Film-Tech Forum ARCHIVE: KDM timing question

my profile | my password | search | faq & rules | forum home

»	Film-Tech Forum ARCHIVE » Operations » Digital Cinema Forum » KDM timing question (Page 2)

This topic comprises 2 pages: 1 2

Author

Topic: KDM timing question

Steve Guttag
We forgot the crackers Gromit!!!

Posts: 12814
From: Annapolis, MD
Registered: Dec 1999

posted 10-17-2014 09:30 AM

Is there some goofy 6-hour limit requirement on the TLS session? Subject to interpretation, the keys issued to the "SPB" are supposed to only be valid for 6-hours. So once the show starts, the keys have a 6-hour window for those keys. I'm thinking that may pertain particularly to Enigma based systems the security is handed off to the Link Decryptor.

| IP: Logged

Carsten Kurz
Film God

Posts: 4340
From: Cologne, NRW, Germany
Registered: Aug 2009

posted 10-17-2014 09:57 AM

quote: Frank Angel was the last to post
If the right to play a title is given via a KDM for a certain time frame, why is there an additional limit imposed by the "player?" Seems the KDM should be valid no matter how the title is programmed at the site.

But that is not the case?! The 6hr limit only extends the issuer allowed KDM window into the future for pragmatic reasons - the reason is - no lost shows, or no interrupted shows. This is clearly a feature in favor of the exhibitor, so he has an extended safety window e.g. for intermissions or shifts of showtimes or secure clocks.

If a server would adhere strictly to KDM imposed timeframe, it would be a disantvantage, because the KDM issuing entity can never know in advance which complications could arise on site. The idea is, once a show is started, it should proceed until the end of the feature in order to protect the expectation of the audience and to reduce the danger of having to refund.

- Carsten

| IP: Logged

Marcel Birgelen
Film God

Posts: 3357
From: Maastricht, Limburg, Netherlands
Registered: Feb 2012

posted 10-17-2014 10:41 AM

quote: Steve Guttag
Is there some goofy 6-hour limit requirement on the TLS session?

I've never heard about that in particular, but it's not like the DCI specs are so forthcoming in transparency. If it would be, and there is no working infrastructure to renew keys/associations while the feature is playing, it would make any single >6h feature impossible.

We could never have a "The Hobbit - Special Extended Ultimate Edition" or "Transformers 5 - The Director's Ego Cut" in DCP format. At least not as a single feature... shocking. [Wink]

And what Carsten said: If anything besides your customers is limiting you from building a playlist as long as you want, it's for once, not the DCI police's fault, but your server/IMB manufacturer's.

| IP: Logged

Carsten Kurz
Film God

Posts: 4340
From: Cologne, NRW, Germany
Registered: Aug 2009

posted 10-17-2014 11:35 AM

quote: Steve Guttag
Is there some goofy 6-hour limit requirement on the TLS session? Subject to interpretation, the keys issued to the "SPB" are supposed to only be valid for 6-hours. So once the show starts, the keys have a 6-hour window for those keys.

Wouldn't that (literally ;-) at the same time mean you could never pause a playlist for more than 6hrs on an HD-SDI/Enigma system no matter how long the playlist or the KDM window were? That could be easily tested.

- Carsten

| IP: Logged

Marcel Birgelen
Film God

Posts: 3357
From: Maastricht, Limburg, Netherlands
Registered: Feb 2012

posted 10-17-2014 12:06 PM

Yeah, that SHOULD have exactly the same result. Maybe you should switch off your lamp though, it's a bit of a waste otherwise...

But then again, DCPs do their best to mimic film with terms like "reels"... After 6 hours you just run out of virtual platter space! [Smile]

| IP: Logged

Tim Sherman
Expert Film Handler

Posts: 125
From: North Ridgeville, OH, USA
Registered: Aug 2000

posted 10-17-2014 12:54 PM

Just ran a test of 6 movies last night in one spl with the lamp turned off. The show ran for 8 hours and 41 minutes till the end of the playlist without problem. So at least on Doremi Showvault/IMB 8+ hour shows aren't an issue as long as KDMs aren't expiring within that time frame.

| IP: Logged

Steve Guttag
We forgot the crackers Gromit!!!

Posts: 12814
From: Annapolis, MD
Registered: Dec 1999

posted 10-17-2014 01:01 PM

Perusing the DCI specifications. You have :

quote:
9.4.3.5.7. Perform remote Secure Processing Block (SPB) and Screen Management System (SMS) authentication through Transport Layer Security (TLS) session establishment, and maintain the certificate lists so collected.
a.
Associate certificate lists with TDLs delivered in KDMs per Section 5.2.5 of the KDM specification (SMPTE430-1: D-Cinema Operations - Key Delivery Message) to support the identification of security devices that are trusted/not trusted.
b.
Maintain TLS sessions open for not more than 24 hours between complete restarts (i.e., forces periodic fresh TLS keys).

Which seems to ensure that you have a maximum of 24-hours in a TLS session so there is an absolute limit there. Elsewhere, they discuss that after a reboot it has to do the whole security check.

