This bulletin describes a modification to Monero's linkable ring signature scheme that permits dual-key outputs as ring members. Key images are tied to both output one-time public keys in a dual, preventing both keys in that transaction from being spent separately. This method has applications to non-interactive refund transactions. We discuss the security implications of the scheme.
We present threshold ring multi-signatures (thring signatures) for collaborative computation of ring signatures, present a game of existential forgery for thring signatures, and discuss uses of thring signatures in digital currencies that include spender-ambiguous cross-chain atomic swaps for confidential amounts without a trusted setup. We present an implementation of thring signatures that we call linkable spontaneous threshold anonymous group signatures, and prove the implementation existentially unforgeable.
Monero uses a unique hash function that transforms scalars into elliptic curve points. It is useful for creating key images, in particular. This document, authored by Shen Noether, translates its code implementation (the ge_fromfe_frombytes_vartime() function) into mathematical expressions.
