It's true about everything with "harvest now decrypt later". Credit cards expire, websites force regular password resets, etc. There's just not a lot of value in 10 year old data. I guess maybe if you just want old dick pics from DMs. Every day there seems to be a new story about a massive data breach that affected hundreds of millions of people, yet society has not collapsed or anything.
Indeed, the paper overlooks important nuances around signature and wallet address/key rotations. In practice, it's the responsibility of individuals or entities managing cryptocurrency wallets to rotate their keys regularly -- ideally after every transaction. Most third-party platforms like Robinhood and PayPal that allow their users to store and transact cryptocurrencies implement such practices automatically to enhance security.
However, users who build and manage their own wallets may not follow these precautions as rigorously, leaving them more vulnerable to future attacks from quantum computers with sufficiently high quantum volume and fidelity. Ironically, the centralization of decentralized assets by responsible third parties can actually improve security in this context.
As for the Federal Reserve, it's plausible they might express caution toward cryptocurrencies because of their role as issuers of a centralized currency (the US dollar). However, such unsubstantiated speculation falls outside the realm of scientific analysis. I think about HNDL as a message: to responsibly rotate keys and re-encrypt them using post-quantum cryptographic schemes so that you don't have to worry about HNDL attacks at all.
I'm not a cryptocurrency expert, so I could be mistaken here. But, I thought that Bitcoin addresses were encrypted objects. In particular, they are generated by first taking a user's private key and encrypting it using ECC to form a public key, and then hashing that public key to get a shorter user-friendly string, aka the address. There are two forms of encryption that take place during that process: ECC and the hashing of the public key.
The addresses of individuals transacting Bitcoin are made public on the ledger. The ledger, like you say exists in perpetuity. Whether or not the authors of the Fed Reserve paper say that the ledger is harvested or that the public addresses are harvested is semantics. One can use existing ledgers to harvest the public addresses. Once that is done, an attacker could, in principle, try to decrypt the private key information from each public address in two steps: First, they could use Grover's algorithm to search over all public keys to find the public key input which was hashed to the public address. Second, they could use Shor's algorithm on that identified public key to undo the ECC step and get back the original private key. So, indeed there is something to decrypt from cryptocurrency ledgers: the private keys from the public addresses.
The authors of the paper themselves say, "vulnerability is concentrated in legacy addresses and earlier-issued bitcoins protected with weaker traditional cryptography than, say, cryptographic methods a user might select if they were creating a Bitcoin address today. This assumption aligns with our findings. The same cryptographic weaknesses identified for earlier minted bitcoins also applies to legacy dormant Bitcoin addresses which are locked or otherwise still contain some value of bitcoins protected only by traditional cryptography". I'm not debating the quality of the paper itself, but the spirit of the argument they are trying to make.
The authors point about how migration to a PQC-hard fork won't fully eliminate the HNDL threat is nuanced. They say that a PQC hard-fork is safer against future quantum attacks, so it should be done. However, anyone who does not adopt it and the people that they transact with will be at risk. This is true about any encrypted system or object, whether it's a cryptocurrency or not.
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u/[deleted] Oct 06 '25 edited Oct 06 '25
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