Re: http.sslVersion only specifies minimum TLS version, later versions are allowed

[Jeff King <peff@peff.net>]

On Mon, May 03, 2021 at 03:02:10PM +0000, Daniel Carpenter wrote:

> > Just looking at how the curl binary does it, "--tlsv1.2" means "1.2 or
> > greater" (which is not at all surprising; the library interface tends to
> > mirror their command-line and vice versa, and our behavior is influenced
> > by the library interface here).  But that implies to me that curl folks
> > considered this and though the "or greater" behavior was useful (which
> > makes sense -- the main goal is probably to avoid insecurities in older
> > versions of the protocol).
> > 
> > Anyway, the binary also has --tls-max for capping the maximum version.
> > That seems more flexible in general than "use this version exactly" (if
> > you only care that 1.3 is broken, then setting "max=1.2" lets you talk
> > to servers that support 1.1 or 1.2).
> > 
> > -Peff
> 
> I agree that the current behaviour is better for most users, and that
> some kind of separate "max" config option would work for anyone in my
> situation.
> 
> Another idea would be to keep the current behaviour for
> `http.sslVersion`, but use an exact match with the environment
> variable only. That already takes priority, and I imagine its main
> appeal over the config option is for users that want to try something
> with a specific TLS version.

I think you're right that it may work for many people, but I'd shy away
from it simply because it's subtle and hard to explain.

Adding config and environment variables for "max" is pretty
straight-forward to explain. I think it would also make sense to improve
the documentation for http.sslVersion to make it clear that this is a
minimum (the current wording is quite misleading).

-Peff