On 02/19/2018 04:14 AM, Martin Thomson wrote: > (+tls@) > > This is a good question Jim and one that I thought through during > implementation, but failed to capture in the doc. > > Basically, there is no way to validate the extension if the client > includes an unknown version of TLS or an extension that it doesn't > understand. A client can know because it should understand the > protocol as negotiated. > > The text currently says "an endpoint MUST NOT send a value higher than > the protocol-defined maximum record size unless explicitly allowed by > such a future version or extension" I think that we should add "A > server MUST NOT enforce this restriction; a client might advertise a > higher limit that is enabled by an extension or version the server > does not understand." > > Does that make sense?
Mostly. I am not sure that that exact phrasing is great, though, as we do want the server to enforce the restriction *as written*, i.e., taking into account that the client may know better than the server if a newer version and/or extension is in use. So, maybe something like "Receiving a larger value is not necessarily cause for a server to abort the handshake, given this possibility". -Ben > > On Mon, Feb 19, 2018 at 5:51 PM, Jim Schaad <i...@augustcellars.com> wrote: >> I was looking at this document relative to a specific question for Kathleen, >> and I had one thing that I would like you to look at and see if you think it >> is clear enough. >> >> I have a server that is TLS 1.2, a client that is TLS 1.2 & 1.3. It sends >> a hello w/ and extension value of 2^14+1. It is not completely clear to me >> that the server should accept this as a legal value and compute the min of >> it and the maximum 1.2 value as the value to use when sending messages to >> the client rather than producing an error message because the value is too >> large. >> >> Jim >> >> > _______________________________________________ > 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