Method for verifying the expected postal security device in a postage metering system

A method for verifying that a postal security device (PSD) is the expected PSD and that the PSD has not completed transactions with any other host system, the method comprising the steps of:

• generating a first message in the host system, said first message representing a first PSD status after a last transaction between the host system and any PSD, said first message including data representing at least first transaction dependent data from a first transaction record stored in the host system during the last transaction between the host system and said any PSD, said first transaction dependent data changing for each transaction between the host system and said any PSD;
• encrypting the first message with an encryption key stored in the host system;
• sending the encrypted first message to the PSD;
• decrypting the encrypted first message with a decryption key stored in the PSD;
• generating a second message in the PSD, said second message representing a second status of the PSD after the last transaction between any host system and the PSD, said second message including data representing at least second transaction dependent data from a second transaction record stored in the PSD during the last transaction between said any host system and the PSD, the second transaction dependent data changing for each transaction between the PSD and said any host system;
• and
• comparing the second message to the decrypted first message.