Recently our credit card processing page stopped working, and when I contacted the service provider I was told to make sure our system's clock was set correctly. The clock was not quite right, and when I reset it things started working again. Why would the clock setting be a problem, and how can I fix the system so the clock stays accurate?

Accurate timestamps are required by many credit card processing services to ensure that transactions are not being replayed on purpose or by accident. Some cryptographic protocols also may make use of the current time at the start of the transaction-submission process as part of the information used to construct the initial session keys, which are used to establish the encryption and decryption keys for coding and decoding the information involved in the transaction.

Most computer system clocks will drift a little bit and gain or lose time if they are not synchronized to a network time server or reset regularly. Most server operating systems include at least basic support for enabling Network Time Protocol (NTP) client services to automatically keep the server synchronized to network time. In Windows systems turn on the Windows Time Service under Services in Control Panel. For Unix-based systems make sure the ntpd or xntpd service daemon is running. NTP will keep your system time set to network time.