Hi Mike,

> I felt that I was unwelcome in this group by some of the "angry 
> cryptographers" as I call them.

No reason to worry. Luckily, we don't have any angry cryptographers in this 
group.

On top of what Richard mentioned in his response, take a look at Appendix D of 
the spec, see https://tools.ietf.org/html/rfc8446#appendix-D.

Ciao
Hannes

-----Original Message-----
From: TLS <[email protected]> On Behalf Of Michael D'Errico
Sent: Sunday, September 27, 2020 9:52 PM
To: [email protected]
Subject: [TLS] TLS 1.3 Problem?

Hi,

Took a quick look at RFC 8446 and noticed that there is no definition of 
ServerKeyExchange or ServerHelloDone which are part of TLS 1.2 and prior.  A 
1.3 client talking to a 1.2 or earlier server is likely going to receive both 
of these
messages:

RFC 5246                          TLS                        August 2008

       Client                                               Server

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

              Figure 1.  Message flow for a full handshake

Since RFC 8446 obsoletes RFC 5246, this is a serious problem.

How is this supposed to work?   Sorry but I did not follow the development of 
TLS 1.3.  I felt that I was unwelcome in this group by some of the "angry 
cryptographers" as I call them.

Mike

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