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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