A cryptographic protocol that enables signers to stay anonymous among multiple public keys in a ring. Borromean ring signatures are used in Liquid in Confidential Transactions to power range proofs, which verify that a transaction's hidden amounts are valid without revealing the amounts, and in the asset surjection proofs that support multiple confidential asset types; they do not hide the identity of the sender, which remains visible through on-chain addresses.
To generate a Borromean ring signature in Liquid, the signer breaks the committed amount into digits and builds a ring for each digit. Each ring's public keys represent the possible values that digit could take, not the public keys of other users. Each ring's size is fixed by the number of possible values its digit can take, not chosen by the signer to scale privacy.
Learn more about Borromean ring signatures by reading the official whitepaper.