First we should agree on a common understanding of the spec. The reason why age works with unsynchronized clocks is that the client determines issue_date based on the time when it receives the token over the wire. This depends on the server and client both recording time this way and for the transmission of the token to be be not longer than the margin of error for validating age. Are we agreed on this understanding?
The easiest case for me to explain here is client credentials because I have to assume you've built and registered a Twitter app at some point (or similar OAuth 1.0a app). You registered your app on the site and were issued a client_id and client_secret (called consumer_key and consumer_secret in 1.0). You then embedded these values in your client (they were not issued programmatically to your app). Assuming the MAC token algorithm is used then for establishing client identity (originally one of the uses we, the working group, hoped MAC would cover) how then will your client determine issue date? After we can establish where you're at on the two above points I'll continue with the explanation. But as a preview, the next points would be: - If issue_date comes form the server, how is it translated to the client? - If you use a server provided issue_date, how do you then translate that a value relative to the local unsyncronized clock? - If your answer to that is to also provide the current server time to the client so the offset on the server provided issue_date can be calculated what is the difference between all of these values and just using timestamp? So don't get wrapped up in those 3 questions until we establish your contextual understanding of the first two paragraphs. Feel free to also respond to me off the list so we don't trouble everyone else with us getting on the same page (the reason, I thought, why a Skype call would be more efficient and painless). I do think my explainations all have been very clear thus far. There must be a contextual confusion that is keeping us from a common understanding of the terminology or the use cases. skylar On May 31, 2011, at 10:30 AM, Adam Barth wrote: > I'm not sure we need a Skype call. Can you explain the trouble caused > by age clearly? I didn't understand your previous explanation. The > more concrete you can be, the better. > > Thanks, > Adam > > > On Tue, May 31, 2011 at 1:04 AM, Skylar Woodward <sky...@kiva.org> wrote: >> It seems we're failing to communicate. Or you're not understanding my use >> cases. Age doesn't "just" work. It only works for a limited number of uses >> cases that must include all of yours - and it is brittle at that. It doesn't >> work for any of our uses cases (where the client can't know issue_date w/o >> the server telling it - in which case we have the equivalent problem as >> timestamp). >> >> If you'd like to talk this out over Skype I'm happy to do that, so I can >> help you understand why age doesn't work. >> >> >> >> On May 31, 2011, at 9:47 AM, Adam Barth wrote: >> >>> Timestamps don't work when the client doesn't have a synchronized >>> clock. It's true that a client could synchronize its clock with the >>> network, but our implementation experience is that many clients don't >>> for a variety of reasons. That means that age better because, you >>> know, it works. >>> >>> Adam >>> >>> >>> On Mon, May 30, 2011 at 11:19 PM, Skylar Woodward <sky...