After upgrading a tunnel client hub to hub 7.92HF6, a hub-to-hub tunnel will fail to connect and the following error will be observed in the hub.log:
Aug 18 08:48:41:495  hub: SSL_connect error occured
Aug 18 08:48:41:495  hub:  error:0x14082174:SSL routines:ssl3_check_cert_and_algorithm:dh key too small
Aug 18 08:48:41:495  hub: TSESS could not connect to tunnel 126.96.36.199:443 (336077172)
Aug 18 08:48:41:495  hub: CTRL MergeProxy011-hub connection error: dh key too small (372)
Aug 18 08:48:41:495  hub: CTRL MergeProxy011-hub could not connect to server 188.8.131.52/443
Aug 18 08:48:41:500  hub: SSL_connect error occured
This is caused by an incorrect OpenSSL library that was bundled with hub 7.92HF5 and 7.92HF6.
For now, rolling back the hub to 7.92HF4 or prior will resolve the issue.
In the near future, a hotfix will be released for this issue.
Please check the UIM Hotfix Index Site - if you see a hotfix with a version higher than 7.92HF6, download that version and deploy it. (As of this writing, 8/22/2017, this has not been released but it is expected very soon.)