17.2 TLS record layer

The TLS record layer partitions data to be transmitted into TLSPlaintext records of up to 2¹⁴ bytes. The data structure of a TLS 1.3 TLSPlaintext record is shown in Listing 17.1.

Listing 17.1: Structure of TLSPlaintext records

enum {
   invalid(0),
   change_cipher_spec(20),
   alert(21),
   handshake(22),
   application_data(23),
   (255)
} ContentType;

struct {
   ContentType type;
   ProtocolVersion legacy_record_version;
   uint16 length;
   opaque fragment[TLSPlaintext.length];
} TLSPlaintext;

The legacy˙record˙version variable denotes the record’s TLS version. As of TLS 1.3, legacy˙record˙version is deprecated, and the only requirement in the TLS 1.3 specification is for this field to have the value 0x0303 for all records, except the initial ClientHello, which may also...