> On May 16, 2017, at 11:23 AM, Eric Rescorla <e...@rtfm.com> wrote: > > > > On Tue, May 16, 2017 at 8:17 AM, Russ Housley <hous...@vigilsec.com > <mailto:hous...@vigilsec.com>> wrote: > >> On May 15, 2017, at 7:01 PM, Eric Rescorla <e...@rtfm.com >> <mailto:e...@rtfm.com>> wrote: >> >> >> >> On Mon, May 15, 2017 at 12:38 PM, Russ Housley <hous...@vigilsec.com >> <mailto:hous...@vigilsec.com>> wrote: >> Just commenting on Section 4.2 … >> >> > >> > > 3. Section 4.2. >> > > >> > > "In general, detailed certificate validation procedures are out of >> > > scope for TLS (see [RFC5280]). This section provides TLS-specific >> > > requirements." >> > > >> > > I don't see an explanation of why it is out-of-scope. The reference >> > > is just to RFC5280, which seems odd. I would expect the reference to >> > > be to something that explains why it is out-of-scope. >> >> I think the the separation of certificate path validation from the TLS >> protocol is correct, but perhaps this can be explained differently. Perhaps >> the approach should be that TLS depends upon certificate path validation as >> described in RFC 5280. >> >> > In general, TLS's policy (dating back to TLS 1.0) has been that the >> > job of TLS is to carry the certificates and other authentication >> > material but to leave it up to other parts of the system to >> > interpret them. It's been a long time since that decision was made, >> > but from my perspective, there are a number of major reasons: >> > >> > 1. Most of PKI processing (path construction, etc.) is generic and >> > not specific to TLS. What is specific to TLS is: >> > >> > * How to indicate what your PKI capabilities are >> > (see, e.g, S 4.2.4 and 4.3.2) >> > * How to stuff the PKI material into the protocol >> > (principally S 4.4.2) >> > * How to determine whether a given certificate is suitable for >> > use in TLS 4.4.4.2 and 4.3.2.1). >> > >> > So we want to outsource the generic PKI part >> > >> > >> > 2. It matches the software architecture that people often use, >> > which is to have a TLS stack but separate PKI validation. For >> > instance, Firefox uses NSS for TLS but moz::pkix for >> > validation. Similarly, Chrome uses BoringSSL for TLS >> > but the system PKI libraries for validation. >> > >> > >> > In this case, I think that this text was more intended to >> > say "and go read 5280 to learn how to do this". To that end, >> > I suggest we say" >> > >> > >> > "In general detailed certificate validation procedures are out of >> > scope for TLS. [RFC5280] provides general procedures for >> > certificate validation. This section provides TLS-specific >> > requirements.” >> >> I agree with the reasoning, however the dependency on RFC 5280 should be >> called out in a MUST statement. I suggest something like: >> >> "TLS depends on certificate path validation, and a conformant >> TLS implementation MUST implement certificate paths validation >> in a manner that achieves the same result as [RFC5280]. This >> section provides TLS-specific requirements.” >> >> Note that RFC 5280 is already a normative reference. >> >> A MUST here would be a pretty material change to historical TLS practice. >> As Viktor says, there are TLS-using applications that just don't validate >> the cert via 5280 at all. > > I think we want to say that if the certificates are used, then the > certification path MUST be validated in a manner that is compatible with > Internet X.509 certificate profile [RFC5280]; however, other approaches to > validation of the public key, such as the DANE TLSA resource record > [RFC6698], are also acceptable. > > I can see how you would want to say that, but it's not really consistent > either > with historical practice or with the way that other standards track RFCs use > TLS > with certificates (see RFC 5763).
Actually, that is a great example. I accept the need for loose coupling. Russ
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