Receipt Proof

Brevis receipt proof attestation via zk-SNARKs enables efficient verification of any transactions' receipt (included in the synced blocks) that happened on a connected remote chain.
Similar to the storage slot value proof described in the previous section, receipt proof is also using the synced block header information stored on the destination chain as the ground truth. With this, one can prove the source chain's receipt information by proving the following parts:
  1. 1.
    validity of a block receipt root that matches the synced block header info;
  2. 2.
    validity of the receipt leaf hash that matches the receipt root.
The rest of this page outlines the mechanisms for implementing receipt proof attestation:


This circuit is composed of two parts, including MPT calculation and block header calculation.
Public Inputs (can be used by on-chain app contracts):
  • LeafHash Leaf node (receipt leaf node) key of the receipt MPT.
  • BlockHash Hash of the block which include this receipt.
  • BlockNumber Number of the block which include this receipt.
  • BlockTime Time of the block which include this receipt.
Private Inputs:
  • Key The key nibble of the receipt in MPT.
  • KeyLength The length of the key above.
  • RootHash Receipt MPT root hash.
  • KeyFragmentStarts The index for each node in key nibbles.
  • NodeRlp Node value for each node in the merkle branch.
  • NodeRlpRoundIndexes NodeRlp keecak round number.
  • NodePathPrefixLength Length for check node type in merkle branch.
  • NodeTypes MPT node type.
  • Depth MPT depth.
  • BlockHashRlp Block rlp.
  • BlockFieldsNum Block fields count.
  • BlockRoundIndex Block hash keccak count from block rlp.

Validate receipt root

The receipt root hash is one field of the block header RLP, which is used to calculate the block hash. The circuit first proves that the receipt root hash is included in the decoded block RLP, and then it computes the keccak hash of the block RLP to match the provided public input.

Validate receipt leaf

To prove the validity of the public input receipt leaf hash, the circuit uses the Merkel branch that includes the receipt leaf to compute the MPT root hash and verify that it matches the validated receipt root hash. Note that the circuit only validates the receipt leaf hash, leaving the validation of receipt RLP fields to the on-chain verifier contract.


Receipt Proof Circuit Verifier

The circuit verifier contract is generated by gnark verifier. The main process of this contract is to check the correctness of the proof by calculating the pairing on BN254 using Groth16.

Receipt Proof App Verifier

The ZK proof and metadata generated by the Brevis proofing system can be submitted to the ReceiptVerifier contract through the verifyReceipt function to get the ZK-attested slot value. Please refer to this section for smart contract usage.