On Friday, 2 September 2016 18:53:45 CEST David Benjamin wrote: > I've finally gotten to uploading > https://tools.ietf.org/html/draft-davidben-tls-grease-01 which hopefully > resolves the procedural issues (thanks again!). I've also revised the text > slightly after some off-list feedback about the risks of non-deterministic > failures.
Clients SHOULD balance diversity in GREASE advertisements with determinism. For example, a client which randomly varies GREASE value positions for each connection may only fail against a broken server with some probability. This risks the failure being masked by automatic retries. A client which positions GREASE values deterministically over a period of time (such as a single software release) stresses fewer cases but is more likely to detect bugs from those cases. How about adding "In particular, it is RECOMMENDED that for a given browsing session, used GREASE values for a given server are constant."? Clients MUST reject GREASE values when negotiated by the server. When processing a ServerHello containing a GREASE value in the ServerHello.cipher_suite or ServerHello.extensions fields, the client MUST fail the connection. When processing an ECParameters structure with a GREASE value in the ECParameter.namedcurve field, the client MUST fail the connection. Note that this requires no special processing on the client. Clients are already required to reject unknown values selected by the server. Don't the other RFCs just say that clients should reject values not advertised by client? Since GREASE values are advertised by clients, I don't think the "no special processing" applies. As such, handling how connections in which server selects GREASE values should be specified precisely. (I haven't checked the RFCs for that so I may be mistaken, but still is a bit dicey to say that programmers don't need to check error handling in their code...) -- Regards, Hubert Kario Senior Quality Engineer, QE BaseOS Security team Web: www.cz.redhat.com Red Hat Czech s.r.o., Purkyňova 99/71, 612 45, Brno, Czech Republic
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