Re: [jose] TTL for JWK

Mike Jones <> Wed, 20 February 2013 03:32 UTC

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From: Mike Jones <>
To: John Bradley <>, Brian Campbell <>
Thread-Topic: [jose] TTL for JWK
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Date: Wed, 20 Feb 2013 03:31:44 +0000
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Subject: Re: [jose] TTL for JWK
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So sort of "may cache until"?

I don't think TTL is the right term for this. When am IP packet's ttl value reaches 0, the packet is discarded.

-- Mike

From: John Bradley
Sent: 2/19/2013 7:14 PM
To: Brian Campbell
Cc: Mike Jones;
Subject: Re: [jose] TTL for JWK

Yes ttl and exp are different.    ttl probably should apply to a JWK set as a whole rather than the individual JWK where exp is certainly a per key value.

Mike, this is a bit like the distinction in DNS.

John B.

On 2013-02-19, at 9:26 PM, Brian Campbell <<>> wrote:

The subtle (and maybe unimportant) distinction I was trying to make was that this was more of a indicator about how long a key could be cached/used with a reasonable expectation that things would still work. I tend to think of key expiration as being something more like any use of the key after the time should be considered invalid. I wanted to avoid requiring message rejection if expiration checks failed (as is the case with exp in JWT).  I remember the change to RSA to free up "exp" and was going to propose just using that. But after thinking about it a bit, to me anyway, "ttl" conveyed that idea better than "exp." I'd be fine with either parameter name though.

Does that make sense?

On Tue, Feb 19, 2013 at 5:04 PM, Mike Jones <<>> wrote:
Is this a key expiration time parameter or is there a subtle distinction that I’m missing?  If it is an expiration time, I’d recommend that if we do this, that we reuse the name “exp” from the JWT spec.  (We actually stopped using this name as an RSA parameter name a few drafts ago exactly so we could use it for this purpose.)

                                                            -- Mike

From:<> [<>] On Behalf Of Brian Campbell
Sent: Tuesday, February 19, 2013 3:43 PM
Subject: [jose] TTL for JWK

I'd like to float the idea of introducing a time to live parameter to the base JWK document, which could probably fit in as a subsection of §4 that defines parameters common to all key types [1].

The motivation is that many uses of JWKs will involve caching of JWK data and a TTL parameter could be used to indicate how long a key could be safely cached and used without needing to recheck the JWK source. I don't want it to be a hard expiration date for the key but rather a hint to help facility efficient and error free caching.

OpenID Connect has a real use case for this where entities publish their keys via a JWK Set at an HTTPS URL. To support key rotation and encryption, there needs to be some way to indicate the TTL of a public key used to encrypt. Of course, this isn't the only way to skin that cat but it strikes me as a good way and one that might provide utility for JWK in other contexts.
JSON Web Token [2] defines a data type that is "A JSON numeric value representing the number of seconds from 1970-01-01T0:0:0Z UTC until the specified UTC date/time" that seems like it could be co-opted to work well as the value for a "ttl" parameter.



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