/// <summary>
/// Calculates the authpath and root for tree in layer h which starts with seed[h]
/// </summary>
///
/// <param name="NextStack">Stack used for the treehash instance created by this method</param>
/// <param name="Seed">Starting seeds</param>
/// <param name="H">Actual layer</param>
///
/// <returns>An initialized GMSSRootCalc</returns>
private GMSSRootCalc GenerateNextAuthpathAndRoot(List<byte[]> NextStack, byte[] Seed, int H)
{
byte[] OTSseed = new byte[_numLayer];
WinternitzOTSignature ots;
// data structure that constructs the whole tree and stores the initial values for treehash, Auth and retain
GMSSRootCalc treeToConstruct = new GMSSRootCalc(_heightOfTrees[H], _K[H], GetDigest(_msgDigestType));
treeToConstruct.Initialize(NextStack);
int seedForTreehashIndex = 3;
int count = 0;
// update the tree 2^(H) times, from the first to the last leaf
for (int i = 0; i < (1 << _heightOfTrees[H]); i++)
{
// initialize the seeds for the leaf generation with index 3 * 2^h
if (i == seedForTreehashIndex && count < _heightOfTrees[H] - _K[H])
{
treeToConstruct.InitializeTreehashSeed(Seed, count);
seedForTreehashIndex *= 2;
count++;
}
OTSseed = _gmssRand.NextSeed(Seed);
ots = new WinternitzOTSignature(OTSseed, GetDigest(_msgDigestType), _otsIndex[H]);
treeToConstruct.Update(ots.GetPublicKey());
}
if (treeToConstruct.IsFinished())
return treeToConstruct;
return null;
}
/// <summary>
/// Calculates the authpath for tree in layer h which starts with seed[h] additionally computes the rootSignature of underlaying root
/// </summary>
///
/// <param name="LowerRoot">Stores the root of the lower tree</param>
/// <param name="CurrentStack">Stack used for the treehash instance created by this method</param>
/// <param name="Seed">Starting seeds</param>
/// <param name="H">Actual layer</param>
/// <returns>An initialized GMSSRootCalc</returns>
private GMSSRootCalc GenerateCurrentAuthpathAndRoot(byte[] LowerRoot, List<byte[]> CurrentStack, byte[] Seed, int H)
{
byte[] help = new byte[_mdLength];
byte[] OTSseed = new byte[_mdLength];
OTSseed = _gmssRand.NextSeed(Seed);
WinternitzOTSignature ots;
// data structure that constructs the whole tree and stores the initial values for treehash, Auth and retain
GMSSRootCalc treeToConstruct = new GMSSRootCalc(_heightOfTrees[H], _K[H], GetDigest(_msgDigestType));
treeToConstruct.Initialize(CurrentStack);
// generate the first leaf
if (H == _numLayer - 1)
{
ots = new WinternitzOTSignature(OTSseed, GetDigest(_msgDigestType), _otsIndex[H]);
help = ots.GetPublicKey();
}
else
{
// for all layers except the lowest, generate the signature of the underlying root
// and reuse this signature to compute the first leaf of acual layer more efficiently (by verifiing the signature)
ots = new WinternitzOTSignature(OTSseed, GetDigest(_msgDigestType), _otsIndex[H]);
_currentRootSigs[H] = ots.GetSignature(LowerRoot);
WinternitzOTSVerify otsver = new WinternitzOTSVerify(GetDigest(_msgDigestType), _otsIndex[H]);
help = otsver.Verify(LowerRoot, _currentRootSigs[H]);
}
// update the tree with the first leaf
treeToConstruct.Update(help);
int seedForTreehashIndex = 3;
int count = 0;
// update the tree 2^(H) - 1 times, from the second to the last leaf
for (int i = 1; i < (1 << _heightOfTrees[H]); i++)
{
// initialize the seeds for the leaf generation with index 3 * 2^h
if (i == seedForTreehashIndex && count < _heightOfTrees[H] - _K[H])
{
treeToConstruct.InitializeTreehashSeed(Seed, count);
seedForTreehashIndex *= 2;
count++;
}
OTSseed = _gmssRand.NextSeed(Seed);
ots = new WinternitzOTSignature(OTSseed, GetDigest(_msgDigestType), _otsIndex[H]);
treeToConstruct.Update(ots.GetPublicKey());
}
if (treeToConstruct.IsFinished())
return treeToConstruct;
return null;
}