#101
ProposedPlutus

Integration of keccak256 into Plutus

Created on  by Sergei Patrikeev,  and Iñigo Querejeta-Azurmendi

Abstract

This CIP proposes an extension of the current Plutus functions to provide support for the keccak256 hashing algorithm, primarily to ensure compatibility with Ethereum's cryptographic infrastructure.

Motivation: why is this CIP necessary?

The integration of the ECDSA and Schnorr signatures over the secp256k1 curve into Plutus was a significant step towards interoperability with Ethereum and Bitcoin ecosystems. However, full compatibility is still impossible due to the absence of the keccak256 hashing algorithm in Plutus interpreter, which is a fundamental component of Ethereum's cryptographic framework:

  • data signing standard EIP-712,
  • keccak256 is the hashing algorithm underlying Ethereum's ECDSA signatures.
  • EVM heavily depends on keccak256 for internal state management

Adding keccak256 to Plutus would enhance the potential for cross-chain solutions between Cardano and EVM-based blockchains.

A compelling integration that would greatly benefit from keccak256 support on the Cardano blockchain is Hyperlane. Hyperlane is a permissionless interoperability layer that facilitates communication of arbitrary data between smart contracts across multiple blockchains. Hyperlane's interchain security modules rely on the verification of specific cryptographic proofs from one chain to another. These proofs utilize the keccak256 hash to calculate consistent cross-chain message IDs. The multi-signature module verifies that a majority of off-chain validators have signed an ECDSA signature over a keccak256 digest, a common practice in EVM.

While Hyperlane can support different cryptographic primitives for non-EVM chains, doing so could compromise censorship resistance, resulting in only limited support for Cardano in Hyperlane. By implementing this CIP, Cardano could fully integrate with Hyperlane's security modules, enabling Cardano smart contracts to communicate with any blockchain supported by Hyperlane.

Specification

This proposal aims to introduce a new built-in hash function keccak_256.

This function will be developed following the keccak256 specification and will utilize the cryptonite implementation. Since cryptonite is already a part of the cardano-base, this simplifies its integration into Plutus. The cost of the keccak_256 operation will scale linearly with the length of the message.

More specifically, Plutus will gain the following primitive operation:

  • keccak_256 :: ByteString -> ByteString

The input to this function can be a ByteString of arbitrary size, and the output will be a ByteString of 32 bytes. Note that this function aligns with the format of existing hash functions in Plutus, such as blake2b_256

Rationale: how does this CIP achieve its goals?

While the keccak256 function might be implemented in on-chain scripts, doing so would be computationally unfeasible.

The library, cryptonite, is not implemented by and under control of the Plutus team. However,

  • It is a library already used in the Cardano stack to expose SHA3, and can be considered as a trustworthy implementation.
  • The function does not throw any exceptions as hash functions are defined to work with any ByteString input. It does not expect a particular particular structure.
  • It's behaviour is predictable. As mentioned above, the cost of the function is linear with respect to the size of the message provided as input. This is the same behaviour that other hash functions exposed in plutus (blake, sha3) have.

Path to Active

This CIP may transition to active status once the Plutus version containing the keccak_256 function is introduced in a node release and becomes available on Mainnet.

Acceptance Criteria

  • A Plutus binding is created for the keccak256 function and included in a new version of Plutus.
  • Integration tests, similar to those of the existing Plutus hash functions, are added to the testing infrastructure.
  • The function is benchmarked to assess its cost. As for other hash functions available in Plutus (blake2b and sha256), we expect the cost of keccak to be linear with respect to the size of the message. The Plutus team determines the exact costing functions empirically.
  • The ledger is updated to include new protocol parameters to control costing of the new builtins.

Implementation Plan

The Plutus team will develop the binding, integration tests, and benchmarks. The E2E tests will be designed and implemented collaboratively by the testing team, the Plutus team, and community members planning to use this primitive.

This CIP is licensed under [Apache-2.0][https://www.apache.org/licenses/LICENSE-2.0].