W3C home > Mailing lists > Public > public-webcrypto@w3.org > April 2014

Re: Various comments on the LC draft

From: Ryan Sleevi <sleevi@google.com>
Date: Fri, 25 Apr 2014 18:51:38 -0700
Message-ID: <CACvaWvaMuKkQbFi-65g5ZVNtbWbV8mmi-ma7XVuyHO4AWor9Fw@mail.gmail.com>
To: Mike Jones <Michael.Jones@microsoft.com>
Cc: Vijay Bharadwaj <Vijay.Bharadwaj@microsoft.com>, "public-webcrypto@w3.org" <public-webcrypto@w3.org>
That's great news Mike. I hadn't caught up on the JOSE reviews yet. That at
least resolves how to handle OAEP with the SHA-2 family.


On Fri, Apr 25, 2014 at 6:42 PM, Mike Jones <Michael.Jones@microsoft.com>wrote:

>  FYI, since it’s topical to the OAEP part of this discussion, Kathleen
> Moriarty, the IETF security area director for JOSE, asked us today to add
> the identifier “RSA-OAEP-256”, as described below.  So you could add that
> to the cross-reference table as well.
>
>
>
>                                                                 Cheers,
>
>                                                                 -- Mike
>
>
>
> *From:* Ryan Sleevi [mailto:sleevi@google.com]
> *Sent:* Friday, April 25, 2014 5:25 PM
> *To:* Mike Jones
> *Cc:* Vijay Bharadwaj; public-webcrypto@w3.org
>
> *Subject:* Re: Various comments on the LC draft
>
>
>
>
>
>
>
> On Fri, Apr 25, 2014 at 5:08 PM, Mike Jones <Michael.Jones@microsoft.com>
> wrote:
>
> Thanks for your responses, Ryan.  A few additional comments are included
> below, prefixed by “Mike>”.
>
>
>
> *From:* Ryan Sleevi [mailto:sleevi@google.com]
> *Sent:* Friday, April 25, 2014 3:08 PM
> *To:* Vijay Bharadwaj
> *Cc:* public-webcrypto@w3.org
> *Subject:* Re: Various comments on the LC draft
>
>
>
>
>
>
>
> On Thu, Apr 24, 2014 at 11:42 PM, Vijay Bharadwaj <
> Vijay.Bharadwaj@microsoft.com> wrote:
>
> A few of us at Microsoft read through the LC draft at
> http://www.w3.org/TR/2014/WD-WebCryptoAPI-20140325/ and came up with the
> following comments. They are mostly editorial in nature, so I’m collecting
> them here in one place. I will go through bugzilla and file them over the
> next few days, but do feel free to let me know if any of these is
> controversial. Thanks!
>
>
>
> (The following includes contributions by: Mike Jones, Brian LaMacchia,
> Anthony Nadalin, Israel Hilerio, John Simmons, Kilroy Hughes, and Karen
> Easterbrook.)
>
>
>
> 14.2. Data Types<http://www.w3.org/TR/2014/WD-WebCryptoAPI-20140325/#subtlecrypto-interface-datatypes>
>
> This says “jwk” “The key is represented as JSON according to the JSON Web
> Key format.”  This will need to be reworded as part of Bug 24963<https://www.w3.org/Bugs/Public/show_bug.cgi?id=24963>to clarify the type of the returned object (whether ArrayBuffer or JWK).
>
>
>
> Agreed
>
>
>
>
>
> 14.3. Methods and Parameters<http://www.w3.org/TR/2014/WD-WebCryptoAPI-20140325/#subtlecrypto-interface-methods>
>
> In 14.3.1 through 14.3.12, we have statements like “If the name<http://www.w3.org/TR/2014/WD-WebCryptoAPI-20140325/#dfn-Algorithm-name>member of
> normalizedAlgorithm does not identify a registered algorithm<http://www.w3.org/TR/2014/WD-WebCryptoAPI-20140325/#algorithms>that supports the encrypt operation, then return
> an error<http://www.w3.org/TR/2014/WD-WebCryptoAPI-20140325/#concept-return-an-error>named
> NotSupportedError<http://www.w3.org/TR/2014/WD-WebCryptoAPI-20140325/#dfn-NotSupportedError>”.
