Patent ID: 7349537

Claim:
A method for decrypting downstream data in an Ethernet passive optical network (EPON), comprising: receiving a data frame which is encrypted based on a remote input block and a session key, wherein the remote input block is constructed based on a remote cipher counter and a remote block counter; adjusting a local cipher counter based on a received checksum located in a preamble of the data frame, wherein the local cipher counter is synchronized with the remote cipher counter; truncating the local cipher counter by discarding n least significant bits thereof, wherein n is equal to 5, wherein the untruncated local cipher counter is more than 5 bits long, and wherein a portion of the untruncated local cipher counter is identical to a local multi-point control protocol (MPCP) counter; constructing a local input block based on the truncated cipher counter and a local block counter for the received data frame; and decrypting the data frame based on the local input block and the session key.