ZK-rollups (zkSync, Starknet): privacy, scalability and taxation

ZK-rollups (Zero-Knowledge Rollups) are Ethereum's most advanced scaling technology. They combine high speed with maximum cryptographic security. Unlike Optimistic Rollups, they do not need a challenge period: the mathematical proof is sufficient.

Why "privacy" with ZK-rollups?

ZK-rollups use Zero-Knowledge Proofs: they prove that a computation is correct without revealing the input data. This allows:

• Validate transactions without the validator knowing the details.
• Potentially: private transactions where the amount and counterparty are hidden.

Important! Most current ZK-rollups (zkSync Era, Starknet, Scroll) do NOT have transaction privacy by default. Transactions are public in the browser. "ZK" privacy is in validity testing, not data confidentiality.

zkSync Era: the L2 from Matter Labs

zkSync Era was launched into production in March 2023. Its features:

• Compatible with EVM (you can use the same tools as in Ethereum).
• Extremely low gas.
• Growing DeFi ecosystem: SyncSwap, Mute.io, zkLend.

ZK airdrop (June 2024):
One of the most anticipated and controversial airdrops. Matter Labs distributed the ZK token:

• Users with zkSync activity history received tokens.
• 17.5% of the total supply distributed in the airdrop.
• Initial price: ~$0.21/ZK.

ZK airdrop taxation:

• Capital gain upon receipt → price of ZK at the time of the claim.
• If you received it in June 2024 at ~€0.21/ZK and you had 1,000 ZK → €210 of capital gain.
• When selling later: second profit/loss according to price evolution.

Starknet (STRK): StarkWare's L2

Starknet uses its own language (Cairo) and has the most advanced ZK architecture. STRK is its native token.

STRK airdrop (February 2024):

• Distributed to early users, contributors and developers.
• Starting price: ~$1.8/STRK.
• Taxation: same as ZK. Capital gain upon receipt.

DeFi on Starknet: Ekubo (DEX), Nostra (lending). Same taxation as in Ethereum.

ZK-proofs and real privacy: Aztec Network

Aztec Network is a ZK-rollup with real transaction privacy:

• Transactions at Aztec are private: amount and participants hidden.
• Similar in terms of privacy to Monero, but based on Ethereum.
• The same tax obligations apply: the user knows his own transactions.

Polygon zkEVM vs. other ZK chains

Polygon zkEVM supports Ethereum EVM and uses ZK tests:

• Part of the Polygon ecosystem, shares POL token.
• Same taxation as general Polygon (see separate article).

Cross-chain via ZK: what is a ZK message?

Some bridges use ZK-proofs to verify cross-chain transactions (Layerzero, StarkGate):

• The ZK bridge is technically more secure than an optimistic bridge.
• Fiscally, the same treatment as any bridge: it is not a transfer if the ownership does not change.

Liquid staking in ZK ecosystems

zkSync and Starknet have their own liquid staking protocols:

• You deposit ETH → receive staking token → accumulate rewards.
• Same taxation as stETH on Ethereum (see liquid staking article).

Trading log on ZK-chains

• zkSync Explorer (explorer.zksync.io): Export transaction history.
• Starkscan (starkscan.co): For Starknet.
• Argent Wallet: Starknet native wallet with exportable history.
• Koinly: Support for zkSync Era and some Starknet features.

Summary: Key tax points for ZK-rollups

1. Airdrops of ZK, STRK and ecosystem project tokens are capital gains upon receipt.
2. Swaps, LP and lending in ZK-chains are taxed the same as in Ethereum L1.
3. The technical privacy of ZK-proofs does NOT exempt from tax obligations.
4. Records all bridge operations between L1 and ZK-chains.

Updated: April 2026 | Fiscal year: 2025