Many users are eagerly awaiting the emergence of new technologies that could help Bitcoin cope with the scalability problems it currently faces. These include SegWit, the Lightning Network, and Schnorr signatures. A group of computer scientists proposed a new device to reduce the size of transactions in a multi-signature transfer.
MuSig, to reduce the size of multi-signatures
Bitcoin transactions must necessarily be accompanied by signatures. But these have a flaw: they require, in a block, a lot of space. And the situation is even more problematic when multiple addresses are involved in a transaction – each address will have to register its own signature.
As a result, the size needed to register the transaction increases, which will, in fact, increase the fees associated with these transactions.
By using the Schnorr protocol to limit the number of signatures needed for a transaction, it would be possible to help, in part, Bitcoin to cope with the increase in its popularity. These Schnorr signatures could limit the storage space required, but also the network activity by at least 25%. These new advantages could also help Bitcoin deal with some spam attacks.
Gregory Maxwell, Andrew Poelstra, Yannick Seurin and Pieter Wuille published an article titled Simple Schnorr Multi-Signatures with Applications to Bitcoin. What they propose is a new multi-signature device, based on the Schnorr protocol. Dubbed MuSig, it is defined as “a protocol that allows a group of signatories to produce a common signature, short, in a common message”.
MuSig is a simple multi-signature scheme that is novel in combining:
- support for key aggregation;
- security in the plain public-key model.
MuSig is expected to increase the level of confidentiality as well as the performance of transactions carried out jointly by several individuals. This is what Pieter Wuille wrote:
“A multi-signature scheme is a combination of a signing and verification algorithm, where multiple signers (each with their own private/public key) jointly sign a single message, resulting in a single signature. This single signature can then be verified by anyone who also knows the message and the public keys of the signers.”
In a post, Wouters explained the significance of the technology, saying:
“At the end of the day, if it is just one person sending that transaction from multiple sources, there should be some way to do so with just one signature, right? This is what Schnorr signatures allow us to do.”
Key Aggregation to limit the size of the data
MuSig introduces a new concept: key aggregation. This device reduces to a single number of signatures required for a transaction.
Mr. Wuille gave details in the same article:
“We’re using the term key aggregation to refer to multi-signatures that look like a single-key signature, but with respect to an aggregated public key that is a function of only the participants’ public keys. This means that verifiers don’t actually need to know the original participants’ public keys anymore – they can just be given the aggregated key instead. In some use cases, this leads to better privacy and performance. MuSig is effectively a key aggregation scheme for Schnorr signatures.”
In order to be able to be used again in the context of micro-transactions, Bitcoin will have to face its problems of scalability, which incur costs and consequent transaction delays. The generalization of the SegWit update, but also the arrival of the Lightning Network, could soon allow the first decentralized cryptocurrency to achieve this.