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using System;
using Org.BouncyCastle.Crypto;
using Org.BouncyCastle.Security;
namespace Org.BouncyCastle.Crypto.Paddings
{
/// <summary> A padder that adds Trailing-Bit-Compliment padding to a block.
/// <p>
/// This padding pads the block out compliment of the last bit
/// of the plain text.
/// </p>
/// </summary>
public class TbcPadding
: IBlockCipherPadding
{
/// <summary> Return the name of the algorithm the cipher implements.</summary>
/// <returns> the name of the algorithm the cipher implements.
/// </returns>
public string PaddingName
{
get { return "TBC"; }
}
/// <summary> Initialise the padder.</summary>
/// <param name="random">- a SecureRandom if available.
/// </param>
public virtual void Init(SecureRandom random)
{
// nothing to do.
}
/// <summary> add the pad bytes to the passed in block, returning the
/// number of bytes added.
/// <p>
/// Note: this assumes that the last block of plain text is always
/// passed to it inside in. i.e. if inOff is zero, indicating the
/// entire block is to be overwritten with padding the value of in
/// should be the same as the last block of plain text.
/// </p>
/// </summary>
public virtual int AddPadding(byte[] input, int inOff)
{
int count = input.Length - inOff;
byte code;
if (inOff > 0)
{
code = (byte)((input[inOff - 1] & 0x01) == 0?0xff:0x00);
}
else
{
code = (byte)((input[input.Length - 1] & 0x01) == 0?0xff:0x00);
}
while (inOff < input.Length)
{
input[inOff] = code;
inOff++;
}
return count;
}
/// <summary> return the number of pad bytes present in the block.</summary>
public virtual int PadCount(byte[] input)
{
byte code = input[input.Length - 1];
int index = input.Length - 1;
while (index > 0 && input[index - 1] == code)
{
index--;
}
return input.Length - index;
}
}
}
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