the reduction polynomial for polynomial |
| * basis or null for normal basis. |
| * @return a BigInteger whose i-th bit corresponds to the |
| * i-th coefficient of the reduction polynomial for polynomial |
| * basis or null for normal basis. |
| */ |
| public BigInteger getReductionPolynomial() { |
| return rp; |
| } |
| |
| /** |
| * Returns an integer array which contains the order of the |
| * middle term(s) of the reduction polynomial for polynomial |
| * basis or null for normal basis. |
| * @return an integer array which contains the order of the |
| * middle term(s) of the reduction polynomial for polynomial |
| * basis or null for normal basis. A new array is returned |
| * each time this method is called. |
| */ |
| public int[] getMidTermsOfReductionPolynomial() { |
| if (ks == null) { |
| return null; |
| } else { |
| return ks.clone(); |
| } |
| } |
| |
| /** |
| * Compares this finite field for equality with the |
| * specified object. |
| * @param obj the object to be compared. |
| * @return true if <code>obj</code> is an instance |
| * of ECFieldF2m and both <code>m</code> and the reduction |
| * polynomial match, false otherwise. |
| */ |
| public boolean equals(Object obj) { |
| if (this == obj) return true; |
| if (obj instanceof ECFieldF2m) { |
| // no need to compare rp here since ks and rp |
| // should be equivalent |
| return ((m == ((ECFieldF2m)obj).m) && |
| (Arrays.equals(ks, ((ECFieldF2m) obj).ks))); |
| } |
| return false; |
| } |
| |
| /** |
| * Returns a hash code value for this characteristic 2 |
| * finite field. |
| * @return a hash code value. |
| */ |
| public int hashCode() { |
| int value = m << 5; |
| value += (rp==null? 0:rp.hashCode()); |
| // no need to involve ks here since ks and rp |
| // should be equivalent. |
| return value; |
| } |
| } |
