On Wed, Nov 23, 2016 at 3:39 AM, Andreas Walz <andreas.w...@hs-offenburg.de> wrote:
> Dear all, > > bringing up this thread again .... > > In the course of studying the way TLS implementations treat the "version" > (or "legacy_record_version") field in the record header, we were wondering > (please excuse if we missed some arguments here from past discussions): > > (1) What is an implementation (in particular when receiving the first > bytes over a new connection) supposed to do if the record's version field > signals a protocol version the implementation does not support? I > understand that, at this stage, enforcing a specific value (e.g. 0x0301 > according to the TLSv1.3 draft) is detrimental to interoperability. > However, if that field bears any meaning (in either TLSv1.3 or previous > versions), what is it? I would expect this field is supposed to allow > signaling a potentially non-backward compatible record format > (inauspiciously interfering with a receiver disregarding the record > version). Provided this field isn't treated as an enum, what about > checking/enforcing at least the major version as BoringSSL does (as far as > I know)? In any case, I would propose to be very clear about this in the > text (my sense was that there is some work in progress, but I couldn't find > anything). In implementations (<TLSv1.3), we found all kinds of > interpretations. > In general, it should ignore it. It's going to become increasingly common to have this be a version you don't support given the recommendation to use 0301 and the ongoing deprecation of TLS 1.0. I think it would be fine to sanity check the major version, but I'm not sure what would be gained by requiring this. > (2) What is an implementation (up to TLSv1.2, as the TLSv1.3 spec is > rather clear about that) supposed to use for the record's protocol version > field before a version has been agreed upon (e.g. when sending an alert > after receiving an unparsable ClientHello)? My best guess would be to set > it to the lowest (TLS) protocol version that uses the same record format > (probably 0x0301). However, we observe several servers which, in such > cases, answer with an alert with weird record protocol version values, e.g. > 0x0000.] > Yes, this seems like a reasonable procedure. Not sure how to tell TLS 1.2 impls what to do at this point, though. -Ekr > > Thanks and Cheers, > Andi > > ___________________________________ > > Andreas Walz > Research Engineer > Institute of reliable Embedded Systems and Communication Electronics > (ivESK) > Offenburg University of Applied Sciences, 77652 Offenburg, Germany > > > > >>> Benjamin Kaduk <bka...@akamai.com> 11/10/16 5:22 PM >>> > On 11/08/2016 06:25 PM, Martin Thomson wrote: > > On 9 November 2016 at 05:59, Brian Smith <br...@briansmith.org> > <br...@briansmith.org> wrote: > > This isn't a pervasively shared goal, though. It's good to let the browsers > police things if they want, but I think a lot of implementations would > prefer to avoid doing work that isn't necessary for interop or security. > > If you permit someone to enforce it, then that is sufficient. I don't > think that we should ever force someone to enforce these sorts of > things (as you say, sometimes strict enforcement isn't cheap or even > desirable). > > > Agreed. We should probably change the text a bit, though, as right now > readers can get two different readings depending on whether they go for a > strict decode_error (or illegal_parameter?) since the struct doesn't match > the definition, or follow the "MUST be ignored for all purposes". > > -Ben > > _______________________________________________ > TLS mailing list > TLS@ietf.org > https://www.ietf.org/mailman/listinfo/tls > >
_______________________________________________ TLS mailing list TLS@ietf.org https://www.ietf.org/mailman/listinfo/tls
