On 29/10/2020 03:52, Thomas Antonio via openssl-users wrote: > Hello, how does openSSL determine the Record Layer Version used to > initiate a ClientHello message to the server? I believe the > determination is made at this level. > > When testing using multiple implementations (Python Requests on a Debian > machine and `cURL --tlsv1.2 --tls-max 1.2` from macOS) I will seemingly > at random see ClientHello messages using TLS Record Layer Version 1.0. > The TLS Handshake Protocol remains correctly set at 1.2. The majority of > the time the Record Layer Version is 1.2. What could be causing this > change in Record Version? > > I realize this is a valid message format and that a well configured TLS > 1.2 server will accept this. Just trying to get to the bottom of what is > causing this behaviour on the client side. > > A post showing the Record Version and Handshake Protocol mismatch is here > https://support.f5.com/csp/article/K53037818 The logic is here: https://github.com/openssl/openssl/blob/648cf9249e6ec60e0af50d5d903e05244b837cb0/ssl/record/rec_layer_s3.c#L860-L861 And here: https://github.com/openssl/openssl/blob/648cf9249e6ec60e0af50d5d903e05244b837cb0/ssl/record/rec_layer_s3.c#L882-L891 Basically the record version is never greater than TLSv1.2. If we're in an initial ClientHello (not a renegotiation or an HRR) and the max version is > TLSv1.0 then the record version is fixed at TLSv1.0 for the ClientHello record. Matt