> It seems possible that limited devices (such as embedded devices or
> implementations using hardware crypto modules) will not support the entire
> range of parameters or operations. Even with software implementations, not
> all parameter values will be supported – for example every RSA
> implementation in practice only supports a fixed set of key sizes.
> Therefore we believe these statements should be augmented in each
> occurrence to say something like: “If the name<http://www.w3.org/TR/2014/WD-WebCryptoAPI-20140325/#dfn-Algorithm-name>member of
> normalizedAlgorithm does not identify a registered algorithm<http://www.w3.org/TR/2014/WD-WebCryptoAPI-20140325/#algorithms>that supports the encrypt operation, or if the implementation does not
> support the encrypt operation with this algorithm using the specified
> parameters, then return an error<http://www.w3.org/TR/2014/WD-WebCryptoAPI-20140325/#concept-return-an-error>named
> NotSupportedError<http://www.w3.org/TR/2014/WD-WebCryptoAPI-20140325/#dfn-NotSupportedError>
> ”.
>
>
>
>
>
> I'm not a fan of this change as proposed, though I am supportive of the
> reasoning.
>
>
>
> A couple issues with it:
>
> 1) For implementation consistency, the check about whether nor not the
> specified parameters are valid needs to be deferred to the per-algorithm
> sections (eg: 18.4.5), since that's where they are normalized into the
> parameter type specific for the algorithm.
>
> 2) Implementations - including software implementations - may not fully be
> aware of what is supported or not. For example, a given algorithm may be
> known by the UA, and be known by the cryptographic library or
> implementation that the UA uses, but be disabled through means that the UA
> doesn't know about (eg: a group policy to disable a legacy algorithm). From
> a UA/implementer perspective, it's simply "the operation failed"
>
>
>
> Support for "operation failed" consistently across all operations was
> something Eric Roman already raised as
> https://www.w3.org/Bugs/Public/show_bug.cgi?id=25422 and
> https://www.w3.org/Bugs/Public/show_bug.cgi?id=25420
>
>
>
> As such, I think the current wording - which allows "performing the
> operation results in an error" to raise an OperationError - provides the
> ability for implementations that don't support all parameters to return an
> error.
>
>
>
> As an implementor, I don't think we can reasonably distinguish between all
> the possible NotSupportedErrors, and thus I would prefer that the spec not
> mandate that specific error.
>
>
>
> Mike> The gist of this one is that the wording currently makes it seem
> like you can only return “NotSupportedError” in a particular case, whereas
> there are lots of other cases in which implementations might reasonably
> return it.  The spec should be worded to allow this.
>
>
>
>  18.2. Recommended algorithms<http://www.w3.org/TR/2014/WD-WebCryptoAPI-20140325/#recommended-algorithms>
>
> Please add these algorithms:
>
> ·         RSASSA-PKCS1-v1_5 using SHA-256 (This is in the Recommended set
> for JOSE, and more secure than the SHA-1 variant in the spec.)
>
> ·         RSA-OAEP using SHA-1 and MGF1 with SHA-1 (This is the RFC 3447
> default and the mostly widely deployed OAEP variant. It is also the variant
> used by JOSE)
>
>
>
> I'm fairly certain this section is going to continue to cause nothing but
> trouble, for both reviewers (as in the CFRG WG) and for implementors.
>
>
>
> I know we (as a WG) continue to waffle on this, but I can't help but feel
> it's better off removed entirely.
>
>
>
> Mike> Unless it’s removed entirely, can you please add these, as they are
> what JOSE implementations use?
