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using Org.BouncyCastle.Crypto.Digests;
using Org.BouncyCastle.Crypto.Parameters;
using Org.BouncyCastle.Utilities;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace Org.BouncyCastle.Crypto.Macs
{
public class KMac : IMac, IXof
{
private static readonly byte[] padding = new byte[100];
private readonly CSHAKEDigest cshake;
private readonly int bitLength;
private readonly int outputLength;
private byte[] key;
private bool initialised;
private bool firstOutput;
public KMac(int bitLength, byte[] S)
{
this.cshake = new CSHAKEDigest(bitLength, Encoding.ASCII.GetBytes("KMAC"),S);
this.bitLength = bitLength;
this.outputLength = bitLength * 2 / 8;
}
public string AlgorithmName => "KMAC" + cshake.AlgorithmName.Substring(6);
public void BlockUpdate(byte[] input, int inOff, int len)
{
if (!initialised)
{
throw new InvalidOperationException("KMAC not initialized");
}
cshake.BlockUpdate(input, inOff, len);
}
public int DoFinal(byte[] output, int outOff)
{
if (firstOutput)
{
if (!initialised)
{
throw new InvalidOperationException("KMAC not initialized");
}
byte[] encOut = XofUtils.rightEncode(GetMacSize() * 8);
cshake.BlockUpdate(encOut, 0, encOut.Length);
}
int rv = cshake.DoFinal(output, outOff, GetMacSize());
Reset();
return rv;
}
public int DoFinal(byte[] output, int outOff, int outLen)
{
if (firstOutput)
{
if (!initialised)
{
throw new InvalidOperationException("KMAC not initialized");
}
byte[] encOut = XofUtils.rightEncode(outLen * 8);
cshake.BlockUpdate(encOut, 0, encOut.Length);
}
int rv = cshake.DoFinal(output, outOff, outLen);
Reset();
return rv;
}
public int DoOutput(byte[] output, int outOff, int outLen)
{
if (firstOutput)
{
if (!initialised)
{
throw new InvalidOperationException("KMAC not initialized");
}
byte[] encOut = XofUtils.rightEncode(0);
cshake.BlockUpdate(encOut, 0, encOut.Length);
firstOutput = false;
}
return cshake.DoOutput(output, outOff, outLen);
}
public int GetByteLength()
{
return cshake.GetByteLength();
}
public int GetDigestSize()
{
return outputLength;
}
public int GetMacSize()
{
return outputLength;
}
public void Init(ICipherParameters parameters)
{
KeyParameter kParam = (KeyParameter)parameters;
this.key = Arrays.Clone(kParam.GetKey());
this.initialised = true;
Reset();
}
public void Reset()
{
cshake.Reset();
if (key != null)
{
if (bitLength == 128)
{
bytePad(key, 168);
}
else
{
bytePad(key, 136);
}
}
firstOutput = true;
}
private void bytePad(byte[] X, int w)
{
byte[] bytes = XofUtils.leftEncode(w);
BlockUpdate(bytes, 0, bytes.Length);
byte[] encX = encode(X);
BlockUpdate(encX, 0, encX.Length);
int required = w - ((bytes.Length + encX.Length) % w);
if (required > 0 && required != w)
{
while (required > padding.Length)
{
BlockUpdate(padding, 0, padding.Length);
required -= padding.Length;
}
BlockUpdate(padding, 0, required);
}
}
private static byte[] encode(byte[] X)
{
return Arrays.Concatenate(XofUtils.leftEncode(X.Length * 8), X);
}
public void Update(byte input)
{
if (!initialised)
{
throw new InvalidOperationException("KMAC not initialized");
}
cshake.Update(input);
}
}
}
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