Blockchain-based e-voting promises immutable, end-to-end verifiability, yet its very transparency threatens voter anonymity. Existing counter-measures fall short: zero-knowledge proofs and blind signatures impose prohibitive computation and still leak ballot semantics, while linkable ring signatures, where each voter cloaks her identity behind a crowd of mixins, succumb to set-level de-anonymization attacks that correlate multiple ballots. We introduce dynamic ring signature, the first mechanism to deliver provable anonymity for an entire election, not merely individual ballots. Instead of sampling mixins at random, dynamic ring signatures select them strategically via a maximum-flow formulation whose correctness we formally prove; the resulting rings simultaneously frustrate linkage and remain publicly verifiable. To scale the technique, we give a lightweight heuristic that greedily maximizes ideological diversity among mixins, slashing both ring size and computation time. Analysis and experiments show that dynamic ring signature achieves stronger anonymity than prior work with an order-of-magnitude reduction in mixins and runtime.