DRKey timestamps

[aaronbojarski]

DRKey timestamps for the validity period use unix time in nanoseconds.
This will overflow the uint64_t on Thu Jun 15 2028.

Is nanosecond precision here really needed? If not we could just switch to milliseconds.

[fstreun]

In the new SPAO version, we have addressed this concern (and many others), and changed it.
Im particular, see in particular this PR here:
scionproto/scion#4300

I think, we should move to the new version of the SPAO header.

[aaronbojarski]

Ah okay good to know.
That is anyways on the TODO list.

[fstreun]

I created a new issue (#30) for adapting the new SPAO header format.