001package com.nimbusds.jose.util; 002 003 004import java.math.BigInteger; 005 006 007/** 008 * Big integer utilities. 009 * 010 * @author Vladimir Dzhuvinov 011 * @version 2013-03-21 012 */ 013public class BigIntegerUtils { 014 015 016 /** 017 * Returns a byte array representation of the specified big integer 018 * without the sign bit. 019 * 020 * @param bigInt The big integer to be converted. Must not be 021 * {@code null}. 022 * 023 * @return A byte array representation of the big integer, without the 024 * sign bit. 025 */ 026 public static byte[] toBytesUnsigned(final BigInteger bigInt) { 027 028 // Copied from Apache Commons Codec 1.8 029 030 int bitlen = bigInt.bitLength(); 031 032 // round bitlen 033 bitlen = ((bitlen + 7) >> 3) << 3; 034 final byte[] bigBytes = bigInt.toByteArray(); 035 036 if (((bigInt.bitLength() % 8) != 0) && (((bigInt.bitLength() / 8) + 1) == (bitlen / 8))) { 037 038 return bigBytes; 039 040 } 041 042 // set up params for copying everything but sign bit 043 int startSrc = 0; 044 int len = bigBytes.length; 045 046 // if bigInt is exactly byte-aligned, just skip signbit in copy 047 if ((bigInt.bitLength() % 8) == 0) { 048 049 startSrc = 1; 050 len--; 051 } 052 053 final int startDst = bitlen / 8 - len; // to pad w/ nulls as per spec 054 final byte[] resizedBytes = new byte[bitlen / 8]; 055 System.arraycopy(bigBytes, startSrc, resizedBytes, startDst, len); 056 return resizedBytes; 057 } 058 059 060 /** 061 * Prevents public instantiation. 062 */ 063 private BigIntegerUtils() { 064 065 } 066}