1 /* 2 * Copyright (c) 1997, 2017, Oracle and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. Oracle designates this 8 * particular file as subject to the "Classpath" exception as provided 9 * by Oracle in the LICENSE file that accompanied this code. 10 * 11 * This code is distributed in the hope that it will be useful, but WITHOUT 12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 14 * version 2 for more details (a copy is included in the LICENSE file that 15 * accompanied this code). 16 * 17 * You should have received a copy of the GNU General Public License version 18 * 2 along with this work; if not, write to the Free Software Foundation, 19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 20 * 21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 22 * or visit www.oracle.com if you need additional information or have any 23 * questions. 24 */ 25 26 package com.sun.crypto.provider; 27 28 import javax.crypto.ShortBufferException; 29 import java.util.Arrays; 30 31 /** 32 * This class implements padding as specified in the PKCS#5 standard. 33 * 34 * @author Gigi Ankeny 35 * 36 * 37 * @see Padding 38 */ 39 final class PKCS5Padding implements Padding { 40 41 private int blockSize; 42 43 PKCS5Padding(int blockSize) { 44 this.blockSize = blockSize; 45 } 46 47 /** 48 * Adds the given number of padding bytes to the data input. 49 * The value of the padding bytes is determined 50 * by the specific padding mechanism that implements this 51 * interface. 52 * 53 * @param in the input buffer with the data to pad 54 * @param off the offset in <code>in</code> where the padding bytes 55 * are appended 56 * @param len the number of padding bytes to add 57 * 58 * @exception ShortBufferException if <code>in</code> is too small to hold 59 * the padding bytes 60 */ 61 public void padWithLen(byte[] in, int off, int len) 62 throws ShortBufferException 63 { 64 if (in == null) 65 return; 66 67 int idx = Math.addExact(off, len); 68 if (idx > in.length) { 69 throw new ShortBufferException("Buffer too small to hold padding"); 70 } 71 72 byte paddingOctet = (byte) (len & 0xff); 73 Arrays.fill(in, off, idx, paddingOctet); 74 return; 75 } 76 77 /** 78 * Returns the index where the padding starts. 79 * 80 * <p>Given a buffer with padded data, this method returns the 81 * index where the padding starts. 82 * 83 * @param in the buffer with the padded data 84 * @param off the offset in <code>in</code> where the padded data starts 85 * @param len the length of the padded data 86 * 87 * @return the index where the padding starts, or -1 if the input is 88 * not properly padded 89 */ 90 public int unpad(byte[] in, int off, int len) { 91 if ((in == null) || 92 (len == 0)) { // this can happen if input is really a padded buffer 93 return 0; 94 } 95 int idx = Math.addExact(off, len); 96 byte lastByte = in[idx - 1]; 97 int padValue = (int)lastByte & 0x0ff; 98 if ((padValue < 0x01) 99 || (padValue > blockSize)) { 100 return -1; 101 } 102 103 int start = idx - padValue; 104 if (start < off) { 105 return -1; 106 } 107 108 for (int i = start; i < idx; i++) { 109 if (in[i] != lastByte) { 110 return -1; 111 } 112 } 113 return start; 114 } 115 116 /** 117 * Determines how long the padding will be for a given input length. 118 * 119 * @param len the length of the data to pad 120 * 121 * @return the length of the padding 122 */ 123 public int padLength(int len) { 124 int paddingOctet = blockSize - (len % blockSize); 125 return paddingOctet; 126 } 127 }