On 4/25/19 6:10 PM, Björn Persson wrote:
It's perfectly possible for a number to be unique without being random. As an example, you could hash the machine ID, which is supposedly unique in space, and the system clock, which is unique in time. That makes the hash unique in both space and time. Produce invocation IDs by counting up from that value, or by hashing repeatedly. That way you wouldn't need entropy for invocation IDs at every boot, only during installation. Such values would of course be somewhat predictable, but according to what you've said in this thread, invocation IDs don't need to be unpredictable. You've only said that you want them unique.
That is a good point---and by the way, you COULD make the same argument for hashing: one could create another installation-time seed value that will be guaranteed to not leak from the system, and mix it in the hash creation, making the hash unpredictable.
Between those two workarounds, it looks to me like we don't need randomness in secular systemd startup at all?
(Of course one needs to be aware that collisions are not impossible, only improbable. That's equally true for hashes and random numbers.)
At the UUID-level bit lengths, the probability is vanishingly small---although one does have to realize that even very small probability events can be realized with enough statistics, like in this recent measurement of Xenon124 radioactive decay with time constant of over 10^22 years, trillion times longer than the life of the Universe:
https://www.nature.com/articles/s41586-019-1124-4 _______________________________________________ devel mailing list -- devel@xxxxxxxxxxxxxxxxxxxxxxx To unsubscribe send an email to devel-leave@xxxxxxxxxxxxxxxxxxxxxxx Fedora Code of Conduct: https://getfedora.org/code-of-conduct.html List Guidelines: https://fedoraproject.org/wiki/Mailing_list_guidelines List Archives: https://lists.fedoraproject.org/archives/list/devel@xxxxxxxxxxxxxxxxxxxxxxx
