001/*
002 * nimbus-jose-jwt
003 *
004 * Copyright 2012-2016, Connect2id Ltd.
005 *
006 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use
007 * this file except in compliance with the License. You may obtain a copy of the
008 * License at
009 *
010 *    http://www.apache.org/licenses/LICENSE-2.0
011 *
012 * Unless required by applicable law or agreed to in writing, software distributed
013 * under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR
014 * CONDITIONS OF ANY KIND, either express or implied. See the License for the
015 * specific language governing permissions and limitations under the License.
016 */
017
018package com.nimbusds.jose.util;
019
020
021import java.math.BigInteger;
022
023
024/**
025 * Big integer utilities.
026 *
027 * @author Vladimir Dzhuvinov
028 * @version 2013-03-21
029 */
030public class BigIntegerUtils {
031
032
033        /**
034         * Returns a byte array representation of the specified big integer 
035         * without the sign bit.
036         * 
037         * @param bigInt The big integer to be converted. Must not be
038         *               {@code null}.
039         *
040         * @return A byte array representation of the big integer, without the
041         *         sign bit.
042         */
043        public static byte[] toBytesUnsigned(final BigInteger bigInt) {
044
045                // Copied from Apache Commons Codec 1.8
046
047                int bitlen = bigInt.bitLength();
048
049                // round bitlen
050                bitlen = ((bitlen + 7) >> 3) << 3;
051                final byte[] bigBytes = bigInt.toByteArray();
052
053                if (((bigInt.bitLength() % 8) != 0) && (((bigInt.bitLength() / 8) + 1) == (bitlen / 8))) {
054                
055                        return bigBytes;
056                
057                }
058
059                // set up params for copying everything but sign bit
060                int startSrc = 0;
061                int len = bigBytes.length;
062
063                // if bigInt is exactly byte-aligned, just skip signbit in copy
064                if ((bigInt.bitLength() % 8) == 0) {
065                        
066                        startSrc = 1;
067                        len--;
068                }
069                
070                final int startDst = bitlen / 8 - len; // to pad w/ nulls as per spec
071                final byte[] resizedBytes = new byte[bitlen / 8];
072                System.arraycopy(bigBytes, startSrc, resizedBytes, startDst, len);
073                return resizedBytes;
074        }
075
076
077        /**
078         * Prevents public instantiation.
079         */
080        private BigIntegerUtils() {
081
082        }
083}