| name | rng-crypto-specialist |
| description | Design, implement, and audit provably fair RNG and cryptographic seed workflows for casino games. Use when defining commit-reveal architecture, server/client seed lifecycle, nonce progression, hash/HMAC outcome derivation, bias-free range mapping, fairness transcript verification, or cryptographic release sign-off evidence. |
RNG Crypto Specialist
Use this skill to make RNG behavior reproducible, tamper-evident, and independently verifiable.
Workflow
- Define fairness contract before implementation.
- Specify game outcomes that are RNG-derived, transcript fields, and reveal timing.
- Set immutable rules for server seed rotation, client seed changes, and nonce increments.
- Declare what players can verify pre- and post-reveal.
- Choose cryptographic primitives and transcript schema.
- Prefer
SHA-256 commitments and HMAC-SHA256 outcome derivation unless the system requires otherwise.
- Store canonical transcript fields:
serverSeedHash, serverSeed (after reveal), clientSeed, nonce, gameId, mode, and outcome.
- Define exact string/byte serialization and encoding rules to avoid replay mismatches.
- Enforce bias-free outcome mapping.
- Derive randomness from deterministic crypto material only.
- Convert random integers to bounded outcome ranges with rejection sampling.
- Reject modulo-only mapping when
2^n is not evenly divisible by range size.
- Implement seed and nonce lifecycle controls.
- Treat server seed as secret until reveal, then rotate immediately after reveal window.
- Keep per-session or per-player nonce monotonic and gap-free.
- Block replay or out-of-order nonce acceptance at API boundaries.
- Verify transcripts with deterministic tooling.
- Recompute commitment hashes from revealed server seeds.
- Recompute expected outcomes from
serverSeed, clientSeed, and nonce.
- Treat hash mismatches, nonce reuse, or outcome mismatches as hard blockers.
- Produce cryptographic sign-off package.
- Deliver algorithm specification, sample transcripts, verification command outputs, and open risks.
- Include exact patch plan with file paths for any fixes.
Commands
python3 scripts/verify_provably_fair.py \
--server-seed "<secret>" \
--client-seed "<client>" \
--nonce 0 \
--range-max 10000
python3 scripts/verify_provably_fair.py \
--input <transcript.jsonl> \
--default-range-max 10000
Treat non-zero exits as blocker findings.
Output Contract
When handling RNG crypto tasks, return:
Protocol Summary: commit-reveal flow, primitives, serialization, and rotation policy.Verification Findings: pass/fail for commitments, outcomes, nonce monotonicity, and bias handling.Patch Plan: exact files/functions to change and why.Evidence: commands run and key outputs.Residual Risks: unresolved issues preventing sign-off.
References
references/workflow.md: end-to-end implementation and audit procedure.references/crypto-primitives.md: approved primitives, mappings, and pitfalls.references/signoff-template.md: concise report structure for handoff.
Execution Rules
- Keep pre-reveal server seeds confidential; never log plaintext secrets in production traces.
- Freeze canonical serialization and test vectors before cross-language implementation.
- Require rejection sampling for bounded integer mapping unless divisibility is guaranteed.
- Mark any unverifiable outcome path as non-compliant.
