Each protocol has two kinds of enable/disable flags: "enabled" and "disabled by default". Those have different default values for each protocol and there are registry setting allowing to change each of them. Only "enabled" protocols are used at all. This patch limits "enabled" protocols to those that we can really support. If an application asks schannel to use default set of protocols (which I'd expect them to do unless they have a good reason), schannel will use all "enabled" protocols that are not "disabled by default". An alternative to default set of protocols is listing each allowed separately.
This means that if protocol is "enabled" and "disabled by default" it won't be used unless application explicitly asks for it. SSL2 is such a protocol by default. Do you think we should do this differently?