Multisig and segwit

The document discusses multisignature (multisig) addresses and Schnorr signatures. It explains that multisig addresses require signatures from multiple private keys to authorize transactions. Schnorr signatures could improve upon the currently used ECDSA signatures by having shorter signatures and providing signature aggregation for multisig transactions. The document also covers how Practical Byzantine Fault Tolerance (PBFT) consensus protocol works and how Schnorr-based multisignatures could lower communication costs for PBFT from quadratic to linear scaling.