Due to vulnerability, DSA Keys (ssh-dss) have been deprecated and disabled in openssh7.0p1 by default, with the recommendation to update. Arch has provided notice.
“OpenSSH 7.0 and greater similarly disables the ssh-dss (DSA) public key algorithm. It too is weak and we recommend against its use. It can be re-enabled using the HostkeyAlgorithms configuration option:”
ssh -oHostKeyAlgorithms=+ssh-dss firstname.lastname@example.org
I couldn’t find if the latest version of busybox had updated for this, but the latest firmware on the EX4100 is showing openssh 5.0p1
OpenSSH_5.0p1, OpenSSL 1.0.1m 19 Mar 2015
Suggestion to update Openssl to 7.0p1
In the mean time, I will keep my ssh access to this NAS local.