Blockstream Unveils Quantum-Resistant Signature Scheme for Bitcoin

Blockstream has developed a post-quantum signature scheme called SHRINCS (Secure Hash-based Reduction of Insecure Signature Schemes) that can protect Bitcoin from quantum attacks without significantly slowing down the blockchain. The company's co-founder and CEO, Adam Back, is skeptical about the threat posed by quantum computers, but he believes it's essential to prepare for it well in advance.

SHRINCS was tested in production on Blockstream's Liquid sidechain in March this year and has been shown to be effective. However, there are some caveats: the scheme is not yet cryptographically mature and requires a security proof that has not yet been completed. Additionally, it introduces additional complexity to Bitcoin.

The size of SHRINCS signatures can grow as large as 4,619 bytes, which is still smaller than most post-quantum signatures but larger than Bitcoin's existing Schnorr signatures. According to estimates, if everyone used Taproot's Schnorr signatures, the blockchain could run at 6.5 transactions per second. However, using SHRINCS would result in a speed of around 3 transactions per second.

Blockstream is also exploring other post-quantum signature schemes and has demonstrated that they can effectively run on common hardware wallets. However, there are some risks associated with these schemes, including the possibility of lost funds if keys are not compatible across different implementations.