Re: [TLS] DTLS 1.0 and DTLS 1.2 issues with retransmission

[Nikos Mavrogiannopoulos <[e-mail]>]

On Tue, Mar 8, 2011 at 3:00 PM, Eric Rescorla <[e-mail]> wrote:

>> If there is no answer to that, then a DTLS handshake would always require
>> a fixed amount of time (additional to calculations), e.g. 60 seconds -
>> if we take
>> the maximum time allowed for retransmission - to complete. That is because
>> I see protocol transition from
>> "handshake" -> "application data exchange"
>> only after handshake has been fully completed. Or is it implicit that
>> "draft-bmoeller-tls-falsestart-00" applies to DTLS? (in that case it
>> should be explicit).
>
> I don't think I understand the question.
> As soon as either side has *received* the last message it expects to
> get from the
> other side, it can start sending data.

Ok I think I got the point, but I don't think this is obvious.
What you are suggesting here is that a handshake such as:

Client                                  Server

ClientHello                  -------->
                                        ServerHello
                                        Certificate*
                                        ServerKeyExchange*
	                                CertificateRequest*
                             <--------  ServerHelloDone
Certificate*
ClientKeyExchange
CertificateVerify*
[ChangeCipherSpec]
Finished                     -------->
                                        [ChangeCipherSpec]
	                     <--------  Finished **lost**
                             <--------  Application Data
Certificate*
ClientKeyExchange
CertificateVerify*
[ChangeCipherSpec]
Finished                     -------->
                                        [ChangeCipherSpec]
	                     <--------  Finished **lost**
                             <--------  Application Data
                             <--------  Application Data
Certificate*
ClientKeyExchange
CertificateVerify*
[ChangeCipherSpec]
Finished                     -------->
                                        [ChangeCipherSpec]
	                     <--------  Finished
Application Data             <------->  Application Data

is valid for DTLS. My impression after reading draft-ietf-tls-rfc4347-bis-04
was that it is similar to TLS, in the sense that the handshake protocol
has to finish (for both parties) before application data are to be
exchanged (and
thus the above handshake would be invalid).



Something out of curiocity. Why was the handshake layer retransmission and
reassembly was preferred comparing to a retransmission and reassembly
layer at the
record protocol (for records exchanged during the handshake protocol)?

regards,
Nikos