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using System;
using Org.BouncyCastle.Crypto;
using Org.BouncyCastle.Crypto.Utilities;
namespace Org.BouncyCastle.Pqc.Crypto.Lms
{
public sealed class SeedDerive
{
private readonly byte[] m_I;
private readonly byte[] m_masterSeed;
private readonly IDigest m_digest;
public SeedDerive(byte[] I, byte[] masterSeed, IDigest digest)
{
m_I = I;
m_masterSeed = masterSeed;
m_digest = digest;
}
public int Q { get; set; }
public int J { get; set; }
// FIXME
public byte[] I => m_I;
// FIXME
public byte[] MasterSeed => m_masterSeed;
public byte[] DeriveSeed(bool incJ, byte[] target, int offset)
{
if (target.Length - offset < m_digest.GetDigestSize())
throw new ArgumentException("target length is less than digest size.", nameof(target));
int q = Q, j = J;
m_digest.BlockUpdate(I, 0, I.Length);
#if NETCOREAPP2_1_OR_GREATER || NETSTANDARD2_1_OR_GREATER
Span<byte> qj = stackalloc byte[7];
Pack.UInt32_To_BE((uint)q, qj);
Pack.UInt16_To_BE((ushort)j, qj[4..]);
qj[6] = 0xFF;
m_digest.BlockUpdate(qj);
#else
m_digest.Update((byte)(q >> 24));
m_digest.Update((byte)(q >> 16));
m_digest.Update((byte)(q >> 8));
m_digest.Update((byte)(q));
m_digest.Update((byte)(j >> 8));
m_digest.Update((byte)(j));
m_digest.Update(0xFF);
#endif
m_digest.BlockUpdate(m_masterSeed, 0, m_masterSeed.Length);
m_digest.DoFinal(target, offset); // Digest resets here.
if (incJ)
{
++J;
}
return target;
}
}
}
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