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openssltls1.3

configure psk_ke (PSK-only) mode in TLS1.3

I am using openssl 1.1.1 and trying to configure psk_ke (PSK-only) mode only in requests generated through s_client. In my requests, in client hello message, I am not able to suppress psk_dhk_ke mode, which I think is getting added by default.

I have used directive -allow_no_dhe_kex in s_client requests. It is only helping to get the psk_ke mode added in the packet.

Also the options like ec_point format, key share, signature algorithms are added in the client hello message which I think is due to psk_dhk_ke option included in client hello. Please correct my understanding if I am wrong.

Can psk_dhe_ke be suppressed in client hello along with ec_point format, key share, signature algorithms?

TCP dump of TLS1.3 client hello message:

Solution

  • It is not currently possible to suppress psk_dhe_ke with OpenSSL when using TLSv1.3. The "-allow_no_dhe_kex" option only allows the peer to select the no-dhe version, but doesn't suppress sending the dhe option.

    It is possible to suppress the ec_point_formats, signature_algorithms and key_share extensions in OpenSSL under certain circumstances - but not if you plan to do TLSv1.3. If you want to do TLSv1.3 then they will always be sent.