Operation Hash

An operation hash (also known as a transaction hash or txid) is a unique, alphanumeric string generated by applying a cryptographic hash function—such as SHA-256 or Keccak-256—to the data of a blockchain operation. This hash serves as a permanent, tamper-evident identifier for that specific action, whether it's a token transfer, smart contract deployment, or a validator's attestation. It is the primary reference used to look up, verify, and track the status of an operation on a block explorer or within a node's mempool.

The creation of an operation hash is fundamental to blockchain integrity. When a user submits a transaction, the network's nodes hash its contents, including the sender's address, recipient, amount, and a nonce. This resulting hash is then signed with the sender's private key to create a digital signature, proving authorization. The signed transaction, with its hash, is broadcast to the network. Once validated and included in a block, the operation hash becomes an immutable part of the blockchain's history, allowing anyone to cryptographically verify that the transaction data has not been altered.

For users and developers, the operation hash is a critical tool. It is the key piece of information required to query a transaction's confirmation status, check for gas fees consumed, or debug a failed smart contract interaction. On networks like Ethereum, a transaction hash begins with 0x, while Bitcoin transaction IDs are typically 64 hexadecimal characters. It's important to distinguish an operation hash from a block hash (which identifies an entire block) and an address (which identifies an account).

In practice, operation hashes enable transparency and auditability. For example, providing a supplier with the hash for a payment proves the transaction was sent without revealing the payer's entire wallet history. In decentralized applications (dApps), front-ends use these hashes to poll for transaction completion and update user interfaces. The deterministic nature of hash functions also means that any change to the original transaction data—even a single character—would produce a completely different hash, immediately signaling tampering.

While primarily a lookup tool, the operation hash also plays a role in higher-level protocols. In layer-2 scaling solutions like Optimistic Rollups, transaction hashes from the main chain are used to prove the inclusion and correctness of bundled operations. Similarly, in cross-chain communication protocols, hashes are often used as unique identifiers to track asset transfers or message states across different blockchain environments, forming a core component of interoperability.

An operation hash is generated by serializing the complete data of a blockchain operation—including the sender's address, recipient, amount, gas parameters, nonce, and any encoded function calls—into a canonical byte sequence. This raw data is then processed by a cryptographic hash function, such as Keccak-256 (used by Ethereum) or Blake2b (used by Tezos), which produces a fixed-length alphanumeric string. This resulting hash serves as the operation's immutable and unique identifier on the network, essential for tracking its status and inclusion in a block.

The process is deterministic, meaning the same input data will always produce the identical hash. Before hashing, the operation data must be RLP-encoded (Recursive Length Prefix) on Ethereum or encoded using other protocol-specific serialization formats to ensure a consistent structure across all network nodes. This step is critical; even a single bit of difference in the input—such as changing the gas price by 1 wei—will result in a completely different hash, a property known as the avalanche effect. The hash is typically computed and signed by the user's wallet software before the operation is broadcast.

Once generated, the operation hash is used throughout the blockchain's lifecycle. Nodes and block explorers use it to reference the specific operation. In systems like Ethereum, the operation hash is distinct from a transaction hash; an operation can be a simple value transfer or a contract invocation, all hashed under the same scheme. This hash is also cryptographically linked to the block that includes it, as the block's Merkle root is derived from the hashes of all its contained operations, creating an unforgeable chain of proof.

In the User Operation flow, the operation hash (or userOpHash) is the deterministic identifier computed from the contents of a UserOperation struct. It is generated by hashing the operation's data along with the address of the entry point contract and the current chain ID, using the getUserOpHash function. This hash uniquely represents the intent of the transaction before it is included in a bundle and submitted to the blockchain, acting as a commitment to the operation's specific parameters.

This hash plays several critical roles. It is used by paymasters to sign their sponsorship agreement and by account contracts to validate signatures during the validateUserOp phase. Crucially, it also serves as the key for tracking the operation's state within the Entry Point's internal accounting, preventing replay attacks across different chains or entry point versions. The determinism of the hash ensures all parties—bundler, account, and paymaster—are referring to the exact same operation.

For developers and analysts, the operation hash is the primary reference point for querying transaction status, debugging failed operations, or analyzing mempool activity. Unlike a traditional transaction hash, which is assigned after mining, the userOpHash is known before submission, allowing for pre-execution validation and off-chain tracking. It is the linchpin that connects the off-chain components of the ERC-4337 system—the bundler, UserOperation mempool, and clients—with the on-chain execution via the Entry Point contract.