Java BigInteger to BigIntToPaddedByteArray(BigInteger bi, int length)

Description

Converts a BigInt (What is stored in Hydra-keystore and what our version of SSSS is using...) to a padded byte-array.

License

Open Source License

Parameter

Parameter	Description
bi	The big-int to be parsed
length	The desired length

Exception

Parameter	Description
Exception	an exception

Return

byte[] including the bigint in padded format.

Declaration

public static byte[] BigIntToPaddedByteArray(BigInteger bi, int length)
        throws Exception

Method Source Code

//package com.java2s;
/*/*from w ww.ja  v a 2s.c o  m*/
 * Copyright (C) 2012 Helsinki Institute of Physics, University of Helsinki
 * All rights reserved. See the copyright.txt in the distribution for a full 
 * listing of individual contributors.
 *    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.
 * 
 */

import java.math.BigInteger;
import java.util.Arrays;

public class Main {
    /**
     * Converts a BigInt (What is stored in Hydra-keystore and what our version of SSSS is using...) to a padded
     * byte-array. Which is compatible with JCE SecretKeySpecs
     * 
     * @param bi The big-int to be parsed
     * @param length The desired length
     * @return byte[] including the bigint in padded format.
     * @throws Exception
     */
    public static byte[] BigIntToPaddedByteArray(BigInteger bi, int length)
            throws Exception {
        byte[] biAsBytes = bi.toByteArray();
        return paddedByteArray(biAsBytes, length);
    }

    /**
     * Pads a byte-array with zeroes to a specific length. Used to make sure that reconstructed keys are extended to a
     * JCE-compatible key-size if the randomly generated key has many zero-bits in the beginning.
     * 
     * @param original The original array to be padded
     * @param length The desired length in bytes.
     * @return The key padded with zero-bits
     * @throws Exception
     */
    public static byte[] paddedByteArray(byte[] original, int length)
            throws Exception {
        // ok, it might be easier to just use this (System.arraycopy) function directly,
        // and leave the tool unused
        byte[] returnArray = new byte[length];
        int difference = length - original.length;

        // checks that the length is longer than original array
        if (difference < 0) {
            throw new Exception(
                    "New array length must be longer than original length.");
        } else {
            Arrays.fill(returnArray, (byte) 00);
            System.arraycopy(original, 0, returnArray, difference,
                    original.length);
            return returnArray;
        }
    }
}

Java BigInteger to BigIntToPaddedByteArray(BigInteger bi, int length)

Description

License

Parameter

Exception

Return

Declaration

Method Source Code

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