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package org.spongycastle.crypto.tls;
/**
* RFC 4347 4.1.2.5 Anti-replay
* <p/>
* Support fast rejection of duplicate records by maintaining a sliding receive window
*/
class DTLSReplayWindow
{
private static final long VALID_SEQ_MASK = 0x0000FFFFFFFFFFFFL;
private static final long WINDOW_SIZE = 64L;
private long latestConfirmedSeq = -1;
private long bitmap = 0;
/**
* Check whether a received record with the given sequence number should be rejected as a duplicate.
*
* @param seq the 48-bit DTLSPlainText.sequence_number field of a received record.
* @return true if the record should be discarded without further processing.
*/
boolean shouldDiscard(long seq)
{
if ((seq & VALID_SEQ_MASK) != seq)
{
return true;
}
if (seq <= latestConfirmedSeq)
{
long diff = latestConfirmedSeq - seq;
if (diff >= WINDOW_SIZE)
{
return true;
}
if ((bitmap & (1L << diff)) != 0)
{
return true;
}
}
return false;
}
/**
* Report that a received record with the given sequence number passed authentication checks.
*
* @param seq the 48-bit DTLSPlainText.sequence_number field of an authenticated record.
*/
void reportAuthenticated(long seq)
{
if ((seq & VALID_SEQ_MASK) != seq)
{
throw new IllegalArgumentException("'seq' out of range");
}
if (seq <= latestConfirmedSeq)
{
long diff = latestConfirmedSeq - seq;
if (diff < WINDOW_SIZE)
{
bitmap |= (1L << diff);
}
}
else
{
long diff = seq - latestConfirmedSeq;
if (diff >= WINDOW_SIZE)
{
bitmap = 1;
}
else
{
bitmap <<= (int)diff; // for earlier JDKs
bitmap |= 1;
}
latestConfirmedSeq = seq;
}
}
/**
* When a new epoch begins, sequence numbers begin again at 0
*/
void reset()
{
latestConfirmedSeq = -1;
bitmap = 0;
}
}
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