Signer revocability for threshold ring signatures

Abstract

$t$-out-of-$n$ threshold ring signature (TRS) is a type of anonymous signature designed for $t$ signers to jointly sign a message while hiding their identities among $n$ parties that include themselves. However, can TRS address those needs if one of the signers wants to revoke his signature? Can non-signers be clipped without compromising anonymity? Current research has only addressed the functionally opposite property, namely, extendability. In this paper, we introduce the revocability of TRS, addressing the need for improved flexibility and privacy security. Specifically, we innovatively define two properties: revocability, allowing signers to revoke their identities non-interactively and update the signature from $t$-out-of-$n$ to $t-1$-out-of-$n$; and clippability, enabling removal of non-signers from the ring. The synergy of these two properties enables dynamic revocation while keeping the signature size minimal. We analyze and define the boundaries of these operations, provide the DL-based constructions, and prove the security of the schemes. The asymptotic complexity of our approach reaches the same level as that of existing solutions, and especially when using larger ring sizes, experimental results demonstrate that it can effectively reduce the signature size.