I then used this site to check what encryption strength my machine supports:
It seemed my pc is configured to only allow 128 bit connection.
Luckily I have found this link which explains how to configure windows to use 256-bit Ssl (Vista only). It seems the problem is in the windows defaults and not in Wcf. This changed the result in IE:
and also the Wcf client worked. The strange is that the setting that needs to be changed should only affect the order of the supported algorithms. So if the server requires a 256-bit OR a 128-bit key, the default setting would suggest 128 first. But if the server only allows 256-bit I would expect this to work since this is a supported configuration, just not the first in order. Either way the fix made it work. What's next? get this blog rss updates or register for mail updates!