A Quantum-Safe Blockchain?

I noted earlier that the arrival of quantum computing (QC) is a dire threat to the Internet in general and cryptocurrency in particular. Despite the rhetoric about how groundbreaking the Nakamotoan blockchain [2] was, the implementation of Bitcoin is hardly technically cutting edge. Based on easily available cryptography currently used on the Internet, there was no consideration of the expected arrival of QC. It has arrived [3], and Bitcoin is obsolete.

What is to be done? That is not clear. There are no known ways to make the current Bitcoin protocol and data structures “quantum safe” let alone secure the rest of the Internet that Bitcoin relies on.

Last week there was excitement about an announcement from the Russian Quantum Center, which reports that they have developed “the first quantum safe blockchain” [1]. I’m far from expert on Quantum Key Distribution (QKD), but the basic idea is to replace public key based digital signatures with QKD. This addresses the greatest vulnerability in the blockchain. (I’m not positive that this addresses all the vulnerabilities, but I really don’t understand this technology very well.)

This is a good idea, indeed, an obvious approach. Problem solved!

Actually, it’s not clear that this theoretical solution is even relevant to Bitcoin in the real world.

First of all, QKC is a method for sharing keys between trusted parties (and it is rare and expensive).   This is great at the root of networks, where there are a relative handful of peers and steps can be taken to establish trust. The current PKI systems, on the other hand, are open source, ubiquitous, and equally available to everyone. We don’t need any “root” to be able to establish trust between us.

It’s not clear how soon we’ll all be able to exchange keys with each other via QKC. Until then, this technology is controlled by the big boys. That’s quite a problem for the decentralized philosophy of Nakamotoan blockchains. If we have to trust the root key managers, then we might as well have centralized servers, no?

Maybe the quantum internet will be deployed quickly, though IPV6 still isn’t fully deployed after 25 years, and there is a whole lot more “net” than there used to be. Depending on what this new architecture looks like, it might or might not be the right stuff for peer-to-peer protocols to run on, anyway.

The system described in the paper is essentially a whole new protocol. I’m not sure how it could be retrofitted on a system which already has zillions of records stored. Even if things were “quantum safe” from now on, would the old transactions be secure and trusted? I dunno.

Regardless of the ultimate usefulness of this or any other “quantum safe” blockchain, it is hard to see how it could ever be adopted by Bitcoin. For the past two years, we have seen Bitcoin thrash, unable to implement a very simple technical upgrade to deal with block sizes.  How in the world will it implement something even more radical, something that may require new hardware and fundamental changes to the system? I’m not holding my breath.

My own guess is that Bitcoin and other similar cryptocurrencies with come down with a sudden crash when quantum equipped hackers break in and steal everything. The end will be swift and irreversible.

It is more likely that this QKD technology will appear in private blockchains, running on private networks. On the other hand, if you have already built a trusted network with QKD, then you may not actually get much benefit from using a blockchain. I dunno. We’ll have to see.

  1. E.O Kiktenko., N.O. Pozhar, M.N. Anufriev, A.S. Trushechkin, R.R. Yunusov, Y.V. Kurochkin, A.I. Lvovsky, and A.K. Fedorov, Quantum-secured blockchain. 2017. https://arxiv.org/abs/1705.09258
  2. Nakamoto, Satoshi, Bitcoin: A Peer-to-Peer Electronic Cash System. 2009. http://bitcoin.org/bitcoin.pdf
  3. National Security Agency, Commercial National Security Algorithm Suite and Quantum Computing FAQ. National Security Agency CNSS Advisory Memorandum MFQ U/OO/815099-15, 2016. https://cryptome.org/2016/01/CNSA-Suite-and-Quantum-Computing-FAQ.pdf


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