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/*
* Copyright 2017-2020 Rudy De Busscher (https://www.atbash.be)
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package be.atbash.ee.security.octopus.nimbus.util;
import java.math.BigInteger;
/**
* Big integer utilities.
*
* Based on code by Vladimir Dzhuvinov
*/
public final class BigIntegerUtils {
/**
* Returns a byte array representation of the specified big integer
* without the sign bit.
*
* @param bigInt The big integer to be converted. Must not be
* {@code null}.
* @return A byte array representation of the big integer, without the
* sign bit.
*/
public static byte[] toBytesUnsigned(final BigInteger bigInt) {
// Copied from Apache Commons Codec 1.8
int bitlen = bigInt.bitLength();
// round bitlen
bitlen = ((bitlen + 7) >> 3) << 3;
byte[] bigBytes = bigInt.toByteArray();
if (((bigInt.bitLength() % 8) != 0) && (((bigInt.bitLength() / 8) + 1) == (bitlen / 8))) {
return bigBytes;
}
// set up params for copying everything but sign bit
int startSrc = 0;
int len = bigBytes.length;
// if bigInt is exactly byte-aligned, just skip signbit in copy
if ((bigInt.bitLength() % 8) == 0) {
startSrc = 1;
len--;
}
int startDst = bitlen / 8 - len; // to pad w/ nulls as per spec
byte[] resizedBytes = new byte[bitlen / 8];
System.arraycopy(bigBytes, startSrc, resizedBytes, startDst, len);
return resizedBytes;
}
/**
* Prevents public instantiation.
*/
private BigIntegerUtils() {
}
}