nChain Authors Rabin Signatures in Bitcoin Cash For Signing and Verifying Messages for BCH

Signing and Verifying Messages in BCH Script Via Rabin Signatures

One of the newly proposed changes to the Bitcoin Cash script is the introduction of a possibility of signing and verifying arbitrary messages without introducing additional opcodes. So far, to validate Bitcoin Cash (BCH) transactions, opcodes like OP_CHECKDATASIG or OP_DATASIGVERIFY were a necessity.

The problem is that they are not part of Bitcoin's original protocol. But what if there was no need for them anymore? What if arbitrary messages could be signed directly in Bitcoin BCH script? Well, a new solution proposes just that.

The Use of Rabin Signatures

According to the new article by Owen Vaughan, a senior researcher at nChain, the solution lies in an algorithm called RDS (Rabin Digital Structure). RDS' algebraic structure can allow pretty much any piece of transaction data to be signed, even if it originated outside of the Bitcoin BCH chain.

RDS was developed by Michael Rabin back in 1971 and is considered to be among the first schemes regarding digital signatures. In his article, Vaughan explains that the algorithm's security is relying on the fact that modular square-root calculations are as hard as integer factorization. According to him, it is pretty similar to RSA, in a way that they both share numerous features, but there are also a lot of important differences.

Vaughan even provides an example of how arbitrary messages can be signed, and how the signatures can be directly verified in BCH script, with no additional opcodes being necessary to complete the process. All other operations, such as the construction of the signature, or key generation, can be done off-block, and the only part that needs to be done within scripts is the verifying itself.

Additionally, the algorithm remains existentially unforgeable, which would allow for numerous extra functionalities. These functionalities can easily become available at BCH platform, while the original protocol remains unchanged. It is also important to note that adding them would not compromise the network's security either.

According to nChain itself, there are already plans for developing a solution that would be based on Rabin signatures. Additionally, the company is willing to work on developing such a solution alongside other researchers and groups that might be interested in a collaboration. Also, according to Vaughan, there are no plans by the outfit to patent this work. Instead, it will be published publicly, for everyone to see and use.