@kiva.org> wrote: >>>> I don't think you read my first message on the topic (or I wrote too much). >>>> >>>> Age is fragile because if the clock changes between issue_date and the >>>> time of submission, it will fail. We know many people don't have >>>> synchronized clocks, but using age only solves this problem if two >>>> assumptions hold true: >>>> >>>> 1) the client is able to guess the issue_date the server is using based on >>>> the time the credential was issued >>>> 2) the client system clock doesn't change between issue date and >>>> submission time. >>>> >>>> Timestamp has neither of these issues because the client can always >>>> inquire about network time and can effectively correct for inaccuracies in >>>> the device timekeeping system. >>>> >>>> Regarding the first assumption, this fails when a token might be re-issued >>>> between devices. An example is that we use MAC token for the client >>>> credentials, which are issued when a developer registers an application. >>>> The client has no way of determining on its own when the value was >>>> actually issued (unless we communicate that on the developer website and >>>> force users to embed that with client_id, which adds usability issues of >>>> users copying and entering string date values correctly). The same is >>>> actually true for all of our OAuth access tokens because we reissue tokens >>>> to the same client_id if they were previously issued and are still valid. >>>> (The client would thus think the issue_date was now() when if fact it was >>>> the time of the first issue for client_id+scope+grantor_id). Thus, age is >>>> really just a convoluted way of trying to communicate the device system >>>> offset: >>>> >>>> local_offset = current_server_time - current_device_time >>>> age = current_device_time - (server_issue_date-local_offset) >>>> >>>> Since the protocol doesn't currently allow for server_issue_date to be >>>> given with tokens, thus age currently can't have the resilience that >>>> timestamp does. It also forces servers to issue new tokens on demand just >>>> to make the convoluted age system work (rather than reuse existing valid >>>> tokens). Or, you have to modify the protocol to add server_issue_date and >>>> current_server_time into the token-issue exchange - eg, more complexity. >>>> >>>> Timestamp is simpler, proven, it and it has a solution for your use case >>>> of unsyncronized clocks. >>>> >>>> skylar >>>> >>>> >>>> On May 30, 2011, at 9:08 AM, Adam Barth wrote: >>>> >>>>> I can't speak for Mozilla, but I can tell you that many folks don't >>>>> have synchronized clocks, for a wide variety of reasons. I guess I >>>>> don't really understand why you view age as problematic. You >>>>> reference "fragility of using time-since-credentials-issued" but you >>>>> don't say what exactly is fragile about it. There's nothing >>>>> particularly complex about age, especially when using the monotonic >>>>> clock provided by all modern operating systems. >>>>> >>>>> Adam >>>>> >>>>> >>>>> On Mon, May 30, 2011 at 12:03 AM, Skylar Woodward <sky...@kiva.org> wrote: >>>>>> But see, now you are specializing the use of MAC token even more - now >>>>>> it's becoming a service mainly for user-agents on home desktops? This is >>>>>> further for the original goal of making MAC as flexible is possible. In >>>>>> this case you should change the spec name to >>>>>> MAC_TOKEN_FOR_BROWSER_COOKIE_REPLACEMENT_IN_AGENTS_LIKE_FIREFOX - or >>>>>> MTBCRLF for short. >>>>>> >>>>>> Sarcasm aside, my point is that timestamp is just as good as your offset >>>>>> technique and is more: reliable, straightforward, flexible. >>>>>> >>>>>> User agents that care about creating robust behavior for home desktops >>>>>> or mobiles (presumably of users and OS not yet sophisticated enough to >>>>>> check network time on their own) should be advised to do clock >>>>>> correction on their own (by pinging a time service) and trusting the >>>>>> device clock alone. >>>>>> >>>>>> Please change the spec back to using timestamp rather than age. >>>>>> >>>>>> I'd also like to hear a convincing argument from the Mozilla co-authors >>>>>> about why they think that age is more resilient than the above (I >>>>>> believe it is not) and further more why they would find the above >>>>>> unattractive or difficult to implement in a modern user-agent. >>>>>> >>>>>> Thanks, >>>>>> skylar >>>>>> >>>>>> ... -.