This is falling for an xkcd 538 fallacy, btw. Nation states obviously have vast higher capability to subvert individual data than brute forcing its crypto. I stand by what I said: 1024-bit RSA keys are "fine" and will remain so. RSA-309 will not fall within our lifetime.
> it's very much possible that factoring is much easier than expected
And this is sort of toothless? I mean, that's true for ECC too. It's true for all cryptography. It's true for all software. For all engineering. For all math. We'll never know what we don't know. New discoveries tomorrow may upend everything any given property ("safety" is just one) we think our existing machines hold.
But they probably won't. And the moments where that happens are extremely rare. And to be blunt RSA already got hit with that particular lightning bolt.
"SHA2 will never be broken in our lifetimes" is something I've heard JP Aumasson say many times, but that's based on the fact that there's no line of sight anywhere to techniques that could break it. But you can't say that about 1024 bit RSA.
If you want to pin me down on something slightly more formal: DRAM density scaling kinda stopped a few years back, systems aren't getting any bigger (much to Sam Altman's public dismay), and there is a superlinear matrix size requirement in factorization techniques that AFAIK no one knows how to fix. We can get the cycles to do it, but not the space.
Probably. Maybe not! But even so, it will remain cheaper to steal my secrets with the proverbial $5 wrench. RSA? It was fine.
Another way cryptography breaks is via iterative improvements. For example, in the last few months there are two big cryptanalytic stories
1. The novel scheme (though not standardized) HAWK had its security reduced by ~1/2 by AI. It is no longer compelling in any way. This was in a sense "predictable" though. There was a series of papers showing that HAWK-like schemes were vulnerable to an attack of this type. Then, AI was able to bridge the gap and apply these attacks directly to HAWK.
2. The ISO-standardized scheme McCliece (from ~45 years ago) has had some alarming security reductions, and may be effectively broken (it's still a little early to tell, many cryptanalytic papers require heuristics that must be justified, etc). Again, this was in a sense "predictable". Starting ~3 years ago it was discovered that McCliece had some yet-unexploited structure, and since then there have been more and more papers exploiting this further, until recently more dramatic attacks have occurred.
In both cases, there is a clear "story" you can (post-hoc) tell about the attacks. You can't always predict precisely where the attacks will end up (for the McCliece attack, it appears more effective than I would have predicted at least). But you can often tell when things are gradually weakening, before a full collapse.
RSA has a cousin (binary characteristic finite field DH) that had this gradual weakening into total collapse happen in the 2010s. It is possible this cousin was a problem child, and GNFS will remain the best attack against RSA until quantum computers fully break it. I can't predict the future. But I can say that ECC has had no such problematic cousins.
This is to say that we are blessed that we have extremely strong cryptography available. Why you would choose to use the weakest defensible option is beyond me, and not something anyone serious about security would ever recommend doing. There is no upside, and only downsides.
I still remain confused why people are interpreting this from what I wrote. I'm not "choosing" to use RSA nor advocating for its use. I'm pointing out anecdotally that I have a GnuPG keychain still live with a 1024 bit key from the last millenium (or close to that, honestly I don't know for sure) that everyone was *sure*, 20 years ago, was broken and insecure. And... it wasn't. It's fine.
The xkcd point seems profound to me: the crypto nerds were entirely wrong about their focus and sense of urgency here. Today, it's much cheaper to steal my key with simple violence. It will remain so when I'm on my death bed. Probably when my heirs are too. And I find that interesting. What else are we nerds getting wrong?