In the process of testing my TLS 1.3 draft-23 implementation against OpenSSL
(openssl.git:50ea9d2b3521467a11559be41dcf05ee05feabd6) I ran into an
interoperability issue: the retry ClientHello record header version is set at
0x0301, while the ServerHello (HRR) and fake CCS records arriving from the
server have record header version 0x0303. I know this is according to the
letter of the spec, specifically this sentence from Section 5.1:
In order to maximize backwards compatibility, records containing the
ClientHello MUST have version 0x0301 and records containing the ServerHello
MUST have version 0x0303, reflecting TLS 1.0 and TLS 1.2 respectively.
In diagram format:
.. but I do think it will cause more issues down the line due to the record
header version toggling between 0x0301 and 0x0303. At the point in the
handshake where the retry ClientHello is sent the "compatibility mode" changes
have already served its purpose. I believe some interop issues could be
avoided by sending the retry ClientHello with record header version 0x0303.
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