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using System;
using Org.BouncyCastle.Utilities;
namespace Org.BouncyCastle.Crypto.Digests
{
/// <summary>
/// Customizable SHAKE function.
/// </summary>
public class CShakeDigest
: ShakeDigest
{
private static readonly byte[] padding = new byte[100];
private static byte[] EncodeString(byte[] str)
{
if (Arrays.IsNullOrEmpty(str))
{
return XofUtilities.LeftEncode(0L);
}
return Arrays.Concatenate(XofUtilities.LeftEncode(str.Length * 8L), str);
}
private readonly byte[] diff;
/// <summary>
/// Base constructor
/// </summary>
/// <param name="bitLength">bit length of the underlying SHAKE function, 128 or 256.</param>
/// <param name="N">the function name string, note this is reserved for use by NIST. Avoid using it if not required.</param>
/// <param name="S">the customization string - available for local use.</param>
public CShakeDigest(int bitLength, byte[] N, byte[] S)
: base(bitLength)
{
if ((N == null || N.Length == 0) && (S == null || S.Length == 0))
{
diff = null;
}
else
{
diff = Arrays.ConcatenateAll(XofUtilities.LeftEncode(rate / 8), EncodeString(N), EncodeString(S));
DiffPadAndAbsorb();
}
}
// bytepad in SP 800-185
private void DiffPadAndAbsorb()
{
int blockSize = rate / 8;
Absorb(diff, 0, diff.Length);
int delta = diff.Length % blockSize;
// only add padding if needed
if (delta != 0)
{
int required = blockSize - delta;
while (required > padding.Length)
{
Absorb(padding, 0, padding.Length);
required -= padding.Length;
}
Absorb(padding, 0, required);
}
}
public override string AlgorithmName
{
get { return "CSHAKE" + fixedOutputLength; }
}
public override int DoOutput(byte[] output, int outOff, int outLen)
{
if (diff == null)
{
return base.DoOutput(output, outOff, outLen);
}
if (!squeezing)
{
AbsorbBits(0x00, 2);
}
Squeeze(output, outOff, ((long)outLen) << 3);
return outLen;
}
public override void Reset()
{
base.Reset();
if (diff != null)
{
DiffPadAndAbsorb();
}
}
}
}
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