> On May 15, 2017, at 7:01 PM, Eric Rescorla <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. Russ
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