Recently, BCH added the Schnorr signature to the network to improve security and speed up transactions. Blockstream researcher Andrew Poelstra said Bitcoin can achieve better scalability and security with Schnorr signatures. Poelstra said that Bitcoin uses ECDSA because it has an open SSL library. In the early development of Bitcoin, its core cryptography relied entirely on open SSL. In terms of size and performance characteristics, Schnorr signatures provide an alternative to ECDSA, but it makes Bitcoin easy to implement some "unbound protocols" in the network, and implementing Schnorr signatures will help create multiple signatures.