“Another area of focus for Blockstream is digital signatures. The company has developed Cross Input Signature Aggregation (CISA/XISA), which enables multiple inputs in a single transaction to share a single signature, reducing the size of transactions and improving the efficiency of the Bitcoin network.”

https://bitcoinmagazine.com/business/blockstream-formalizes-research-team?utm_source=carrot&utm_medium=partner&utm_campaign=carrot_share