Re: [TLS] RFC 6066 - Max fragment length negotiation

[Martin Thomson <[e-mail]>]

On 17 March 2017 at 11:22, Peter Gutmann <[e-mail]> wrote:
> Is that from actually trying it with clients, or just assuming that
> implementations will do what the spec says?

I know for certain that NSS explodes.  Not from trying, but from
knowing that part of the code very well.  I'm fairly certain that
boringSSL does too, knowing David.

You say negative utility, but I've found that if you can get away with
stricter policing of these things, it helps prevent servers from
starting to do the wrong thing.  The odds that someone tests a new
server implementation against major browsers is fairly good.

In any case, what would you expect a client to do if they don't
advertise the extension?  In this case, max_fragment_length is so
badly designed that you can actually argue that it has utility, but I
don't consider that as a good argument for the general case.