I was a bit surprised that the Android way is not how it works everywhere. I had assumed that the time validation of a TLS certificate chain C0 -> C1 -> C2 ...

I was a bit surprised that the Android way is not how it works everywhere. I had assumed that the time validation of a TLS certificate chain C0 -> C1 -> C2 ... -> Cn went something like this (in pseudocode): 1 time_check = now() 2 for cert in Cn to C0 3 if time_check < cert.valid_from || time_check > cert.valid_to 4 return EXPIRED 5 time_check = cert.issue_time 6 return NOT_EXPIRED but a bit of Googling shows tells me that it works like that pseudocode with line #5 omitted so that all the time checks are against the current time. All certificates in the chain must be valid now. With code signing certificates it does work the way I assumed TLS work. Timestamped code signed with an expired root certificate is still valid as long as the root certificate was valid at the time of the timestamp.