ZKP Applications: ZK Rollups & Privacy Coins

Ethereum processes ~15 TPS. Visa: ~1700 TPS. To scale, ZK Rollups batch thousands of transactions off-chain, compute a SNARK proof of their validity, and post the proof on-chain. Validators only verify the proof (1 ms) instead of each transaction.

Users submit transactions to a sequencer. The sequencer batches transactions, executes them off-chain, computes a state transition proof (SNARK/STARK proving the new state root is correct), and posts the proof + compressed calldata to Ethereum L1.

zkSync Era (Matter Labs) is an EVM-compatible ZK Rollup using a custom SNARK (Boojum, based on STARK). Developers deploy Solidity contracts that compile to zkEVM bytecode. Throughput: 2000+ TPS with Ethereum-level security guarantees.

StarkNet uses STARKs (via Stark prover) and the Cairo language. No trusted setup. Programs are compiled to Cairo bytecode, proven with STARKs, and verified on Ethereum. Used by dYdX (v3), Immutable X (NFTs), Sorare (fantasy sports).

Polygon zkEVM uses PLONK-based proofs to emulate the EVM exactly. Any Ethereum smart contract works without modification. The prover produces a PLONK proof for each batch of transactions verifiable on Ethereum L1 in a single transaction.

Zcash (ZEC) uses Groth16 SNARKs (Sapling protocol) to enable shielded transactions: sender, receiver, and amount are all hidden. The SNARK proves the transaction is valid (no double spend, amounts balance) without revealing any private fields.

A Zcash shielded note commits to (value, recipient, randomness) using a Pedersen hash. The SNARK proves: (1) you know the commitment preimage (you own the note), (2) the note is unspent (in the nullifier set), (3) output amounts equal input amounts.

Monero uses ring signatures + Pedersen commitments (RingCT) — no SNARKs, all transactions are shielded by default. Zcash: SNARK-based, transparent and shielded addresses coexist. Monero: simpler crypto, stronger privacy defaults; Zcash: stronger cryptographic guarantees.

ZK identity proofs: prove you are over 18 without revealing birthdate; prove you are a citizen without revealing your passport number; prove you are an accredited investor without revealing net worth. Implementations: Polygon ID, Semaphore (anonymous signaling).

ZK-ML: prove that a neural network inference was computed correctly on private inputs. Used for: medical diagnosis (prove model ran on your data without sharing data), credit scoring (prove model gave a result without revealing inputs). Still research-stage for large models.

ZK proofs enable verifiable outsourced computation: a cloud provider proves it ran a computation correctly, and the client verifies in milliseconds without re-running the computation. Useful for AI inference, data analytics, and trustless bridges.

What does a ZK Rollup post to Ethereum L1 to prove transaction validity?

ZK Rollups (zkSync, StarkNet, Polygon zkEVM) use SNARKs/STARKs for L2 scalability. Zcash uses Groth16 for shielded transactions. ZKPs extend to identity, ML inference, and verifiable outsourced computation. Next: Homomorphic Encryption.