Don't take our word for the result. Recalculate it.

#!/usr/bin/env python3
"""Gamwiz compatible provably fair verifier.

Runs locally with Python's standard library. This file makes no network calls.
It checks one HMAC-SHA256 calculation format only; other formats need their own verifier.
"""

import hashlib
import hmac

SERVER_SEED_HEX = ""
SERVER_SEED_HASH = ""
CLIENT_SEED = ""
NONCE = "0"
LABEL = ""
MODULO = "6"
RECORDED_OUTCOME = ""


def required(value: str, prompt: str) -> str:
    return value.strip() or input(prompt).strip()


server_seed_hex = required(SERVER_SEED_HEX, "Server seed (hex): ")
server_seed_hash = SERVER_SEED_HASH.strip()
client_seed = required(CLIENT_SEED, "Client seed: ")
nonce = int(required(NONCE, "Nonce: "))
label = required(LABEL, "Game label: ")
modulo = int(required(MODULO, "Modulo: "))
server_seed = bytes.fromhex(server_seed_hex)
if not server_seed:
    raise ValueError("Server seed is missing")
if nonce < 0:
    raise ValueError("Nonce must be zero or greater")
if modulo <= 0:
    raise ValueError("Modulo must be greater than zero")

computed_hash = hashlib.sha256(server_seed).hexdigest()
if server_seed_hash:
    commitment_matches = hmac.compare_digest(
        computed_hash.lower(), server_seed_hash.lower()
    )
    print("Commitment:", "MATCH" if commitment_matches else "MISMATCH")
else:
    print("Commitment: NOT CHECKED (server seed hash was not supplied)")

space = 2 ** 64
limit = (space // modulo) * modulo
counter = 0
while True:
    message = f"{client_seed}:{nonce}:{label}:{counter}".encode("utf-8")
    digest = hmac.new(server_seed, message, hashlib.sha256).digest()
    window = int.from_bytes(digest[:8], "big")
    if window < limit:
        pointer = window % modulo
        break
    counter += 1

outcome = pointer + 1
print("Computed server seed hash:", computed_hash)
print("Pointer (zero-indexed):", pointer)
print("Outcome (one-indexed):", outcome)

if RECORDED_OUTCOME:
    recorded_outcome = int(RECORDED_OUTCOME)
    print(
        "Recorded outcome:",
        "MATCH" if recorded_outcome == outcome else "MISMATCH",
        f"({recorded_outcome})",
    )
else:
    print("Recorded outcome: NOT CHECKED")