But here is one that may fall victim to interpretation:

quote:
9.4.3.5.9

Prepare and issue content keys to Media Decryptor (MD) and Forensic Marking (FM) SEs as may require keying per the CPL. Constrain use of keys to:

b. Usage validity periods of six (6) hours for remote SPBs (in line with the rule of item 2c above).

Item "2c" refers to the situation where if a show starts with a valid key, it is to be allowed to continue for up to 6-hours.

But "usage validity periods" could easily be read as meaning that is how long a key is to be allowed to be valid (within the SPB).

| IP: Logged

Carsten Kurz
Film God

Posts: 4340
From: Cologne, NRW, Germany
Registered: Aug 2009

posted 10-17-2014 01:18 PM

Well unlike the KDM expiration window this doesn't necessary mean that playback or pause would need to be broken after 6 hrs - only that a new session would have to be opened. Couldn't the server handle this transparently - if it enforces it at all.
One could look at the CTP as well, but I can't remember having seen something like that.

Well, hardly an issue under real-world conditions anyway, and rather easy to test over night.

- Carsten

| IP: Logged

Steve Guttag
We forgot the crackers Gromit!!!

Posts: 12814
From: Annapolis, MD
Registered: Dec 1999

posted 10-17-2014 04:11 PM

The problem would be when the TLS session is broken/restarted...the show would stop. Why not just put the shows on the schedule back-to-back-to-back rather than one large show (to make a 6-hour performance. What theatre doesn't want periodic breaks to "lets all go to the lobby." Who's bladder is so good that they want to hold it for 6-hours?

| IP: Logged

Philip Jones
Film Handler

Posts: 90
From: England
Registered: Dec 2011

posted 10-17-2014 04:13 PM

the only time we've had a very long show was with the final Twilight film when we did a Marathon of the previous 4 culminating with the last one at midnight.

the first 4 films were sent as a single clip and midway through one of them (can't remember how far in it was now) the picture went off but the sound continued. it came up with a Mediablock disconnected error and we had to do a server restart to get things back on properly.

could this have been related to this 6 hour thing?

| IP: Logged

Carsten Kurz
Film God

Posts: 4340
From: Cologne, NRW, Germany
Registered: Aug 2009

posted 10-17-2014 05:06 PM

It could be, from what Steve describes, but on a long continued program like this, it could just as well have been the occasional hickup.

It could easily be tested over night, with the lamp being off.

It's true, though, that the show may not actually stop but only the picture will vanish. I remember that when I recently played with the Doremi and NC900C with HD-SDI/Enigma, I sometimes pulled out the ethernet cable from the projector. I don't know currently wether I had encrypted content running - but I think the audio continued, the picture went black, and the Doremi indicated a 'connection lost'.

Steve is right in that normally you would do something like this with normal single feature SPLs and scheduling.

Of course, that wouldn't work if you intentionally want to spread the key expiration window for one of these features appearing in the later schedules, because scheduling does not keep the keys from expiring after the assigned validity window ;-)

- Carsten

| IP: Logged

Marcel Birgelen
Film God

Posts: 3357
From: Maastricht, Limburg, Netherlands
Registered: Feb 2012

posted 10-19-2014 09:37 AM

quote: Steve Guttag
The problem would be when the TLS session is broken/restarted...the show would stop. Why not just put the shows on the schedule back-to-back-to-back rather than one large show (to make a 6-hour performance. What theatre doesn't want periodic breaks to "lets all go to the lobby." Who's bladder is so good that they want to hold it for 6-hours?

It doesn't really make sense to have one >6h feature. So, besides the oddball situation where somebody manages to put a few movies back to back into a single feature (apparently studios manage to do so, at least according to Philip), you would never encounter the problem in production. It's still interesting to know though.

I guess this "limited time-frame of TLS session validity", if it's true (because like you pointed out, the specs are at least a bit ambiguous here), has probably been implemented as a security measure, to avoid data being transferred with the same session key for too long...

Newer implementations of TLS support a "New Session Ticket" extension to the TLS protocol. This allows a renewed key exchange on an open session. Some "SSL VPN" implementations actively use it. It eliminates some overhead, especially over public IP links, but still, the key exchange will introduce some interruption in the actual stream and given the fact that you cannot really buffer much data without causing inherent latency issues, this will probably also cause some noticeable hickups/frame drops if it's actually implemented.

| IP: Logged

All times are Central (GMT -6:00)

This topic comprises 2 pages: 1 2

Printer-friendly view of this topic

The Film-Tech Forums are designed for various members related to the cinema industry to express their opinions, viewpoints and testimonials on various products, services and events based upon speculation, personal knowledge and factual information through use, therefore all views represented here allow no liability upon the publishers of this web site and the owners of said views assume no liability for any ill will resulting from these postings. The posts made here are for educational as well as entertainment purposes and as such anyone viewing this portion of the website must accept these views as statements of the author of that opinion and agrees to release the authors from any and all liability.