After enforcing TLSv1.2 on our internal Connections 5.5 servers the Files plugin would not work.
In the IHS logs I would see errors such as
[warn] [client 220.127.116.11] [7f9a700a7060]  SSL0222W: SSL Handshake Failed, No ciphers specified (no shared ciphers or no shared protocols). [xx.xx.xx.xx:62899 -> xxx.xxx.xxx.xxx:443] [09:45:11.000102454] 0ms
Enabling trace on IHS showed that the protocol being used was TLSv1.0 which matched Wireshark output. Oddly Status Updates and Activities plugins use TLSv1.2.
“GET /files/basic/api/library/4a7a7240-8f68-44d8-9447-7410cc2bb467/feed?pageSize=300&acls=true&sI=601 HTTP/1.1” 200 168770 TLS_RSA_WITH_AES_128_CBC_SHA TLSV1
I then had to allow TLSv1.0 until I could get an explanation from IBM.
Finally IBM came back with the following two lines to be added to the notes.ini.
Now in access_log I see TLSv1.2 being used.
“GET /files/basic/api/library/4a7a7240-8f68-44d8-9447-7410cc2bb467/feed?pageSize=300&acls=true&sI=601 HTTP/1.1” 200 168770 TLS_RSA_WITH_AES_128_GCM_SHA256 TLSV1.2
IBM also suggested that I check the following was set in plugin_customization.ini, which it was.
The notes.ini values have been pushed out to my colleagues via Domino policies.