- -.-- .-.. .- .-. — .-- --- --- -.. .-- .- .-. -.. — ... -.- -.-- >>>>>> .-.. .- .-. — .-- --- --- -.. .-- .- .-. -.. >>>>>> skylar woodward >>>>>> Kiva Developer Program / build.kiva.org / @buildkiva >>>>>> >>>>>> >>>>>> On May 30, 2011, at 7:54 AM, Eran Hammer-Lahav wrote: >>>>>> >>>>>>> Any kind of clock sync requirement for user-agents (basically, home >>>>>>> desktops) it completely impractical. The added complexity pales in >>>>>>> comparison to the difficulty of trying to use timestamps and any kind >>>>>>> of clock sync. No window will be big enough as experience shows some >>>>>>> users have closes that are off by more than an hour and a half. >>>>>>> >>>>>>> The issue here is who is this being optimized for. Server-to-server >>>>>>> communication should simply use TLS for privacy and MITM protection on >>>>>>> top of MAC instead of using nonces to prevent replay. The whole point >>>>>>> of this kind of replay protection is when TLS is not available. >>>>>>> >>>>>>> I think a better approach is to simply make checking the nonce optional >>>>>>> when TLS is used. >>>>>>> >>>>>>> EHL >>>>>>> >>>>>>>> -----Original Message----- >>>>>>>> From: oauth-boun...@ietf.org [mailto:oauth-boun...@ietf.org] On Behalf >>>>>>>> Of Peter Wolanin >>>>>>>> Sent: Sunday, May 29, 2011 6:53 PM >>>>>>>> To: Skylar Woodward >>>>>>>> Cc: OAuth WG >>>>>>>> Subject: Re: [OAUTH-WG] Fwd: issues with token age element - MAC token >>>>>>>> >>>>>>>> I am also concerned by the fragility of using >>>>>>>> time-since-credentials-issued, >>>>>>>> and also the added complexity of specifying this construction. >>>>>>>> >>>>>>>> I think it would be preferable to always require a timestamp as part >>>>>>>> of the >>>>>>>> authorization header, and maybe even include in the spec a maximum time >>>>>>>> difference between client and server (e.g. 900 seconds) that can be >>>>>>>> tolerated. This makes generating the nonce easier also, since the >>>>>>>> value need >>>>>>>> to longer be unique over all time. >>>>>>>> >>>>>>>> We have such rules in place for an HMAC-based authentication system we >>>>>>>> use. Once in a while a client has a local clock so far out of sync >>>>>>>> that there is an >>>>>>>> issue, but it's rare. >>>>>>>> >>>>>>>> -Peter >>>>>>>> >>>>>>>> On Mon, May 23, 2011 at 9:16 PM, Skylar Woodward <sky...@kiva.org> >>>>>>>> wrote: >>>>>>>>> Resending to the list from my subscribed account... >>>>>>>>> >>>>>>>>> Begin forwarded message: >>>>>>>>> >>>>>>>>>> From: Skylar Woodward <sky...@larw.com> >>>>>>>>>> Date: May 23, 2011 6:14:00 PM PDT >>>>>>>>>> To: Skylar Woodward <sky...@kiva.org> >>>>>>>>>> Cc: Eran Hammer-Lahav <e...@hueniverse.com>, OAuth WG >>>>>>>>>> <oauth@ietf.org> >>>>>>>>>> Subject: Re: [OAUTH-WG] issues with token age element - MAC token >>>>>>>>>> >>>>>>>>>> So after discussing this today and reflecting on it a bit, I would >>>>>>>>>> suggest that >>>>>>>> nonce simply be the "unique value" (as it is so named) without further >>>>>>>> requirements. It might be suggested that this be composed of an >>>>>>>> random+timestamp (not age) value, but that seems more of a MAY or >>>>>>>> "recommended" practice. If the expectation is that very few if any >>>>>>>> providers >>>>>>>> would actually check the timestamp (or moreover, the nonce itself), >>>>>>>> why add >>>>>>>> terminology in the draft that requires it? Developers are doing extra >>>>>>>> housekeeping (and perhaps for a perceived benefit) but with no payoff >>>>>>>> or >>>>>>>> added security. >>>>>>>>>> >>>>>>>>>> I'm sending this feedback based on having implemented the v3-5 >>>>>>>>>> changes >>>>>>>> last night (for both client credentials and requests w/ access >>>>>>>> tokens). After >>>>>>>> the changes, the nonce creation is now the most complicated part of the >>>>>>>> normalized request string and yet these changes offer the least >>>>>>>> benefit. >>>>>>>> What's most important is that nonces are unique on each request for an >>>>>>>> ID. >>>>>>>>>> >>>>>>>>>> There are issues with age as well: >>>>>>>>>> >>>>>>>>>> - As Bill mentioned, if the client stores the issue time based on >>>>>>>>>> receipt, then the internal clock changes (presumably w/o knowledge of >>>>>>>>>> the software storing the dates) then time will also fail. Assuming >>>>>>>>>> that a user with a bad clock (of by hours or more) will never fix it >>>>>>>>>> and actually encourages bad user behavior (don't fix your clock or >>>>>>>>>> Twitterbot will stop working!). Though we say that timezones won't >>>>>>>>>> bring about the situation of changed clock, I'd be to differ. Many >>>>>>>>>> users aren't savvy enough to change time zone, but just adjust the >>>>>>>>>> time to local time anyway. Users who are more likely to get it right >>>>>>>>>> already have auto clock sync enabled (via web, mobile, etc.) >>>>>>>>>> >>>>>>>>>> - What if the token wasn't originally issued programmatically? In >>>>>>>>>> this case, >>>>>>>> the issue time has to be obtained from the server and stored on the >>>>>>>> client >>>>>>>> then you have the same problem as with a timestamp - the client clock >>>>>>>> is not >>>>>>>> sync'd to the server clock and there is no adjustment. You want this >>>>>>>> to apply >>>>>>>> to uses outside of just OAuth, but now requiring the client to be able >>>>>>>> to >>>>>>>> determine an issue time based on when it receives an HTTP request >>>>>>>> necessarily limits the types of token flows for which this can be used. >>>>>>>>>> >>>>>>>>>> - It's one more detail to store. Hardly an issue for a developer, >>>>>>>>>> but it is >>>>>>>> inelegant. It's like having a double ID. Yet it's not an ID, it is >>>>>>>> actually more of a >>>>>>>> recording of "my personal clock offset value" but obfuscated several >>>>>>>> times >>>>>>>> over (one for each token) as issue_date. >>>>>>>>>> >>>>>>>>>> - This implementation assumes software programs use the computer >>>>>>>> internal clock exclusively for timestamp. A robust program that is >>>>>>>> dependent >>>>>>>> on accurate timestamps would ping the origin server (or similar >>>>>>>> trusted time >>>>>>>> authority) to ask it the current time. Then it could store a "my >>>>>>>> device clock >>>>>>>> offset" value for the lifetime of the program execution. All requests >>>>>>>> needing >>>>>>>> timestamp would be adjusted accordingly. For age, if the clock is >>>>>>>> changed >>>>>>>> since the stored issue_date, the problem can't be corrected in this >>>>>>>> manner. >>>>>>>> Thus, a significant advantage for timestamp. >>>>>>>>>> >>>>>>>>>> All in all, this seems like a misguided but well-intentioned attempt >>>>>>>>>> to get >>>>>>>> around end-user issues of mis-set clocks. It feels like a hack and it >>>>>>>> certainly >>>>>>>> isn't a foolproof solution. The more I think about the implications of >>>>>>>> the age >>>>>>>> parameter, the less I like it. Timestamp has been used for many years >>>>>>>> in the >>>>>>>> industry and with reasonable success in relevant applications. If we >>>>>>>> change to >>>>>>>> a new