Time stamping is an increasingly valuable complement to digital signing practices, enabling organizations to record when a digital item—such as a message, document, transaction or piece of software—was signed. For some applications, the timing of a digital signature is critical, as in the case of stock trades, lottery ticket issuance and some legal proceedings. Even when time is not intrinsic to the application, time stamping is helpful for record keeping and audit processes because it provides a mechanism to prove whether the digital certificate was valid at the time it was used. Because the growing importance of digital signing solutions has created a corresponding demand for time stamping, many software programs, such as Microsoft Office, support time stamping capabilities. If time stamping is to add real value, though, the time stamp must be secure and tamper-resistant.