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On-Chain Tracking of ZK-Rollups
Osgur Murphy O Kane
Key Takeaways
5 min read
  • On-chain tracking will be possible for validity rollups such as Starknet and zkSync given that transaction data is maintained at L2.
  • Privacy-focused ZK-Rollups such as Aztec are designed to be encrypted so that only users with the requisite verification key can view the transaction details on the L2. This poses a risk to the ability to effectively track such L2 transactions on-chain.
  • L3s are currently hypothetical (validity rollup L2s aren’t properly live yet). However, privacy-focused L3s are expected to be extremely scalable with off-chain data availability. These will probably be untrackable.


Many so-called ‘ZK-Rollups’ are not ‘Zero-Knowledge’ e.g. zkSync, StarkNet, Polygon zkEVM. In fact, the transaction data is visible on-chain. A more accurate term is ‘Validity Rollups’.

Transaction execution occurs at L2, and transactions are finalized at L1 (leveraging security and decentralization of L1).

A proof is generated that attests to the validity of these transactions and the change of state. The rollup’s smart contract at L1 checks this proof, and if it is correct, the state is considered final.

There are 2 instances of ‘blocks’

  • At L2 (on validity rollups these include the individual transaction details) and
  • L1 rollup block (which verifies the validity of transactions computed at L2).