A method and system that protects against a replay attack in a closed system postage meter is provided. "Freshness" data is included along with each indicium message sent from the meter to the printer, thereby enabling the printer to detect "stale" indicium data, i.e., indicium data that was previously generated and is being replayed, and prohibit the printing of duplicate indicia. The freshness data includes a random nonce generated by the printer during initialization along with sequence data that the printer can verify against sequence data from the previous printed indicium. If in the current indicium message the nonce is different or the current sequence data is not greater than or equal to the sequence data from the previous printed indicium, indicating the current indicium data may have been previously generated and is a replay, the printer will not print the current indicium data.