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Jeroen W. Pluimers on .NET, C#, Delphi, databases, and personal interests

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ssl – Why was 398 days chosen for TLS expiration? – Stack Overflow

Posted by jpluimers on 2026/01/01

Cool, since I switched to Let’s Encrypt a long while ago, I missed that various tools now require TLS expiration be no longer than 398 days away (and preferably even 397 days).

So I also missed the reason for that specific number of days. [Wayback/Archive] ssl – Why was 398 days chosen for TLS expiration? – Stack Overflow (thanks [Wayback/Archive] stevendesu and [Wayback/Archive] user10063)

answers it:

366+31+1 = 398 days

It equals one leap year + one month + “a little room to handle the messiness of dates.”

then posts a lot of quotes from references to the history on how that reason came to be. I have archived and listed the links below.

Most of the discussion was during a very hectic time in life: after a single sided bad accident my mentally retarded brother was in and assisting him during his recovery period, I developed cancer and had extensive treatments against it. All the more reason for missing all this:

–jeroen

This entry was posted on 2026/01/01 at 12:00 and is filed under Communications Development, Development, Encryption, https, HTTPS/TLS security, Internet protocol suite, Let's Encrypt (letsencrypt/certbot), Power User, Security, TCP, TLS. Tagged: , . You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.

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