nx_tls13_hello.nx

nx_tls13_hello.nx -- TLS 1.3 ClientHello + ServerHello (RFC 8446 §4.1.2 / §4.1.3). Phase 0b §F.2 of the Nishi TLS 1.3 stack per docs/NISHI_TLS13_GAP_AUDIT.md. Composes the extension emitters from nx_tls13_ext into a complete ClientHello byte stream that can go on the wire. Parses an incoming ServerHello into its fixed-position fields + an extensions blob the caller iterates. Both Hello structures sit inside a 4-byte Handshake wrapper: struct { HandshakeType msg_type; /* 1 byte: 1=ClientHello, 2=ServerHello */ uint24 length; /* 3 bytes, body length */ <ClientHello | ServerHello body>; } Handshake; ClientHello body (RFC 8446 §4.1.2): ProtocolVersion legacy_version = 0x0303; Random random; (32 bytes) opaque legacy_session_id<0..32>; (1-byte len + bytes) CipherSuite cipher_suites<2..2^16-2>; (2-byte len + 2-byte suite ids) opaque legacy_compression_methods<1..2^8-1>; (1-byte len + bytes, always 0x01 0x00) Extension extensions<8..2^16-1>; (2-byte len + emitted extensions) ServerHello body (RFC 8446 §4.1.3): ProtocolVersion legacy_version = 0x0303; Random random; (32 bytes) opaque legacy_session_id_echo<0..32>; CipherSuite cipher_suite; (2 bytes; single, not list) uint8 legacy_compression_method; (always 0) Extension extensions<6..2^16-1>; What it does today: - emit ClientHello with all 5 minimum-credible extensions (SNI, supported_versions, supported_groups, signature_algorithms, key_share) in the canonical order - parse ServerHello fixed fields + return extensions blob - iterate an extensions blob, find one by extension_type