I disagree that "use" allows multiple uses. Sign/Verify both use the same
algorithm with the same key - just in a producer/consumer role. There would
only be a security problem if the same key was used with *different* algorithms.
For symmetric keys, Sign/Verify operations are actually the same, so in that
case, this is a distinction without a difference.
You may consider the producer/consumer distinction to be multiple uses, but
only in an academic sense. You have to perform both with the same key pair or
symmetric key for the end-to-end cryptography to be meaningful. Doing one
without the other is incomplete. (What good is signing if the signature is
never verified?)
Likewise, Encrypt/Decrypt and Wrap/Unwrap make producer/consumer distinctions,
but also only use a single key with a single algorithm - therefore no security
problem.
====
For what it's worth, I think the different key use representation choices stems
from JOSE being a high-level API that tries to make simple things simple and
WebCrypto being a low-level API that tries to be complete. Both are valid and
useful. These differences show up in lots of places besides just key usage
representations.
Anyway, the purpose of my proposal is to try to make things easier for
WebCrypto. I hope people will get behind it. Yes, having both simple and
detailed key usage representations seems odd at first. But they're designed to
address different goals for different kinds of applications. The alternatives
(such as "signOnly,verifyOnly", etc.) that are currently being considered are
much worse.
-- Mike
-----Original Message-----
From: Ryan Sleevi [mailto:[email protected]]
Sent: Friday, December 27, 2013 2:13 PM
To: John Bradley
Cc: Mike Jones; [email protected]
Subject: Re: [jose] Two proposed JOSE spec actions to more closely coordinate
with WebCrypto
I'm sorry, John, but by your logic, JOSE is not following your own advice.
"enc" is already a multiple-use for a key - it allows for both encryption and
decryption. For that matter, wrap and unwrap, which are supposed to be inferred
based on algorithm, which is a JWE/JWS specific aspect, and not an intrinsic
aspect of JWK-as-key-representation.
Likewise, "sig" implies sign AND verify, which is meant to be unambiguous,
because the assumption is always that you sign with a private key and verify
with a public key, but as a conceptual framework breaks down for schemes like
HMAC, which ostensibly have sign and verify (or MAC and verify, if you prefer,
but we're splitting hairs here).
WebCrypto desires to be *more* precise than JOSE's imprecise and overly broad,
implicitly multi-use syntax. That "enc" means four possible uses, or that "sig"
means two , is a clear sign that JOSE is already actively encouraging multiple
uses for the same key.
Mike's proposal is basically an admission that the ship has sailed on this
implicit, multi-valued usage semantic - which, I can understand and sympathize
with, in the name of backwards compatibility for an in-draft spec, but let's
recognize that as spec'd today, JOSE is preferring and encouraging multiple
uses for the same key in ways that will unquestionably encourage people to make
bad mistakes (such as multiple parties using the same encryption key for
traffic in either direction - requiring some degree of IV sync)
On Tue, December 24, 2013 4:27 pm, John Bradley wrote:
> Having it be an array encourages multiple uses for the same key. I
> have stated many times that encouraging people to do that is not a
> good idea, and making it easy makes people think it is a good idea.
>
> You can use the single value field and have multiple entries with
> different key containing the same or different keys to do the same thing.
>
> On the practical side "use_details" is better than creating crazy dot
> separated como uses.
>
> John B.
>
> On Dec 24, 2013, at 8:26 PM, Mike Jones <[email protected]>
> wrote:
>
> > Hi all,
> >
> > Having reflected upon discussions among WebCrypto and JOSE
> > participants about JWK usage by WebCrypto over the holidays, I'd
> > like to propose the two JOSE spec actions to more closely coordinate with
> > WebCrypto:
> >
> > 1. Change the JWA registry field name from "Implementation
> > Requirements" to "JOSE Implementation Requirements" in the JSON Web
> > Signature and Encryption Algorithms Registry
> > (http://tools.ietf.org/html/draft-ietf-jose-json-web-algorithms-18#section-7.1).
> > This will make it clearer that the Implementation Requirements
> > apply only to JWS and JWE implementations - and not other uses of
> > JWK (such as WebCrypto). This changes only non-normative text and is
> > non-breaking.
> >
> > 2. Define the new JWK field "use_details" for recording intended
> > fine-grained key usage information. This would enable WebCrypto
> > KeyUsage
> > (https://dvcs.w3.org/hg/webcrypto-api/raw-file/tip/spec/Overview.htm
> > l#key-interface) values to be used directly with JWK. The proposed
> > definition is:
> >
> > 3.3. "use_details" (Key Use Details) Parameter
> > The "use_details" (key use details) member identifies fine-grained
> > details the intended use of the key. Its value is an array of
> > key use details values. Values defined by this specification are:
> >
> > o "sign" (compute signature or MAC)
> > o "verify" (verify signature or MAC)
> > o "encrypt" (encrypt content)
> > o "decrypt" (decrypt content and verify decryption, if applicable)
> > o "wrap" (encrypt key)
> > o "unwrap" (decrypt key and verify decryption, if applicable)
> > o "deriveKey" (derive key)
> > o "deriveBits" (derive bits not to be used as a key)
> >
> > Other values MAY be used. Key Use Details values can be registered
> > in the IANA JSON Web Key Use Details registry defined in Section 7.3.
> > The use details values are case-sensitive strings.
> > Duplicate use details values MUST NOT be present in the array.
> > Use of the "use_details" member is OPTIONAL, unless the application
> > requires use this member to record fine-grained key usage details.
> > (Note that the "use_details" values intentionally match the
> > "KeyUsage"
> > values defined in the WebCrypto [WebCrypto] specification.)
> >
> > If both "use" and "use_details" JWK members are present, the usages
> > specified by them MUST be consistent. In particular, the "use" value
> > "sig" corresponds to "sign" and/or "verify". The "use" value
> > "enc" corresponds to all other values defined above.
> > If "use_details" values corresponding to both "sig" and "enc"
> > "use" values are present, the "use" member SHOULD NOT be present,
> > and if present, its value MUST NOT be either "sig" or "enc".
> >
> > This is a non-breaking change - allowing simple applications that
> > want to distinguish between signing and encryption operations to
> > continue doing so as they do today, while also providing a
> > multi-valued key usage details field to be used by applications that
> > want to record fine-grained distinctions among potential key usages,
> > including distinguishing between producer and consumer operations.
> >
> > As I see it, while having two related key usage representations
> > isn't ideal, it's far better than having WebCrypto overload "use"
> > with multi-valued values encoded in strings, such as
> > "signOnly,verifyOnly", which I believe is their current plan of record.
> >
> > Comments?
> >
> > -- Mike
> >
> > P.S. This proposal was already discussed on the WebCrypto list in
> > the thread
> > http://lists.w3.org/Archives/Public/public-webcrypto/2013Dec/0052.ht
> > ml and no objections were raised there that I'm aware of.
> >
> > _______________________________________________
> > jose mailing list
> > [email protected]
> > https://www.ietf.org/mailman/listinfo/jose
>
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