Support for TLS_FALLBACK_SCSV

[johansglock]

Support for TLS_FALLBACK_SCSV

[4a6f656c]

For the time being, we're going to hold off on bringing TLS_FALLBACK_SCSV support in - if we do end up adding support for it, we will do it after further consideration and avoid rushing it in. If we decide to pull this in I'll take a closer look at your diff.

TLS_FALLBACK_SCSV is only useful in the case where a client willingly chooses to do a downgrade and attempts to establish a second connection at a lower protocol after the previous one unexpectedly failed. In short, the client should not do this - client-side fallback is dangerous ("a landmine" to quote agl). TLS_FALLBACK_SCSV only works if both ends support it and it is largely a case of adding a workaround to support/enforce insecure behaviour. Unless you control both ends, you cannot be sure TLS_FALLBACK_SCSV is available and if you do control both ends you can either force TLS 1.2 and/or avoid client-side downgrade.

[cypres]

I'm just gonna note that TLS_FALLBACK_SCSV support is now required for SSL Labs A+ rating, and that TLS_FALLBACK_SCSV is supported by both Chrome 33+ and Firefox 35+.
Server admins wanting to support this feature is then required to use ie. OpenSSL or BoringSSL.

I get why client-side fallback is dangerous, and in a perfect world clients and servers would use tls version negotiation to agree on a version, but sadly this is not the case with browsers as-is.
So for all us server admins out there, dealing with HTTPS, and wanting to provide the best possible security for the browsers we don't control, I urge you to add support.

[longsleep]

+1 to add support. I would like to see A+ results for LibreSSL powered servers again.

[bob-beck]

Based on their replies, I don't think I would grant that rating too much
credence - the people in charge of it seem more concerned with the A+
rating meaning "it supports all the features" - as they don't appear to be
willing to discuss the issues of the fact that FALLBACK_SCV isn't standard
yet, and has
some serious potential problems.

On Tue, Dec 23, 2014 at 9:50 AM, Simon Eisenmann [email protected]
wrote:

+1 to add support. I would like to see A+ results for LibreSSL powered
servers again.

Reply to this email directly or view it on GitHub
#36 (comment)
.

[4a6f656c]

Server-side TLS_FALLBACK_SCSV support has reluctantly been added to LibreSSL.