A proof-of-postage generating system (22, 24, 25, 26, 27) wherein funds, application of those funds, the replenishment of those funds and the auditing of those funds are secure against attempts at fraud. The system (22, 24, 25, 26, 27) may either be a Closed System (CS) wherein the proof-of-postage printing means (22) are housed within the system computational means (24, 26) or within a cryptographically secure boundary. Further, the system (22, 24, 25, 26, 27) may be an Open System (OS) wherein the proof-of-postage printing means are external to the system computational means (24, 26).