[TLS] Record header size?

["Short, Todd" <[e-mail]>]

Apologies if this has been brought up before.

Has there been any consideration to changing the record header for encrypted traffic to be 4 bytes (i.e. 32-bits)? 5 bytes is a very awkward size, and some processors do not handle odd byte offsets well (it was a complaint I heard from Cisco router/switch engineers).

The latest TLS1.3 draft indicates that the record_version is deprecated and must be ignored. If TLSv1.3 is negotiated, then I propose that the record_version value must be { 4 } for encrypted records, making the version field is a single byte, such that the length of the record_header is reduced to 4 bytes.

Alternatively, a TLS extension could be added to negotiate the size of the record_header.

Yes, this creates a serious backwards compatibility issue, but if the record_version field is deprecated, then perhaps a change to the record_header could be made.

Thus:

   struct {
       uint8 major;
       uint8 minor;
   } ProtocolVersion;

   struct {
       ContentType type;
       ProtocolVersion record_version = { 3, 1 };    /* TLS v1.x */
       uint16 length;
       opaque fragment[TLSPlaintext.length];
   } TLSPlaintext;

   struct {
       ContentType opaque_type = application_data(23); /* see fragment.type */
       uint8 record_version = { 4 };    /* TLS v1.3 4-byte record header */
       uint16 length;
       aead-ciphered struct {
          opaque content[TLSPlaintext.length];
          ContentType type;
          uint8 zeros[length_of_padding];
       } fragment;
   } TLSCiphertext;

--
-Todd Short
// [e-mail]<mailto:[e-mail]>
// "One if by land, two if by sea, three if by the Internet."