I've been following an interesting project for a long time now: QRL (the Quantum Resistant Ledger). The QRL is a blockchain that has been up and running for almost two years now. As the name suggests, QRL is a blockchain that is resistant against hacks, even in the future scenario where quantum computers will be able to derive private keys from public keys. (Using quantum algorithms like Shors algorithm.)

Why QRL? Any blockchain needs to communicate and authenticated transactions. These transactions are sent from user devices to the blockchain network. For authentication of transactions, public key cryptography is used. Classical public key cryptography, which is used in any blockchain, will become unsafe when quantum computers of sufficient size are developed. QRL uses the quantum resistant signature scheme XMSS to protect the entire ledger from the very beginning: the QRL genesis block was launched with XMSS as only signature scheme implemented.

Quantum resistant/ post-quantum cryptography

NIST kicked off a post-quantum cryptography project for the standardization of quantum resistant signature schemes. (Read more here about NIST and why it matters for blockchain.) NIST intends to approve XMSS as the first quantum resistant signature scheme. (This is the first approval, aside from the main process that is in development as we speak.) This means that currently, QRL is the only crypto asset using (soon to be) NIST-approved post-quantum cryptography. An interesting detail is that Bruinderink, who is mentioned in the NIST announcement about the XMSS approval, is the main adviser of the QRL project. We can rest assure that QRL's implementation of XMSS is done professionally and correct. (They also had 2 external audits.)

The challenge for existing blockchains to switch to quantum resistant cryptography

Everything digital will eventually need to switch from classical cryptography to quantum resistant cryptography. This will be a challenge. There will be no plug and play replacement for current signature schemes. Several options will be available and several different methods of implementation would be possible. For centralized systems like banks, nuke codes, e-mail services etc. this transition will be a challenge, but manageable. Decentralized systems like blockchain will face a more challenging and most of all, time-consuming process. Blockchain will face specific additional challenges:

Need for consensus (Not guaranteed since there are several options to reach quantum resistance)

The human factor (after the blockchain upgraded, all coins must be migrated to new quantum resistant addresses by users personally)

A solution must be found for lost addresses (users who lost keys can't access the coins anymore, which means that those coins can never be protected and will stay vulnerable to quantum hacks for ever)

Combined, the biggest risk will be the time factor. (What time-frame is needed for going full quantum resistant for existing blockchains. I wrote a full article about the subject: Going Quantum Resistant In Blockchain: A Plausible Time-frame?)

Starting out early by building a new blockchain from scratch and start out fully quantum resistant will obviously avoid these difficulties.

Upcoming hardfork and new features:

QRL has been steadily and quietly developing over the past two years. Among other things, it added the option to create Quantum secure tokens, notarization, mobile wallet and full ledger hardware wallet support. It has a small but strong community. On April the 6th, the QRL will hardfork and add two interesting new features:

Quantum secure multisignature addresses & transactions: Multisig allows multiple parties governance over how allocated funds can be spent.

Ephemeral messaging latticeTX — Project Mercury

We all heard of multisig wallets. But Ephemeral Messaging? It will allow you to create a communication system that is:

Blockchain-based and decentralized: we all know what that means. But now instead of the bank, you take out the phone company.

Ephemeral: like snapchat, the message isn't stored anywhere, so it's a burn after reading.

But it's also like whatsapp where only the sender and the receiver get to be able to read the encrypted message.

Post-quantum cryptography: meaning not even a quantum computer can hack this data. It's quantum secure.



You can read the whitepaper on QRL's Ephemeral Messaging System here.

Quantum resistant blockchain: general info.

If you are interested in blockchain and quantum resistance: I wrote a seven part series about this that covers pretty much everything on the subject. Total reading time is about one hour, but it will safe you a lot more time in research. Sources included.

It covers:

Blockchain basics: what is a hashing also, what is a signature scheme, how are they used in blockchain and why are they important.

Why hashing algo's aren't the issue, and why the signature scheme is the vulnerable part.

What are the challenges and impossibilities for existing blockchains when they want to upgrade to a quantum resistant signature scheme, and why it is different for the rest of the internet because of the fact blockchain is decentralized and other systems are centralized. (No plug and play replacement for current signature schemes, NIST quoted. Specific challenges for blockchain due to it's decentralized nature: Need for consensus, human factor (after the blockchain upgraded, all coins must be migrated to new quantum resistant addresses by users personally), lost addresses (users who lost keys can't access the coins anymore, which means that those coins can never be protected and will stay vulnerable to quantum hacks for ever) and the time factor.

BTC misconception: it is often said that not reusing addresses would make BTC quantum resistant, which is not true, fully explained in part six. Lately Pieter Wuille, BTC dev, acknowledged that on twitter, here and here.

Loose ends, where is explained why any attempt to become quantum resistant without the use of a quantum resistant signature scheme is useless.

The big question remains when any form of urgency will be necessary. Predictions very immensely, but progress is being made. A few months ago, quantum supremacy was achieved by Google. No need for panic, but keeping an eye on the subject won't hurt. And QRL is an interesting project, with a very helpful community. They are most active on Discord. But you can also follow developments on Reddit.

So far the subject is downplayed a lot and there is a lot of misinformation spread in the cryptospace. To set the record straight, I wrote two articles specifically adding information and insights, specifically as a response to two major sources: