CODEHASH

codeHash is a cryptographic fingerprint that identifies a piece of on-chain contract code. It represents the hash of the compiled Wasm bytecode of a contract and is stored in the blockchain’s code storage as a persistent, referenceable identifier. The concept is commonly used in platforms that separate contract code from contract instances, such as the Contracts module in Substrate-based networks.

When code is uploaded to the chain, the runtime computes the codeHash from the Wasm bytes and stores the code under that hash. A contract can then be instantiated by referencing the codeHash and supplying constructor parameters. Multiple contract instances can be created from the same codeHash, enabling code reuse. If the code needs to change, new code must be uploaded to produce a new codeHash.

Technical details vary by platform, but the hash is typically a 256-bit digest (for example, Blake2b-256 or equivalent) of the code payload. The code itself remains immutable at its codeHash; updating behavior requires a new codeHash and potentially new deployment.

Security and reliability considerations include ensuring the integrity of the code being hashed, guarding against accidental code changes, and recognizing that the hash does not capture deployment state or runtime data. CodeHash does not by itself verify correctness of the code; it simply serves as a fingerprint.

Related concepts include contract addresses, on-chain code storage, and platform-specific APIs for deploying and instantiating contracts. In Substrate and ink!-based environments, the codeHash is a central reference used during contract creation and code management.