Sorry for my mistake. The HelloVerifyRequest in the previous email should be replace with "HelloRetryRequest".
On Mon, Dec 2, 2019 at 7:17 PM Xuan k <kxuan...@gmail.com> wrote: > Hi Ben, > > Thanks for your reply. But we understand may not be the same. > > Since ACK messages are not retransmitted, I think they should not consume > message_seqs. > If an ACK really use a message_seq and it is lost in network, new > handshake records will > always use a larger message_seq than the peer expected (next_receive_seq). > The peer will unable to continue the handshake process. > > And I think the ServerHello in the figure should start with 1, as the > figure shows. > The message_seq = 0 is used by HelloVerifyRequest, which is also been > processed by client > and been fed into its transcript hash function. > > So I think the HelloVerifyRequest should be counted and new ServerHello in > the figure > should start with message_seq = 1. > > Thanks, > > Zhai Zhaoxuan > > On Mon, Dec 2, 2019 at 3:54 PM Benjamin Kaduk <bka...@akamai.com> wrote: > >> That might be an artifact from Ack having at one point (the -00) been >> a handshake message. Though, it seems that the Server's message_seq >> space should also start at 0 with ServerHello, if I am understanding >> correctly. >> >> -Ben >> >> On Thu, Nov 28, 2019 at 03:15:38PM +0800, Xuan k wrote: >> > Hi Ekr, >> > >> > Thanks for your help. >> > >> > I have another question about the "message_seq" in section "6. Example >> of >> > Handshake with Timeout and Retransmission". >> > Could you please explain it? >> > >> > In the secion 6, the Client send message_seq = 0 in Record 0 and >> > message_seq = 2,3,4 in Record 2. >> > >> > Why message_seq = 1 is skipped by Client? >> > I think the ClientHello in the figure should begin with message_seq=1. >> The >> > message_seq = 0 is used by the first ClientHello which is the one >> without >> > cookies. >> > >> > >> > Thanks, >> > Zhai Zhaoxuan >> > >> > On 11/28/19 5:37 AM, Eric Rescorla wrote: >> > >> > >> > >> > On Tue, Nov 26, 2019 at 10:05 PM Xuan k <kxuan...@gmail.com> wrote: >> > >> > > Hi all, >> > > >> > > I'm trying to implement a DTLS1.3 library for embedded devices. But It >> > > seems something weird about retransmissions and ACKs. >> > > >> > > In the section "5.2. DTLS Handshake Message Format": >> > > >> > > The first message each side transmits in each association always >> has >> > > message_seq = 0. Whenever a new message is generated, the >> > > message_seq value is incremented by one. When a message is >> > > retransmitted, the old *message_seq value is re-used*, i.e., not >> > > incremented. From the perspective of the DTLS record layer, the >> > > retransmission is a new record. This record will have a *new* >> > > * DTLSPlaintext.sequence_number* value. >> > > >> > > >> > > In the section "7. ACK Message", the ACK message use the >> record_numbers >> > > (corresponds to *DTLSPlaintext.sequence_number*). >> > > >> > > For my understanding, the "message_seq" belongs to "Handshake" and the >> > > "sequence_number" or "record_numbers" belongs to >> > > record layer. >> > > >> > >> > Yes. >> > >> > The retransmission detection is done by "Handshake" using "message_seq", >> > > but the "acknowledge" is done by "record layer" using >> "record_numbers". >> > > It is so weird. >> > > >> > >> > Hmm... I don't think that this is particularly weird. This is, for >> > instance, how QUIC stream acknowledgement and retransmission works. >> > >> > >> > The retransmission, retransmission detection and acknowledge should be >> done >> > > in handshake process, but we need the record layer passing the >> > > record_numebrs to the handshake process. >> > > >> > > Since a new "sequence_number" is used for retransmission, we have to >> > > maintain a "record_numbers" to "message_seq" map with dynamic size. >> > > Each retransmission attempt creates a new relationship between a new >> > > "record_numbers" to an old "message_seq". >> > > >> > >> > Yes, that's how it works in NSS. >> > >> > >> > Since ACK is only used with Handshake messages, is it possible that we >> use >> > > "message_seq" in ACK messages? >> > > >> > Or we use *old* "sequence_number" for retransmission, >> > > >> > >> > Both of these give you strictly less information about the network. One >> of >> > the cool innovations in QUIC is to label each packet separately so you >> can >> > determine whether an ACK is an ACK of the original packet or a >> retransmit. >> > We are trying to inherit tha there >> > >> > -Ekr >> > >> > so we do not need maintain the dynamic map. And if replay detection is >> > > implemented, the retransmitted >> > > record can be dropped by record layer (by replay detection), the >> > > "Handshake Protocol" do not need to do retransmission detection. >> > > >> > > Thanks >> > > Zhai Zhaoxuan >> > > _______________________________________________ >> > > TLS mailing list >> > > TLS@ietf.org >> > > https://www.ietf.org/mailman/listinfo/tls >> > > >> >> > _______________________________________________ >> > TLS mailing list >> > TLS@ietf.org >> > https://www.ietf.org/mailman/listinfo/tls >> >>
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