Cyrinx is a research prototype. It is not a hardened, audited secure communications product, and should not be relied on as one.

Please report security issues privately to david@weekly.org rather than opening a public issue. Include a description, reproduction steps, and the affected component (C core, Swift/Kotlin binding, or harness). We'll acknowledge receipt and work with you on a disclosure timeline.

• The optional crypto envelope (X25519 ECDH + CTR/HMAC) is opt-in and OFF by default. The PHY does not encrypt or authenticate by default. An application that needs confidentiality or integrity must explicitly enable the envelope and accept its throughput cost — near-free on fast MCS tiers (~0.15 %) but able to dominate goodput on the slow fallback tiers. See docs/CRYPTO_TRADEOFF.md for the per-MCS cost table.
• Acoustic links are inherently broadcast over the air: anyone within earshot (or with a microphone) can receive the signal. Confidentiality, if required, must come from the application layer, not the medium.
• The crypto envelope has not undergone independent cryptographic review. Treat it as experimental.