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using System;
namespace Org.BouncyCastle.Tls
{
/**
* RFC 4347 4.1.2.5 Anti-replay
* <p>
* Support fast rejection of duplicate records by maintaining a sliding receive window
* </p>
*/
internal sealed class DtlsReplayWindow
{
private const long ValidSeqMask = 0x0000FFFFFFFFFFFFL;
private const long WindowSize = 64L;
private long m_latestConfirmedSeq = -1;
private ulong m_bitmap = 0;
/// <summary>Check whether a received record with the given sequence number should be rejected as a duplicate.
/// </summary>
/// <param name="seq">the 48-bit DTLSPlainText.sequence_number field of a received record.</param>
/// <returns>true if the record should be discarded without further processing.</returns>
internal bool ShouldDiscard(long seq)
{
if ((seq & ValidSeqMask) != seq)
return true;
if (seq <= m_latestConfirmedSeq)
{
long diff = m_latestConfirmedSeq - seq;
if (diff >= WindowSize)
return true;
if ((m_bitmap & (1UL << (int)diff)) != 0)
return true;
}
return false;
}
/// <summary>Report that a received record with the given sequence number passed authentication checks.
/// </summary>
/// <param name="seq">the 48-bit DTLSPlainText.sequence_number field of an authenticated record.</param>
/// <param name="isLatestConfirmed">indicates whether <paramref name="seq"/> is now the latest confirmed
/// sequence number.</param>
internal void ReportAuthenticated(long seq, out bool isLatestConfirmed)
{
if ((seq & ValidSeqMask) != seq)
throw new ArgumentException("out of range", "seq");
if (seq <= m_latestConfirmedSeq)
{
long diff = m_latestConfirmedSeq - seq;
if (diff < WindowSize)
{
m_bitmap |= (1UL << (int)diff);
}
isLatestConfirmed = false;
}
else
{
long diff = seq - m_latestConfirmedSeq;
if (diff >= WindowSize)
{
m_bitmap = 1;
}
else
{
m_bitmap <<= (int)diff; // for earlier JDKs
m_bitmap |= 1UL;
}
m_latestConfirmedSeq = seq;
isLatestConfirmed = true;
}
}
internal void Reset(long seq)
{
if ((seq & ValidSeqMask) != seq)
throw new ArgumentException("out of range", "seq");
// Discard future records unless sequence number > 'seq'
m_latestConfirmedSeq = seq;
m_bitmap = ulong.MaxValue >> (int)System.Math.Max(0, 63 - seq);
}
}
}
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