way of trying to sync on time I think we run a greater risk of >>>>>>>> stumbling >>>>>>>> upon unforeseen issues, such as those outlined above. >>>>>>>>>> >>>>>>>>>> I recommend the requirement of an age (or timestamp for that matter) >>>>>>>> be dropped from the nonce construction. For providers that deem it >>>>>>>> valuable, timestamp can be an optional value (either as part of the >>>>>>>> nonce or >>>>>>>> the overall header, as before). >>>>>>>>>> >>>>>>>>>> skylar >>>>>>>>>> >>>>>>>>>> >>>>>>>>>> >>>>>>>>>> On May 23, 2011, at 2:11 AM, Skylar Woodward wrote: >>>>>>>>>> >>>>>>>>>>> You may have noticed, on page 8 the host is listed as "example.net" >>>>>>>>>>> - should be example.com, I believe. (draft v5) >>>>>>>>>>> >>>>>>>>>>> All in all, I'm in support of the changes in v2. Certainly >>>>>>>>>>> addresses my >>>>>>>> hesitations from v2. >>>>>>>>>>> >>>>>>>>>>> skylar >>>>>>>>>>> >>>>>>>>>>> >>>>>>>>>>> On May 9, 2011, at 12:36 PM, Eran Hammer-Lahav wrote: >>>>>>>>>>> >>>>>>>>>>>> (Please discuss this draft on the Apps-Discuss >>>>>>>>>>>> <apps-disc...@ietf.org> mailing list) >>>>>>>>>>>> >>>>>>>>>>>> http://tools.ietf.org/html/draft-hammer-oauth-v2-mac-token >>>>>>>>>>>> >>>>>>>>>>>> While this document has moved to the Apps-Discuss mailing list for >>>>>>>>>>>> the >>>>>>>> time being, I wanted to give a quick update to those who have been >>>>>>>> following this draft which originated on this list. >>>>>>>>>>>> >>>>>>>>>>>> The major changes since -02 are: >>>>>>>>>>>> >>>>>>>>>>>> * Removed OAuth terminology and association. The draft is now a >>>>>>>> general purpose HTTP authentication scheme. It does include an OAuth >>>>>>>> 2.0 >>>>>>>> binding which is described in less than a page. One suggestion would >>>>>>>> be to >>>>>>>> move section 5.1 into the OAuth specification and drop all the OAuth >>>>>>>> 2.0 text >>>>>>>> from the MAC draft. >>>>>>>>>>>> >>>>>>>>>>>> * Added 'Set-Cookie' extension for using MAC with session cookies. >>>>>>>>>>>> >>>>>>>>>>>> * Removed request URI query normalization. The new draft uses the >>>>>>>> raw request URI unchanged. >>>>>>>>>>>> >>>>>>>>>>>> * Replaced timestamps with credentials age to remove the need for >>>>>>>> clock sync. >>>>>>>>>>>> >>>>>>>>>>>> * Added a placeholder for extension, allowing random text to be >>>>>>>> included in the request and MAC. >>>>>>>>>>>> >>>>>>>>>>>> * Added issuer attribute for identifying the source of the >>>>>>>>>>>> credentials as >>>>>>>> an additional protection. >>>>>>>>>>>> >>>>>>>>>>>> Draft -04 is not compatible with previous drafts. >>>>>>>>>>>> >>>>>>>>>>>> EHL >>>>>>>>>>>> _______________________________________________ >>>>>>>>>>>> OAuth mailing list >>>>>>>>>>>> OAuth@ietf.org >>>>>>>>>>>> https://www.ietf.org/mailman/listinfo/oauth >>>>>>>>>>> >>>>>>>>>> >>>>>>>>> >>>>>>>>> _______________________________________________ >>>>>>>>> OAuth mailing list >>>>>>>>> OAuth@ietf.org >>>>>>>>> https://www.ietf.org/mailman/listinfo/oauth >>>>>>>>> >>>>>>>> >>>>>>>> >>>>>>>> >>>>>>>> -- >>>>>>>> Peter M. Wolanin, Ph.D. : Momentum Specialist, Acquia. Inc. >>>>>>>> peter.wola...@acquia.com : 978-296-5247 >>>>>>>> >>>>>>>> "Get a free, hosted Drupal 7 site: http://www.drupalgardens.com"; >>>>>>>> _______________________________________________ >>>>>>>> OAuth mailing list >>>>>>>> OAuth@ietf.org >>>>>>>> https://www.ietf.org/mailman/listinfo/oauth >>>>>> >>>>>> _______________________________________________ >>>>>> OAuth mailing list >>>>>> OAuth@ietf.org >>>>>> https://www.ietf.org/mailman/listinfo/oauth >>>>>> >>>> >>>> >> >> _______________________________________________ OAuth mailing list OAuth@ietf.org https://www.ietf.org/mailman/listinfo/oauth
