[TLS] SCSV versioning

[🔓Dan Wing <[e-mail]>]

I recently became aware that Microsoft IE won't implement SCSV.  Near as I can tell, this is the main concern, but it is not terribly detailed about the concern:


https://connect.microsoft.com/IE/feedback/details/1002874/internet-explorer-should-send-tls-fallback-scsv

> One of the developers pointed out that the TLS_FALLBACK_SCSV feature has a significant downside-- because it doesn't convey any specific version information, it becomes a general "never fall back" signal. The problem is that such signals are too broad; fallbacks were only ever introduced because servers often use TLS stacks with implementation bugs. Any "don't fallback" signal sent by such a server will be very bad for compat.
> 
> Now, the counterargument is that servers should just implement TLS properly and update when new versions are released and/or bugs are found, but there's strong precedent showing that this just doesn't happen. IE's decade long "DocumentMode/CompatibilityView" fiasco comes from the fact that there was a single "StandardsMode" flag that the majority of pages had opted-into without actually being standards compliant.


Has this concern been discussed in the working group?  Should we resolve this?  (I think a resolution might be along the lines of "I have previously tried 1.2 and 1.1", but really depends on one's interpretation of the 'significant downside' concern that an IE developer has.)


Yes, I know SCSV has finished WG review and IESG review.

-d