This happens on a fresh Leap 42.3 VM created in OpenStack using the Leap 42.3
image from [1]

$ zypper ref
...
$ zypper in salt
Loading repository data...
Warning: Repository 'openSUSE-Leap-42.3-Update' appears to be outdated.
Consider using a different mirror or server.
Warning: Repository 'openSUSE-Leap-42.3-Update-Non-Oss' appears to be outdated.
Consider using a different mirror or server.
Reading installed packages...
Resolving package dependencies...

Problem: nothing provides libsodium.so.13()(64bit) needed by
libzmq5-4.1.2-6.1.x86_64
 Solution 1: do not install python-pyzmq-15.2.0-3.2.x86_64
 Solution 2: break libzmq5-4.1.2-6.1.x86_64 by ignoring some of its
dependencies

Choose from above solutions by number or cancel [1/2/c] (c): c

$

Also, the "repository appears to be outdated" warnings seem strange given that
I ran "zypper ref" just seconds before.

[1]
http://download.opensuse.org/repositories/Cloud:/Images:/Leap_42.3/images/openSUSE-Leap-42.3-OpenStack.x86_64.qcow2