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If a device has been disconnected from power long enough to drain its clock battery, or has no clock battery at all, and its potential lifespan is longer than the duration of a certificate, what assurance can its NTP client have (assuming it can't rely on a trusted human to provide the approximate date) that its network connection is not controlled by an impostor who has had enough time to brute-force the server's private key, use it to backdate the time to when its certificate was still valid, and simulate an older time by e.g. truncating blockchains and Git branches to older versions? NeonMerlin 23:38, 12 December 2021 (UTC)
enough time to brute-force the server's private key, you're talking about a seriously science-fictional scenario. Using brute force to find a typical 256-bit key would require checking, on average, possible keys. If you had a network of a trillion computers, each of which could check a trillion keys per second, it would still take you over years to test that many keys. CodeTalker (talk) 01:10, 14 December 2021 (UTC)