Designing Workflow Components for e-Science

A postage meter includes printing and accounting stations interconnected through an insecure communications link. Each time the meter is tripped, a number generator at the printing station is activated to generate a number signal which is encrypted to provide an unpredictable result. The number signal is also transmitted to the accounting station. At the accounting station the postage to be printed is accounted for and the number signal is encrypted to provide a reply signal. The reply signal is transmitted to the printing station where a comparator compares it with the encryption result generated at the printing station. An equality of the encryption result and the reply signal indicates that the postage to be printed has been accounted for and the printer is activated.