Module commitment 

Hash-based commitment scheme.

A commitment protocol has two phases:

1. Commit: the sender picks random r and computes C = H(r || m). They send C to the receiver. C reveals nothing about m (hiding) and the sender can’t later claim a different m' (binding).

2. Reveal: the sender sends (r, m). The receiver checks H(r || m) == C.

Used in threshold signing nonce rounds: each party commits to their nonce before any party reveals, preventing last-minute adaptive attacks.

Structs

Commitment

A commitment: hash of (randomness || value).

Decommitment

The decommitment: randomness + value needed to open a commitment.