package org.bouncycastle.crypto.paddings;
import java.security.SecureRandom;
import org.bouncycastle.crypto.InvalidCipherTextException;
/**
* A padder that adds PKCS7/PKCS5 padding to a block.
*/
public class PKCS7Padding
implements BlockCipherPadding
{
/**
* Initialise the padder.
*
* @param random - a SecureRandom if available.
*/
public void init(SecureRandom random)
throws IllegalArgumentException
{
// nothing to do.
}
/**
* Return the name of the algorithm the padder implements.
*
* @return the name of the algorithm the padder implements.
*/
public String getPaddingName()
{
return "PKCS7";
}
/**
* add the pad bytes to the passed in block, returning the
* number of bytes added.
*/
public int addPadding(
byte[] in,
int inOff)
{
byte code = (byte)(in.length - inOff);
while (inOff < in.length)
{
in[inOff] = code;
inOff++;
}
return code;
}
/**
* return the number of pad bytes present in the block.
*/
public int padCount(byte[] in)
throws InvalidCipherTextException
{
int count = in[in.length - 1] & 0xff;
if (count > in.length || count == 0)
{
throw new InvalidCipherTextException("pad block corrupted");
}
for (int i = 1; i <= count; i++)
{
if (in[in.length - i] != count)
{
throw new InvalidCipherTextException("pad block corrupted");
}
}
return count;
}
}