DER encoding

Developers are highlighting a quirk of X.509 digital certificates: the validity period is the only field represented as human-readable text, while everything else is strictly DER-encoded binary. The point being made is that a strict DER parser effectively needs calendar logic, not just clock logic, to handle dates correctly. The observation has drawn attention among programmers working in Python, fintech and cryptography, who see it as a neat example of how messy real-world standards can be.