1 package org.bouncycastle.crypto.paddings; 2 3 import java.security.SecureRandom; 4 5 import org.bouncycastle.crypto.InvalidCipherTextException; 6 7 /** 8 * A padder that adds PKCS7/PKCS5 padding to a block. 9 */ 10 public class PKCS7Padding 11 implements BlockCipherPadding 12 { 13 /** 14 * Initialise the padder. 15 * 16 * @param random - a SecureRandom if available. 17 */ 18 public void init(SecureRandom random) 19 throws IllegalArgumentException 20 { 21 // nothing to do. 22 } 23 24 /** 25 * Return the name of the algorithm the padder implements. 26 * 27 * @return the name of the algorithm the padder implements. 28 */ 29 public String getPaddingName() 30 { 31 return "PKCS7"; 32 } 33 34 /** 35 * add the pad bytes to the passed in block, returning the 36 * number of bytes added. 37 */ 38 public int addPadding( 39 byte[] in, 40 int inOff) 41 { 42 byte code = (byte)(in.length - inOff); 43 44 while (inOff < in.length) 45 { 46 in[inOff] = code; 47 inOff++; 48 } 49 50 return code; 51 } 52 53 /** 54 * return the number of pad bytes present in the block. 55 */ 56 public int padCount(byte[] in) 57 throws InvalidCipherTextException 58 { 59 int count = in[in.length - 1] & 0xff; 60 byte countAsbyte = (byte)count; 61 62 // constant time version 63 boolean failed = (count > in.length | count == 0); 64 65 for (int i = 0; i < in.length; i++) 66 { 67 failed |= (in.length - i <= count) & (in[i] != countAsbyte); 68 } 69 70 if (failed) 71 { 72 throw new InvalidCipherTextException("pad block corrupted"); 73 } 74 75 return count; 76 } 77 } 78
