rng-crypto-specialist

RNG Crypto Specialist

Use this skill to make RNG behavior reproducible, tamper-evident, and independently verifiable.

Workflow

1. 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.

1. 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.

1. 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.

1. 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.

1. 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.

1. 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:

1. Protocol Summary: commit-reveal flow, primitives, serialization, and rotation policy.
2. Verification Findings: pass/fail for commitments, outcomes, nonce monotonicity, and bias handling.
3. Patch Plan: exact files/functions to change and why.
4. Evidence: commands run and key outputs.
5. 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.