Production ZK: Privacy Pools, Identity, Rollups
Where ZK is actually shipping in 2025-2026: privacy pools after Tornado Cash, identity (World ID, Privado), zkBridges (Polyhedra, Succinct), and production zkEVMs.
30 min · expert · part of ZK Cryptography & Proof Systems
From Theory to Production
By 2025-2026, zero-knowledge proofs have moved from theoretical breakthrough to deployed infrastructure. Billions of dollars of transaction value settle via ZK proofs every month across rollups. Millions of users hold ZK-backed identity credentials. Privacy pools have evolved from a single application (Tornado Cash) into a category with multiple competing designs. And zkBridges are quietly displacing the trusted-multisig bridges that dominated 2020-2022.
This lesson surveys where ZK is actually shipping. It is not exhaustive — the space is too large and evolves too quickly — but it covers the categories you are most likely to encounter, with concrete projects and the events that shaped them. Three categories are particularly load-bearing: privacy applications (after Tornado Cash), identity systems (World ID and adjacent), and scalability (zkEVMs and ZK rollups).
A consistent theme: ZK is not just about privacy. The single largest production use of ZK proofs today is scalability — rollups using validity proofs to compress execution onto Ethereum without compromising trust. Privacy is the harder political problem; scalability is the bigger economic one.
Also in this lesson
- Tornado Cash and the Privacy Pool Reset
- ZK Identity: World ID, Privado, and Selective Disclosure
- Production zkEVMs and ZK Rollups
- zkBridges: ZK for Trustless Cross-Chain
- Where ZK Is Going
Key terms
- Tornado Cash
- A 2019 Ethereum mixer using Circom Groth16 proofs. Sanctioned by OFAC on August 8, 2022; the Fifth Circuit ruled in Van Loon v. Treasury (Nov 26, 2024) that immutable smart contracts are not property OFAC can sanction under IEEPA; OFAC delisted the contracts in March 2025.
- Privacy Pools
- A design proposed in a September 2023 paper co-authored by Vitalik Buterin and others in which users prove their funds are part of a "permitted" subset of deposits, enabling privacy while cryptographically dissociating from known illicit activity; an actual Privacy Pools protocol launched on Ethereum in 2024-2025.
- Aleo
- A privacy-focused L1 blockchain using zk-SNARKs and the Leo smart contract language. Mainnet launched September 25, 2024.
- Aztec Network
- A privacy-focused L2 using Noir for smart contracts and a private-by-default state model; progressed through testnets toward mainnet through 2024-2025.
- World ID
- A proof-of-personhood protocol using iris-scanning hardware (the Orb) and Semaphore-based ZK proofs of group membership; lets users prove they are unique humans without revealing which human.
- Semaphore
- A Circom-based ZK anonymity primitive developed by the Privacy and Scaling Explorations group; lets users prove group membership and anonymously signal while preventing double-signaling. Underlies World ID and many other systems.
- Privado ID
- A decentralized identity system (rebranded from Polygon ID in 2024) based on the iden3 protocol; users hold verifiable credentials and produce ZK proofs of selective attribute disclosure.
- zkBridge
- A cross-chain bridge architecture using ZK proofs of source-chain consensus signatures and block headers, allowing destination chains to verify cryptographically rather than trust an external validator multisig.
- Polyhedra Network
- A commercial provider of ZK light-client bridges between EVM and non-EVM chains; one of the leading production zkBridge implementations.
- Succinct Telepathy
- A ZK light client for Ethereum, providing other chains with cryptographic verification of Ethereum block headers; integrated into the broader Succinct SP1 ecosystem.
Continue this lesson — 5 more sections in the CryptoBipto app.
Open lessonEducational only — not financial advice.