| /* |
| * Copyright (C) 2018 The Android Open Source Project |
| * |
| * 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 com.android.internal.net.utils; |
| |
| import java.math.BigInteger; |
| |
| /** BigIntegerUtils provides utility methods for doing Key Exchange. */ |
| public final class BigIntegerUtils { |
| |
| /** |
| * Converts the unsigned Hex String to a positive BigInteger. |
| * |
| * @param hexString Hex representation of an unsigned value |
| * @return the argument converted to BigInteger by an unsigned conversion |
| */ |
| public static BigInteger unsignedHexStringToBigInteger(String hexString) { |
| return new BigInteger(hexString, 16); |
| } |
| |
| /** |
| * Converts the unsigned byte array to a positive BigInteger. |
| * |
| * @param byteArray byte array that represents an unsigned value |
| * @return the argument converted to BigInteger by an unsigned conversion |
| */ |
| public static BigInteger unsignedByteArrayToBigInteger(byte[] byteArray) { |
| return new BigInteger(1/** positive */, byteArray); |
| } |
| |
| /** |
| * Returns a byte array containing the unsigned representation of this BigInteger. Zero-pad on |
| * the left of byte array to desired size. |
| * |
| * @param bigInteger input BigInteger |
| * @param size size of the output byte array |
| * @return the byte array containing the unsigned representation of this BigInteger. |
| */ |
| public static byte[] bigIntegerToUnsignedByteArray(BigInteger bigInteger, int size) { |
| byte[] byteArrayWithSignBit = bigInteger.toByteArray(); |
| int len = byteArrayWithSignBit.length; |
| byte[] output = new byte[size]; |
| |
| // {@link BigInteger} provides method {@link toByteArray} that returns a byte array |
| // containing the two's-complement representation of this BigInteger (minimum number of |
| // bytes required to represent this BigInteger, including at least one sign bit). This |
| // method first remove additional byte that caused by this sign bit and zero-pad on the left |
| // of byte array to desired size. |
| if (bigInteger.bitLength() % 8 == 0) { |
| len = len - 1; |
| System.arraycopy(byteArrayWithSignBit, 1, output, size - len, len); |
| } else { |
| System.arraycopy(byteArrayWithSignBit, 0, output, size - len, len); |
| } |
| |
| return output; |
| } |
| } |