nx_tls13_auth.nx

nx_tls13_auth.nx -- TLS 1.3 auth-related handshake message parsers. Phase 0b §H of the Nishi TLS 1.3 stack per docs/NISHI_TLS13_GAP_AUDIT.md. Pure-byte parsers for the three server-side handshake messages that follow ServerHello in a TLS 1.3 1-RTT flow: 1. EncryptedExtensions (RFC 8446 §4.3.1) Just an extensions blob; carries server-side extensions that the spec wants encrypted (max_fragment_length, ALPN pick, etc.). 2. Certificate (RFC 8446 §4.4.2) certificate_request_context: opaque<0..255> (1 byte len) certificate_list: per entry: opaque cert_data<1..2^24-1> (3 byte len) Extension extensions<0..2^16-1> (2 byte len) 3. CertificateVerify (RFC 8446 §4.4.3) SignatureScheme algorithm (2 bytes) opaque signature<0..2^16-1> (2 byte len) All three sit inside the standard Handshake wrapper (msg_type + uint24 length). This module does NO cryptographic validation -- signature verification, cert chain validation, hostname matching all live in Gap I (nx_x509_validate, queued). Here we just turn bytes into structure offsets the caller can hand to the verifier. What it does today: - parse EncryptedExtensions; expose extensions blob offsets - parse Certificate; expose FIRST cert's DER bytes + extensions offsets (most TLS 1.3 deployments use a 1-3 cert chain; iterating beyond the first is queued) - parse CertificateVerify; expose scheme + signature offsets - sealed verdict on every failure path What it doesn't do yet: - iterate every cert in chain (caller can re-call into the chain after the first; tls13_parse_certificate_chain_at queued)