Tivo: Please weaken your encryption

[mikesown]

Tivo,
Thank you a lot for releasing TTG/MRV. A lot of us have eagerly been awaiting these features. The main problem with them currently is that the transfers are very slow. A tenth of what they should be. No doubt some of this is due to the fact that the Tivo can't buffer two HD streams and transfer a third off with a great deal of speed. However, due to the speed of today's hard drives, I can't help but think that the majority of this is due to the encryption that is being applied on-the-fly to the file. I bring to your attention the following two points:

1. QAM signals are not being decoded in any way by the CableCards. Thus, you do not need to protect these recordings.

2. The TTG encryption has already been broken. It is no secret how to decrypt a .tivo file.

Thus, I propose the following suggestions for you:

1. Disable on-the-fly encryption altogether for QAM/OTA recordings. This is unnecessary overhead for content that does not need to be protected.

2. Weaken(computationally) the encryption for other types of recordings. No doubt CableLabs wants some sort of encryption on the file, but it need not be so much that the Tivo can't output a stream of HD at 70 megabits per second. Keeping in mind that the current encryption has already been broken, this idea is not so hard to swallow. Simply propose the new encryption as a more efficient means of encoding copy-protected data. Also, keep in mind that any new encryption that is introduced will be broken. Thus, you need only be worried about your users; you will never be able to fully serve CableLabs' interests regardless of encryption method chosen.

Sincerely,
Mike

[Dan203]

TiVo does NOT do "on-the-fly encryption". The encryption in TiVo files is applied at record time using dedicated hardware and has absolutely no impact on performance. The reason TTG is slow is because natively TiVo stores video and audio in a specialized stream format known as a TY stream. These streams are similar to MPEG-2 transport streams in that they are designed for realtime recording and playback. For compatibility reasons TiVo converts the TY stream into a standard MPEG-2 program stream on-the-fly for TTG. This is what causes the slowdown.

Trust me the S3/HD units are 10 times faster when it comes to TTG then the old S2 units. I have a Toshiba DVD/TiVo unit that takes more then realtime to transfer a High quality recording which is only about 6Mbps. My S3 TiVos can transfer HD material, which is closer to 15Mbps in about 1/3 realtime which is a huge step up if you ask me.

Also, FYI, the QAM signal is being decrypted by the CableCARD(s) before the video stored on the TiVo. In fact it's a requirement of the CableCARD specification that any device intending to store that decrypted content, such as a DVR, has to apply it's own "approved" encryption scheme to the content before storing it on disk.It's a common misconception that CableCARDs decrypt content during playback, but in fact the decrypt at transmission time and from there it's the responsibility of the device to protect the content. That's why there is such a rigorous approval process to get a device CableCARD certified and why CableLabs was able to prevent TiVo from releasing TTG and MRV on the S3/HD units for so long.

Dan

[gonzotek]

Also, FYI, the QAM signal is being decrypted by the CableCARD(s) before the video stored on the TiVo. In fact it's a requirement of the CableCARD specification that any device intending to store that decrypted content, such as a DVR, has to apply it's own "approved" encryption scheme to the content before storing it on disk.It's a common misconception that CableCARDs decrypt content during playback, but in fact the decrypt at transmission time and from there it's the responsibility of the device to protect the content. That's why there is such a rigorous approval process to get a device CableCARD certified and why CableLabs was able to prevent TiVo from releasing TTG and MRV on the S3/HD units for so long.

DanAlthough the OP didn't explicitly state so, I think he was talking about the 'in the clear' QAM channels that can be received without a cable card by (for example) many digital tuner tvs.

[mikesown]

TiVo does NOT do "on-the-fly encryption". The encryption in TiVo files is applied at record time using dedicated hardware and has absolutely no impact on performance. The reason TTG is slow is because natively TiVo stores video and audio in a specialized stream format known as a TY stream. These streams are similar to MPEG-2 transport streams in that they are designed for realtime recording and playback. For compatibility reasons TiVo converts the TY stream into a standard MPEG-2 program stream on-the-fly for TTG. This is what causes the slowdown.

Trust me the S3/HD units are 10 times faster when it comes to TTG then the old S2 units. I have a Toshiba DVD/TiVo unit that takes more then realtime to transfer a High quality recording which is only about 6Mbps. My S3 TiVos can transfer HD material, which is closer to 15Mbps in about 1/3 realtime which is a huge step up if you ask me.

