Differentiate between PGP subkey that is expired vs one that never expires - Java bouncycastle

Question

I am using bouncycastle.openpgp library to get the validity dates of a PGP key. A PGP key can be assumed to be never expiring if the key.getValidDays() == 0. How to differentiate between a once valid and now expired key vs a never expiring one?

Answer 1

An expired key, will have a non-zero getValidDays, as they are specified relative to the creation date, not the current one.

getValidDays

public int getValidDays()
Returns:
number of valid days from creation time - zero means no expiry.

I.e. you should be able to differentiate between the never expiring and valid/expired keys, with the code like this:

if(key.getValidSeconds() == 0) {
    //Never Expiring Key
} else if(Instant.now().isAfter(key.getCreationTime().toInstant().plusSeconds(key.getValidSeconds()))) {
    //Expired Key
} else {
    //Valid Key (has not expired yet)
}