/// <summary>
/// Returns a number
/// </summary>
///
/// <returns>The next pseudo-random index</returns>
public int NextIndex()
{
while (true)
{
if (_remLen < _C)
{
BitString M = _bitBuffer.GetTrailing(_remLen);
int tmpLen = _C - _remLen;
int cThreshold = _callCounter + (tmpLen + _hashLen - 1) / _hashLen;
while (_callCounter < cThreshold)
{
byte[] data = new byte[_Z.Length + 4];
Buffer.BlockCopy(_Z, 0, data, 0, _Z.Length);
Buffer.BlockCopy(IntUtils.IntToBytes(_callCounter), 0, data, _Z.Length, 4);
byte[] H = _digestEngine.ComputeHash(data);
M.AppendBits(H);
_callCounter++;
_remLen += 8 * _hashLen;
}
_bitBuffer = M;
}
// assume c less than 32
int i = _bitBuffer.Pop(_C);
_remLen -= _C;
if (i < (1 << _C) - ((1 << _C) % _N))
{
return(i % _N);
}
}
}
/// <summary>
/// Returns a number
/// </summary>
///
/// <returns>The next pseudo-random index</returns>
public int NextIndex()
{
while (true)
{
if (m_remLen < m_C)
{
BitString M = m_bitBuffer.GetTrailing(m_remLen);
int tmpLen = m_C - m_remLen;
int cThreshold = m_callCounter + (tmpLen + m_hashLen - 1) / m_hashLen;
while (m_callCounter < cThreshold)
{
byte[] data = new byte[m_Z.Length + 4];
Buffer.BlockCopy(m_Z, 0, data, 0, m_Z.Length);
Buffer.BlockCopy(IntUtils.IntToBytes(m_callCounter), 0, data, m_Z.Length, 4);
byte[] H = m_digestEngine.ComputeHash(data);
M.AppendBits(H);
m_callCounter++;
m_remLen += 8 * m_hashLen;
}
m_bitBuffer = M;
}
// assume c less than 32
int i = m_bitBuffer.Pop(m_C);
m_remLen -= m_C;
if (i < (1 << m_C) - ((1 << m_C) % m_N))
{
return(i % m_N);
}
}
}
/// <summary>
/// Constructs a new index generator
/// </summary>
///
/// <param name="Seed">A seed of arbitrary length to initialize the index generator</param>
/// <param name="EncParam">NtruEncrypt parameters</param>
public IndexGenerator(byte[] Seed, NTRUParameters EncParam)
{
_N = EncParam.N;
_C = EncParam.CBits;
int minCallsR = EncParam.MinIGFHashCalls;
_digestEngine = GetDigest(EncParam.Digest);
_hashLen = _digestEngine.DigestSize;
_Z = Seed;
_callCounter = 0;
_bitBuffer = new BitString();
while (_callCounter < minCallsR)
{
byte[] data = new byte[_Z.Length + 4];
Buffer.BlockCopy(_Z, 0, data, 0, _Z.Length);
Buffer.BlockCopy(IntUtils.IntToBytes(_callCounter), 0, data, _Z.Length, 4);
byte[] H = _digestEngine.ComputeHash(data);
_bitBuffer.AppendBits(H);
_callCounter++;
}
_remLen = minCallsR * 8 * _hashLen;
}
/// <summary>
/// Constructs a new index generator
/// </summary>
///
/// <param name="Seed">A seed of arbitrary length to initialize the index generator</param>
/// <param name="EncParam">NtruEncrypt parameters</param>
public IndexGenerator(byte[] Seed, NTRUParameters EncParam)
{
_N = EncParam.N;
_C = EncParam.CBits;
int minCallsR = EncParam.MinIGFHashCalls;
_digestEngine = GetDigest(EncParam.Digest);
_hashLen = _digestEngine.DigestSize;
_Z = Seed;
_callCounter = 0;
_bitBuffer = new BitString();
while (_callCounter < minCallsR)
{
byte[] data = new byte[_Z.Length + 4];
Buffer.BlockCopy(_Z, 0, data, 0, _Z.Length);
Buffer.BlockCopy(IntUtils.IntToBytes(_callCounter), 0, data, _Z.Length, 4);
byte[] H = _digestEngine.ComputeHash(data);
_bitBuffer.AppendBits(H);
_callCounter++;
}
_remLen = minCallsR * 8 * _hashLen;
}