| 摘要 |
A cryptographic method for providing a level of security by a postage security device (60), which generates a digital token (62) using a cryptographic key (64). When it is required to make a key change in order to improve the level of security, the postage security device (60) replaces the cryptographic key (64) with a new cryptographic key, wherein the new cryptographic key has a key length that is equal to or greater than the replaced cryptographic key. The new cryptographic key can be generated by the postage security device (60) based on a given key length, or selected from a plurality of replacement keys stored in a storage device (54). |
