Version statement for TLS1.3 assigns 0x0301 (TLS1) and 0x0303 (TLS1.2)

[argyrisp]

In jarm.py, function packet_building(), while appending the first bytes together, this statement does not make sense to me:

if jarm_details[2] == "TLS_1.3":
    payload += b"\x03\x01"
    client_hello = b"\x03\x03"

If JARM is specified to use TLS1.3, the versions used are 0x0301 (TLS1) and 0x0303 (TLS1.2)? Shouldn't it be 0x0304? I've just started playing around with TLS so I might be missing some key information here.

[fragileeye]

As far as I understand, during the ClientHello phase, the record version does not need to match the ClientHello version. Since JARM does not really support TLS 1.3, setting the record version to 0x0301 is an optional configuration at this point. However, when the ClientHello is used for a TLS 1.3 request, it should be set to 0x0303, as per RFC 8446, section 4.1.2.