Ream BlackBox Interop Testing for Post‑Quantum Lean Ethereum

The Ethereum Foundation video explains how Lean Ethereum is adopting hash‑based signatures, which create signing constraints that client software must maintain. Mohit Grover describes an EPF cohort 7 project that converts these constraints into black‑box integration tests in the Hive framework, beginning with the Ream client and targeting cross‑client coverage. The talk details the process of studying XMSS, exposing the production signer, independently verifying its output, and building tests for same‑slot conflicts, concurrent requests, restart persistence, and key activation and preparation boundaries. It also looks at signature aggregation and the difficulty of passing proof material between clients. The aim is to make failures reproducible and reveal coverage gaps beyond existing cryptographic unit tests.