Forcing wireshark to dissect null cipher TLS

asked 2021-09-09 14:26:55 +0000

eike
3 ●1 ●2

Hi,

we have a dissector for a custom protocol which can be the payload of TLSv1.2 packets with the cipher suite TLS_ECDHE_ECDSA_WITH_NULL_SHA (0xc006). The dissector is registered in lua with:

DissectorTable.get("tls.port"):add(49502, my_protocol)

These packages get dissected properly for connections, where the TLS handshake is part of the capture. When the handshake is missing wireshark does not dissect the application data of the tls packets.

Is it possible to tell wireshark to assume the that all TLS packages on a given port are not encrypted and to dissect them with the given dissector?

Kind regards and thank you. Eike

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answered 2021-09-09 19:03:23 +0000

André

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Without the handshake Wireshark does not know the size of the Message Authentication Code (MAC) and possibly padding. That is needed for a correct dissection.

A feature request can be done at https://gitlab.com/wireshark/wireshar...

In the past, before complete sessions with NULL ciphers were dissected, I had a similar issue and made a little modification in the upper layer protocol to simply skip the 5-byte Application Data header. That was good enough in my case.

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Thank you very much. Registering the dissector to TCP and skipping the first 5 bytes did the trick for me.

eike ( 2021-09-10 08:54:42 +0000 )edit

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Asked: 2021-09-09 14:26:55 +0000

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Last updated: Sep 09 '21

Forcing wireshark to dissect null cipher TLS edit