>
>
>
> 18.8.7. ECDSA Operations<http://www.w3.org/TR/2014/WD-WebCryptoAPI-20140325/#ecdsa-operations>
>
> Section 18.8.4 specifies the valid values of NamedCurve, but
> curve-specific instructions are scattered through the Import Key and Export
> Key sections of Section 18.8.7. It seems better to collect curve-specific
> items in a table in Section 18.8.4, listing the DOMString value, the curve
> specification and the curve OID, and then to make the text describing the
> operations generic. This would allow for easy extensibility of the spec in
> the future and make the current version easier to read. For example, step
> 11 in the SPKI subsection of Import Key in Section 18.8.7 could say, “If
> params is equivalent to one of the object identifiers listed in Section
> 18.8.4, set the namedCurve attribute of algorithm to the corresponding
> DOMString value.” Similar problems exist in 18.9.4. ECDH Operations<http://www.w3.org/TR/2014/WD-WebCryptoAPI-20140325/#ecdh-operations>
> .
>
>
>
> So I understand the motivation for this, but at the same time, the EC
> cases follow the same pattern as the other algorithms - which may have more
> complexity (eg: the PSS and OAEP cases).
>
>
>
> We've discussed normative tables before, but that is not really followed
> by any other web specifications. The tables are provided for informative
> reference, but the normative algorithms are explicitly stated.
>
>
>
> Mike> The real problem is that, as written, the “Otherwise” clause of
> Import Key operation requires that an error be returned if the curve is not
> one of secp256r1, secp384r1, or secp521r1.  This MUST be generalized to
> allow implementations to support other curves, even if those curves aren’t
> specified in the initial version of this specification.  This problem must
> also be corrected in other locations where it occurs, such as 18.9.4.
> ECDH Operations<http://www.w3.org/TR/2014/WD-WebCryptoAPI-20140325/#ecdh-operations>
> .
>
>
>
> This is no different than the change (back) to enums that we've received
> feedback on (from TAG and ex-TAG).
>
>
>
> When an implementation wants to support other curves, they'll propose
> edits. The same way implementations do for every other web feature they
> support or add experimental support for.
>
>
>
> I do not support making this change.
>
>
>
>
>
>
>
> 18.9.4. ECDH Operations<http://www.w3.org/TR/2014/WD-WebCryptoAPI-20140325/#ecdh-operations>
>
> As I’ve mentioned before, SP800-56A Section 5.7 prohibits exposing the DH
> / ECDH shared secret directly and instead requires that it be run through a
> KDF before being used. Many FIPS-validated implementations follow this
> restriction. Allowing the Derive Bits operation with DH or ECDH violates
> this prohibition.  We should recognize that at least some implementations
> will only expose deriveKey and not deriveBits with these algorithms, and
> make the latter optional.
>
>
>
> I don't think we can get consensus here. I understand your point, but at
> the same time, Microsoft's own APIs do not follow this limitation,
> precisely because it's recognized as a valid use case.
>
>
>
> Given how much considerable 'optionality' is already present in the spec,
> I cannot feel we'd be doing even more harm to developers to suggest
> yet-another-inconsistent-between-browsers feature. If anything, it gets
> removed entirely, which would be extremely unfortunate for the valid use
> cases discussed previously.
