Researchers from Blockstream, a major developer of Bitcoin-based solutions, have published a draft of a new digital signature scheme called SHRINCS. It aims to make Bitcoin transactions resistant to hacking by quantum computers while maintaining the network's throughput.
This is the second technical solution proposed to protect Bitcoin from the quantum threat in recent days. Earlier, StarkWare developed its own method to protect a Bitcoin transaction from a potential attack using a special signature.
A quantum attack on a blockchain essentially boils down to recovering a private key from a public key. In existing systems, this is considered a computationally infeasible task; however, quantum algorithms potentially allow it to be solved significantly more efficiently.
In practice, this implies two scenarios. In the first, an attacker finds addresses where the public key has already been exposed and gains access to the funds by calculating the private key. In the second scenario, they intercept a transaction before it is included in a block, extract the public key, calculate the private key, and replace the transaction. In the second case, not only old or inactive wallets are at risk but also ordinary transfers. Blockstream's development addresses this second scenario.
The new defense method from Blockstream involves a special signature called SHRINCS, which is based on the SHA-256 hash function—the very same one already used in Bitcoin mining. The developers chose an option to protect Bitcoin using already proven and familiar mechanisms.
One of the key goals of SHRINCS was preserving the network's throughput. Blockstream estimated that Bitcoin could process about three transactions per second using this variant, compared to the current network capacity of about seven transactions. They noted that some alternative options reduce this figure to 0.36 transactions per second.
The security proof for Blockstream's variant is currently in a "pending" status, and the corresponding software has not been audited and is not intended for production use. However, in March, the company conducted tests with such transactions on the Liquid sidechain—one of the largest Layer 2 networks based on Bitcoin, also developed by Blockstream.
Over the past year, Bitcoin developers have been discussing various paths for migrating to post-quantum cryptography. Work is underway not only in Bitcoin but across the entire crypto market, and the seriousness of the threat is confirmed by the tens of millions of dollars directed towards developing protection measures for the leading cryptocurrency.
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