Hi Nikos, Hannes & Thomas,
This ConnectionID concept is really a useful feature for a client node which
faces a change in transport and network layer. I am having few suggestions in
the proposed draft, which are listed below.
1) In section 3 of this draft, explains about the modification in
"DTLSCiphertext" structure. I feel instead of modifying existing DTLS and TLS
record header, we can directly introduce a new record type (ContentType) for
app data (application_data_with_cid(25)). For this new record type, we can
propose a modified record header for both TLS and DTLS.
2) More over section 3 says modification only in "DTLSCiphertext", not for
"TLSCiphertext". I hope this CID mechanism should be used for both TLS and
DTLS. Because this transport layer change problem is there for TLS based
applications (HTTPS) also in Smartphone(when it switches from Wifi to LTE). But
this TLS application problem is solved by MPTCP, but I dont think all
webservers are supporting this MPTCP. So I feel CID is required for both TLS
and DTLS.
3) As part of defining new record type, we can remove some unused fields like
version, epoch. After removing epoch we can mandate that both entity should
not start renegotiation. Sample design for new record header with CID is
mentioned below
struct {
uint8_t ContentType;
uint8_t CID_len;
CID cid; /* Length varies from 4 to 8 (or 16) */
uint48 sequence_number;
uint16_t record_length;
} DTLSRecordHeader;
opaque CID <4..8>;
struct {
uint8_t ContentType;
uint8_t CID_len;
CID cid; /* Length varies from 4 to 8 (or 16) */
uint16_t record_length;
} TLSRecordHeader;
opaque CID <4..8>;
4) Another option is we can keep CID_len as 4 bit to represent a CID of size.
And this 4 bit can be placed in the MSB of the CID field.
....
uint8_t CID_len:4;
CID cid; /* Length varies from 28bit to 60 bit (or 124bit) */
....
5) Section 3.1 and 3.2 talks about the new extensions for negotiating this
feature support. But I feel no need of new extensions to negotiate this, we can
make client to add new SCSV cipher in its cipher list. If server accepts then
after handshake the first application data send by server should be of type
application_data_with_cid(25), which should hold the new record header with
CID. The same CID should be used by client in the further messasge. If client
sends the 1st application data after handshake, then it can send application
data with default record type (application_data(23)). If the first application
data record received from server is not of application_data_with_cid(25) means
client should understand that server has not accepted the SCSV proposed. And
client should continue app transfer with default record type
(application_data(23)).
Please provide your comments on this suggestion.
Regards,
Ashok
________________________________
[Company_logo]
Raja Ashok V K
Huawei Technologies
Bangalore, India
http://www.huawei.com
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