>
>
>
>
>
> 20.1. Generate a signing key pair, sign some data<http://www.w3.org/TR/2014/WD-WebCryptoAPI-20140325/#examples-signing>
>
> Delete the comma from this example text:
>
> hash: {
>
>     name: "SHA-256",
>
>   }
>
>
>
>
>
> Agreed
>
>
>
>  21.1. JSON Web Signature and Encryption Algorithms Registration<http://www.w3.org/TR/2014/WD-WebCryptoAPI-20140325/#iana-section-jws-jwa>
>
> The “HS1” algorithm could legally be used in a JWS object.  Therefore,
> change the “HS1” registration to read:
>
>    - Algorithm Name: "HS1"
>    - Algorithm Description: HMAC using SHA-1
>    - Algorithm Usage Location(s): "alg"
>    - JOSE Implementation Requirements: Deprecated
>    - Change Controller: W3C Web Cryptography Working Group
>    - Specification Document(s): [[ This Document ]]
>
>
>
> The document failed to register the “RS1” algorithm identifier, which
> could legally be used in a JWS object.  Therefore, please add this
> registration:
>
>    - Algorithm Name: "RS1"
>    - Algorithm Description: RSASSA-PKCS-v1_5 using SHA-1
>    - Algorithm Usage Location(s): "alg"
>    - JOSE Implementation Requirements: Deprecated
>    - Change Controller: W3C Web Cryptography Working Group
>    - Specification Document(s): [[ This Document ]]
>
>
>
>
>
> I strongly oppose both of these. If you want to add algorithms usable for
> JOSE, discuss with the JOSE WG. We shouldn't be using Web Crypto to
> circumvent their process. That the registry exists and allows for non-JOSE
> algorithms is great, but we should at least respect the domain of JOSE, who
> has made specific security choices on this.
>
>
>
> Mike> JOSE defined those registries **exactly** so that third parties
> could define algorithms usable in JOSE implementations.  That **is** a
> process defined by JOSE.  Adding these wouldn’t be circumventing the
> process – it would be using it.
>
>
>
> Also, the WebCrypto document should be consistent.  You’re defining the
> “RS1” alg value, therefore you need to register it, like you’re already
> doing for “HS1”.
>
>
>
> I agree, we need to register. However, I cannot support adding algorithms
> like "RS1" or "HS1" to be supported by JWS. We are not a WG equipped to
> comment on JWS modifications. Leave that for JOSE.
>
>
>
> If you feel that these should be valid algorithms for JWS, I would
> encourage you to take it to the JOSE WG for discussion. We don't *use* JWS
> in our spec, it's entirely inappropriate to suggest an algorithm would be
> appropriate to use for it.
>
>
>
> As editor of JWS, I'm sure you'll find it very easy to add :)
>
>
>
>      21.2. JSON Web Key Parameters Registry<http://www.w3.org/TR/2014/WD-WebCryptoAPI-20140325/#iana-section-jwk>
>
> Change word “Registry” to “Registration” in section title.
>
>
>
> The registration is missing the required “Parameter Description” clause.
> Please add this clause to the registration of “ext”:
>
>    - Parameter Description: Extractable
>
>
>
>  Agreed
>
>
>
>  23.1. Normative References<http://www.w3.org/TR/2014/WD-WebCryptoAPI-20140325/#normative-references>
>
> There are references throughout the spec to “ECMA262” and yet the
> reference in the References section is labelled “ECMAScript”.  These names
> should be made consistent.
>
>
>
> A.1. Algorithm mappings<http://www.w3.org/TR/2014/WD-WebCryptoAPI-20140325/#jwk-mapping-alg>
>
> Add the curve names to the “EC” mappings.  For instance, this:
>
> { kty: "EC",
>
>   alg: "ES256" }
>
> should become this:
>
> { kty: "EC",
>
>   crv: "P-256",
>
>   alg: "ES256" }
>
> (and do the same for P-384 and P-521).
>
>
>
> This was not an accidental omission. The absence of parameters for other
> cases - such as RSA - was equally intentional. "crv" is a property of the
> key itself (much like "n" or "e").
>
>
>
> Mike> I disagree – “crv” is a property of the algorithm.  I don’t feel
> super-strong about this one, but it would seem more helpful to implementers
> to include the “crv” parameter in the table than to omit it.  It’s
> non-normative, so it’s not like including it would confuse anyone, and it
> would help some.
>
>
>
> That's not what JWA says - so your disagreement is with a spec you're
> editing :)
>
>
>
> That is, "crv" is in the section of "Parameters for Elliptic Curve Public
> Keys" (in JWA), whereas that table tries to limit itself to those items
> listed under "JSON Web Key (JWK) Format" (in JWK) - which lists "kty" and
> "alg".
>
>
>
>
>
> JWA makes it clear what the crv should be if the "alg" is present, which
> is what that mapping describes (informatively).
