Cairo EVM Utilities

This package provides a set of Cairo modules for interacting with Ethereum-compatible calldata and cryptographic primitives. It is designed to ease interoperability between Starknet and Ethereum by providing utilities for:

• Decoding EVM calldata
• Computing function selectors (EVM-style)
• Verifying Ethereum secp256k1 signatures

Package Structure

packages/evm/
├── decoder.cairo     # EVM calldata decoding logic
├── selector.cairo    # Function selector (keccak-based) computation
├── signature.cairo   # Ethereum signature verification & address recovery

📦 Modules

1. decoder.cairo — EVM Calldata Decoder

This module provides type-aware decoding of Ethereum-style calldata into felt252 spans.

• Decodes:
  • Static types: uint, int, address, bool
  • Dynamic types: bytes, string, dynamic arrays
  • Composite types: tuple, fixed bytes, function selector
• Handles dynamic offset resolution in calldata
• Returns Span<felt252>

let types = array![EVMTypes::Uint(256), EVMTypes::Array].span();
let decoded: Span<felt252> = ctx.decode(types);

2. selector.cairo — Keccak Function Selector

This module computes EVM-style function selectors based on a hashed function signature.

• Applies Keccak-256 to a byte-encoded function signature
• Returns the first 4 bytes (most significant, big-endian) as felt252

let data: ByteArray = "transfer(address,uint256)";
let selector_value = SelectorTrait::compute_selector(data);

3. signature.cairo — Ethereum Signature Verification

This module enables signature validation and address recovery from Ethereum secp256k1 signatures, using Cairo's native secp256k1 implementation.

• Verifies r, s, and v (y_parity) signature format
• Recovers public key and computes Ethereum address
• Compares against the expected signer

let sig = Signature { r, s, y_parity };
verify_eth_signature(msg_hash, sig, expected_eth_address);

🛠 Requirements

Make sure to import the relevant modules in your own contract/project:

use alexandria_evm::decoder;
use alexandria_evm::selector;
use alexandria_evm::signature;