nx_tls13_record.nx

nx_tls13_record.nx -- TLS 1.3 record-layer protection (RFC 8446 §5.2). Phase 0b §K of the Nishi TLS 1.3 stack per docs/NISHI_TLS13_GAP_AUDIT.md. The bridge between the shipped ChaCha20-Poly1305 AEAD primitive and the actual TLS wire format. Every encrypted record on a TLS 1.3 connection -- handshake or application data, in either direction -- flows through this. Record wire format (RFC 8446 §5.1, §5.2): struct { ContentType type = 23; // application_data wrapper ProtocolVersion legacy_version = 0x0303; uint16 length; // total of AEAD output opaque encrypted_record[length]; // AEAD output (CT || tag) } TLSCiphertext; Inner plaintext (what AEAD encrypts): struct { opaque content[TLSPlaintext.length]; ContentType type; // the REAL content type uint8 zeros[padding_length]; // optional padding } TLSInnerPlaintext; Nonce construction (RFC 8446 §5.3): nonce = pad_left(seq_num, iv_len) XOR static_iv where static_iv is the per-direction traffic_iv derived from nx_tls13_schedule. seq_num is a 64-bit counter; for IV length 12 (ChaCha20-Poly1305 + AES-GCM), the left-pad is 4 zero bytes. AAD construction (RFC 8446 §5.2): additional_data = TLSCiphertext header (the 5 bytes: type + legacy_version + length) What it does today: - encrypt: construct inner plaintext, derive nonce, encrypt+tag