Subject: Re: [bitcoindev] Re: [Draft BIP] Quantum-Resistant Transition Framework for Bitcoin

From: Alex Pruden <[email-masked]>
Date: Wed, 20 Aug 2025 13:07:38 -0700 (PDT)

I consider the recent work by Mosca et al to be the most up-to-date in 
terms of research estimation: 
https://www.sciencedirect.com/science/article/pii/S0167739X24004308

The estimate he provides is approximately an order of magnitude less work 
required to break ECDSA (P-256) vs RSA-2048. Ironically, the longer 
bit-lengths of RSA seem to actually contribute to post-quantum security, 
even though the motivation for moving from RSA-1024 was to protect against 
NFS and other classical attacks against shorter RSA instances. 

Note that the resource estimation in the paper doesn't account for Gidney's 
speedup, which was 20x reduction in qubits required. It's unclear whether 
that same improvement factor could be applied here; as the Gidney paper 
showed, the earliest CRQCs will probably be hardwired for certain circuits 
for performance reasons. E.g. Gidney's circuit layout works for RSA-2048 
and that's it. But the ideas he presents around error correction (e.g. the 
yoked surface code) might apply more broadly, it's hard to say. 

Also note that many of his assumptions are based on a superconducting 
architecture, which generally have faster runtimes but lower stability (so 
scaling is harder)

Other architectures like this one https://arxiv.org/pdf/2506.20660 from the 
neutral atom community have slower runtimes but greater stability. But even 
if you scale, it probably only works for targeted, long-range attacks vs 
specific PKs as a CRQC.

Lots of variables to consider here in terms of estimating the timeline for 
a CRQC, but the proactive approach is probably the right one, because (to 
quote Gidney in his conclusion) we should "*prefer security to not be 
contingent on progress being slow.*"

On Tuesday, August 12, 2025 at 3:04:32 AM UTC-6 ArmchairCryptologist wrote:

>
> An astute observation. To clarify the quantum computing landscape: 
> Google's current quantum processors do not possess 50 logical qubits, and 
> even if they did, this would be insufficient to compromise ECDSA - let 
> alone RSA-2048, which would require approximately 20 million noisy physical 
> qubits for successful cryptanalysis [0].
>
>
> That paper is pretty old. There is a recent paper from a couple of months 
> ago by the same author (Craig Gidney from Google Quantum AI) claiming 
> that you could break RSA-2048 with around a million noisy qubits in about a 
> week. 
>
> Paper: https://arxiv.org/pdf/2505.15917
> Blog post: 
> https://security.googleblog.com/2025/05/tracking-cost-of-quantum-factori.html
>
> I can't say for sure whether this approach can be applied to ECDSA; I have 
> seen claims before that it has less quantum resistance than RSA-2048, but 
> I'm unsure if this is still considered to be the case. And while these 
> papers are of course largely theoretical in nature since nothing close to 
> the required amount of qubits exists at this point, I haven't seen anyone 
> refute these claim at this point. These is still no hard evidence I'm aware 
> of that a quantum computer capable of breaking ECDSA is inevitable, but 
> given the rate of development, there could be some cause of concern.
>
> Getting post-quantum addresses designed, implemented and activated by 2030 
> in accordance with the recommendations in this paper seems prudent to me, 
> if this is at all possible. Deactivating inactive pre-quantum UTXOs with 
> exposed public keys by 2035 should certainly be considered. But I still 
> don't feel like deactivating pre-quantum UTXOs without exposed public keys 
> in general is warranted, at least until a quantum computer capable of 
> breaking public keys in the short time between they are broadcast and 
> included in a block is known to exist - and even then, only if some 
> scheme could be devised that still allows spending them using some 
> additional cryptographic proof of ownership, ZKP or otherwise.
>
> --
> Best,
> ArmchairCryptologist
>

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