Masanori Ogino omasanori@mstdn.maud.io

RFC 5280 - Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile https://tools.ietf.org/html/rfc5280#section-4.1.2.5

"CAs conforming to this profile MUST always encode certificate validity dates through the year 2049 as UTCTime; certificate validity dates in 2050 or later MUST be encoded as GeneralizedTime. Conforming applications MUST be able to process validity dates that are encoded in either UTCTime or GeneralizedTime. "