Method and apparatus for fast check and update of anti-replay window without bit-shifting in internet protocol security

An apparatus for updating an anti-replay sliding window of (M−1)*N bits without bit shifting, wherein the anti-replay sliding window is defined by a low index and a high index, wherein the apparatus comprises:

• a memory comprising M blocks, where each block contains N bits and M and N are positive integers;
• a receiver configured to receive a packet with a sequence number greater than the high index;
• a processor coupled to the receiver and the memory, wherein the processor is configured to:
• add a difference between the sequence number and the high index to the high index and the low index to generate a new high index and a new low index;
• determine the sequence number is in a first block beyond the block pointed to by the high index;
• based on the determining:
• initialize all bits values in the first block to zero without bit shifting;
• and
• circularly shift the new high index to point to the first block and update the anti-replay sliding window using the new high index and the new low index.