>
>
>
> Now, it might be argued that there is a case to be made so that
>
> { kty: "EC", crv: "P-256" }
>
>
>
> is recognized as { name: "ECDSA", namedCurve: "P-256", hash: { name:
> "SHA-256" } }, but that would be a change to 18.8.7
>
>
>
> I've filed https://www.w3.org/Bugs/Public/show_bug.cgi?id=25465 to
> clarify this, and https://www.w3.org/Bugs/Public/show_bug.cgi?id=25466for related.
>
>
>
>
>
> Add this new mapping entry:
>
> { kty: "RSA",
>
>   alg: "RSA-OAEP" }
>
> to:
>
> { name: "RSA-OAEP",
>
>   hash: {name: "SHA-1"}
>
> }
>
>
>
>
>
> Yes, although we'll need to be careful to track JOSE. As has been noted in
> the JOSE group, the choice of OAEP with SHA-1 is "unfortunate" - and
> inconsistent with how JOSE has treated other parameterized algorithms.
>
>
>
> Mike> The choice isn’t unfortunate – it’s deliberate, because that’s
> what’s actually deployed.  This was extensively discussed in JOSE and most
> participants believed that using the default parameters was the right call
> – especially since many implementations don’t provide any way to change to
> using a different hash function.
>
>
>
> Let me rephrase this
>
>
>
> The choice of naming it "RSA-OAEP" is unfortunate, and breaks tradition
> with all of your other algorithms.
>
>
>
> If you were to talk about consistent naming, this would be something like
> "ROS1" (comparable to "PS256" or "RS256".
>
>
>
> That you've chosen "RSA-OAEP" as a name means that every other user of
> OAEP - including when libraries do (inevitably) offer the ability to use
> OAEP with SHA-256/mgf1-sha256 - will have to find some other name.
>
>
>
> That's why the editors note is there - there is no guidance or pattern
> from JOSE on how, if WebCrypto wanted (and can) support OAEP with other
> algorithms, it would expose that as the "alg" name. "RSA-OAEP-256"?
>
>
>
> In the same way we've chosen to add other algorithms to the table, we, as
> a WG, need to decide how to handle JOSE's choice to omit other, valid OAEP
> forms - and how to express them for JWK export. Right now, it's unspecified.
>
>
>
>      Add this new mapping entry:
>
> { kty: "RSA",
>
>   alg: "RS1" }
>
> to:
>
> { name: " RSASSA-PKCS1-v1_5",
>
>   hash: {name: "SHA-1"}
>
> }
>
>
>
> We would not suggest adding entries for RSA-PSS with SHA-1, ECDSA with
> SHA-1 or ECDSA where the curve is not aligned with the hash.
>
>
>
>
>
> Any reasoning behind that? Having RSA-OAEP use SHA-1/mgf1-with-SHA1 but
> not having RSA-PSS do the same seems somewhat inconsistent, given the
> rationale JOSE as put forth.
>
>
>
> Mike> In the implementation survey conducted in 2012, there was already
> widespread support for RSASSA-PKCS1-v1_5 with SHA-256, so there was no
> problem specifying it for JWS.  However, there was not widespread support
> for OAEP with SHA-256, so that wasn’t specified.  I personally agree with
> you that we needn’t have specified any PSS identifiers at all, since it’s
> also not widely deployed, but given that it wasn’t, we weren’t breaking
> anything by specifying PSS with SHA-2, since mostly it isn’t deployed at
> all in any form.
>
>
>
>                                                                 -- Mike
>
>
>
>
>
> That's great - for JOSE. That still doesn't solve the issue for this WG,
> which describes an API that allows supporting PSS with SHA-1 or OAEP with
> SHA-256. If/when an implementation supports them (and there are some that
> can), we still have to figure out what the relevant JWA alg entries should
> be, independent of JOSE.
>
>
>
Received on Saturday, 26 April 2014 01:52:07 UTC

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