For several years I have published a leap second table in the DNS. My version(s) of the leap second table are (as far as I know) unique:
They are cryptographically signed: if you get my leap second table you know it came from my workstation.
They have the full history from 1972, in a single DNS query, and this needs less than 100 bytes (plain text) or 20 bytes (binary).
The problem with leap seconds is not how they are published, but the tools that (fail to) disseminate and use the leap second table.
NTP is a big problem: the traditional NTP implementation is designed to choose and fixate on one server out of an ensemble of possible upstreams. Leap seconds are not part of the decision process of choosing which upstream is correct.
As a result, NTP will trust an upstream that is good at keeping time (maybe it is in a room with good temperature stability), but misconfigured for leap seconds, so when a leap second comes along NTP gets surprised by a sudden one-second offset.
There at least two plausible ways to avoid being surprised:
Make your NTP server get the leap second table from a trusted source, e.g. my DNS records. If your upstream NTP server’s leap indicator bits disagree with the correct table, expect that it will go wrong when a leap second happens.
Get NTP servers to disseminate the table, and only trust upstreams that agree with the majority. The table is less than 20 bytes (600x smaller than the NIST table) so it can easily fit in an NTP packet.
Make it cheap to distribute the leap second table.
Done, but my spec needs more rigor. My binary leap second table is smaller than a SHA-1 hash, so it is cheaper to distribute the whole thing than a digest.
Make NTP distrust upstreams that disagree with the leap second table when a leap second is pending.
This is the hard part, because it involves persuading multiple open source and proprietary implementers.
But I will happily rant about precise time keeping at the Cambridge Beer Festival to anyone who talks about their project to refurbish a rubidium frequency standard [not a hypothetical example] and I will try not to bore people who are not time nuts….
I thought that this week I might work on polishing my spec for compact leap second tables, or writing an implementation in Rust, but I have decided that tackling the oppressive todo list of procrastinatory doom will make me happier.