An anonymous reader quotes a report from Ars Technica: A few months ago, an engineer in a data center in Norway encountered some perplexing errors that caused a Windows server to suddenly reset its system clock to 55 days in the future. The engineer relied on the server to maintain a routing table that tracked cell phone numbers in real time as they were being moved from one carrier to the other. A jump of eight weeks had dire consequences because it caused numbers that had yet to be transferred to be listed as having already been moved and numbers that had already been transferred to be reported as pending. “With these updated routing tables, a lot of people were unable to make calls, as we didn’t have a correct state!” the engineer, who asked to be identified only by his first name, Simen, wrote in an email. “We would route incoming and outgoing calls to the wrong operators! This meant, e.g., children could not reach their parents and vice versa.”
Simen had experienced a similar error last August when a machine running Windows Server 2019 reset its clock to January 2023 and then changed it back a short time later. Troubleshooting the cause of that mysterious reset was hampered because the engineers didn’t discover it until after event logs had been purged. The newer jump of 55 days, on a machine running Windows Server 2016, prompted him to once again search for a cause, and this time, he found it. The culprit was a little-known feature in Windows known as Secure Time Seeding. Microsoft introduced the time-keeping feature in 2016 as a way to ensure that system clocks were accurate. Windows systems with clocks set to the wrong time can cause disastrous errors when they can’t properly parse time stamps in digital certificates or they execute jobs too early, too late, or out of the prescribed order. Secure Time Seeding, Microsoft said, was a hedge against failures in the battery-powered on-board devices designed to keep accurate time even when the machine is powered down.
“You may ask — why doesn’t the device ask the nearest time server for the current time over the network?” Microsoft engineers wrote. “Since the device is not in a state to communicate securely over the network, it cannot obtain time securely over the network as well, unless you choose to ignore network security or at least punch some holes into it by making exceptions.” To avoid making security exceptions, Secure Time Seeding sets the time based on data inside an SSL handshake the machine makes with remote servers. These handshakes occur whenever two devices connect using the Secure Sockets Layer protocol, the mechanism that provides encrypted HTTPS sessions (it is also known as Transport Layer Security). Because Secure Time Seeding (abbreviated as STS for the rest of this article) used SSL certificates Windows already stored locally, it could ensure that the machine was securely connected to the remote server. The mechanism, Microsoft engineers wrote, “helped us to break the cyclical dependency between client system time and security keys, including SSL certificates.”
