Blockstream Publishes Schnorr-Based Test Code for Bitcoin Blockchain Upgrade

The Schnorr-based multi-signature scheme MuSig, a test code for a potential upgrade to the Bitcoin (BTC) blockchain, has been released by blockchain tech firm Blockstream, according to an announcement published on Feb. 18.

Last January, four Bitcoin developers released a paper outlining how Schnorr multi-signatures (‘multisig’) could help scale the Bitcoin blockchain, saying that the technology could reduce its transaction size and “improve both performance and user privacy in Bitcoin”. In the paper, the developers state that MuSig is designed as “a protocol that allows a group of signers to produce a short, joint signature on a common message.”

Today’s announcement reveals that MuSig has been turned from an idea into usable code, while this week the code was also merged into secp256k1-zkp, a fork of secp256k1 representing “the high-assurance cryptographic library used by Bitcoin Core.”

In the post, the developers explain their decision to develop MuSig by creating “a misuse-resistant API without sharp corners, and which doesn’t encourage dangerous usage patterns even in constrained environments.” The post also stresses the necessity of improving verification efficiency and developing provable security in the public key model. MuSig signatures purportedly improve privacy since they hide the exact signer policy.

However, since the beginning of the MuSig development, its creators have reportedly found that a number of already published signature schemes —  including an earlier unpublished version of MuSig — are insecure. The post further reads:

“MuSig signatures, just like Schnorr signatures or ECDSA, use in their construction a secret ‘nonce’ which must be produced uniformly randomly. Any deviation from uniform, even by a single bit, can lead to secret key loss and stolen funds.”

For now, the developers are asking community members to test the code, which is reportedly posted on GitHub, and provide feedback.

Bitcoin’s next halving is expected to happen in May 2020. Bitcoin halving is an event that happens roughly once every four years, after which the amount of new BTC created and earned by miners will be cut in half.

In anticipation of the next halving, United States-regulated trading and clearing platform LedgerX released a new type of derivative contract unique to BTC called LedgerX Halving Contract (LXHC). The new product represents a binary option and reportedly “allows you to get a fixed payoff if the next halving block (#630,000) happens before a certain date and time. If the block is discovered after, the contract expires at zero.”