Also, FYI, the QAM signal is being decrypted by the CableCARD(s) before the video stored on the TiVo. In fact it's a requirement of the CableCARD specification that any device intending to store that decrypted content, such as a DVR, has to apply it's own "approved" encryption scheme to the content before storing it on disk.It's a common misconception that CableCARDs decrypt content during playback, but in fact the decrypt at transmission time and from there it's the responsibility of the device to protect the content. That's why there is such a rigorous approval process to get a device CableCARD certified and why CableLabs was able to prevent TiVo from releasing TTG and MRV on the S3/HD units for so long.

Dan
Fair enough. A few points:

1. When I was refering to QAM, I meant 'in-the-clear' QAM which can be received without a CableCard.

2. I was not aware that the shows were stored in an encrypted format on the Tivo itself. Wouldn't this contribute to the slowness of the Tivo HD?

3. Is there any technical reason why the shows cannot be transfered demuxed? You stated this could not be done for 'compatibility' reasons, which seems a bit vague. It appears to me that a direct hard-drive to network transfer would not consume a lot of processing power on the Tivo, and would result in significantly higher transfer rates.

[mikeyts]

As I understand it (from a friend who works on TiVo), both the encryption and decryption of video is performed by the Broadcom chipset; the chipset used in TiVo HD is newer and a bit more capable than the one in TiVo S3, and probably does the decryption faster, if anything. It doesn't matter how fast it is, as long as it's faster than broadcast bit rates, which are pretty frickin' pedestrian, limited to 19.39 Mbps. HDMI/HDCP chipsets have to encrypt and decrypt data flowing at Gbps rates.

What do you mean by "demuxed"? Also, I spent 15 year working on firmware in networking equipment, although that ended 6 or 7 years back; I'm unware of any "direct hard-drive to network" transfer mechanisms.

[greg_burns]

3. Is there any technical reason why the shows cannot be transfered demuxed? You stated this could not be done for 'compatibility' reasons, which seems a bit vague. It appears to me that a direct hard-drive to network transfer would not consume a lot of processing power on the Tivo, and would result in significantly higher transfer rates.

You can grab the .ty files directly with a "hacked" tivo. (And yes it much faster to transfer them to your PC from what I've read, no personal experience though). Can you hack an S3? I don't know.

I assume compatibility reasons means, most people wouldn't be able to play the raw files (.ty?) coming from a tivo without using software to mux them on the PC side. Would that be better use of resources? Sounds like it to me, even if it meant it was more complicated.

my .02

[mikesown]

As I understand it (from a friend who works on TiVo), both the encryption and decryption of video is performed by the Broadcom chipset; the chipset used in TiVo HD is newer and a bit more capable than the one in TiVo S3, and probably does the decryption faster, if anything. It doesn't matter how fast it is, as long as it's faster than broadcast bit rates, which are pretty frickin' pedestrian, limited to 19.39 Mbps. HDMI/HDCP chipsets have to encrypt and decrypt data flowing at Gbps rates.

What do you mean by "demuxed"? Also, I spent 15 year working on firmware in networking equipment, although that ended 6 or 7 years back; I'm unware of any "direct hard-drive to network" transfer mechanisms.
Sorry for not being more clear. I was referring to a transfer done without any transformation of the file, akin to doing an ftp file transfer of a file on my computer to another computer on my LAN. In this case, there is very little CPU overhead(as no file transformation is being done).

In my experience, it's not any faster. (Unless you pull the drive and put it in your PC.) However, I've never compared TTG and transferring .ty from the same machine -- I've done the former only on S3's, the latter only on DirecTivos.

This would be a very interesting claim to evaluate. Does anyone have a hacked S3/THD with TTG to do a comparison?

[classicsat]

I suspect they are doing the muxing in the TiVo for security purposes. If they did it in the PC, it might be easier to break. Plus they can watermark it at the muxing stage (if it isn't already).

As for why encrypt TiVo transfers all the time; it is most content is copyrighted content, regardless of the manner it was received, hence it is practically TiVo's duty to do what they can to ensure its protection, so all TiVo transfers are encrypted just the same. As for the algorithm being public, well, it is not widely known, or to my knowledge being "abused".

[mikesown]

I suspect they are doing the muxing in the TiVo for security purposes. If they did it in the PC, it might be easier to break. Plus they can watermark it at the muxing stage (if it isn't already).

Keep in mind that the encryption is already broken. Changing the location of encryption should not affect the "security" as of now.


As for why encrypt TiVo transfers all the time; it is most content is copyrighted content, regardless of the manner it was received, hence it is practically TiVo's duty to do what they can to ensure its protection, so all TiVo transfers are encrypted just the same.
Yes, content is copyrighted. However, copyright law(in the US) allows a user to make copies for personal use. It is not Tivo's duty nor responsibility to ensure that a user only copies content for personal use for non-DRMd content.

CableLabs content is another matter entirely. In this situation, I would suggest Tivo go to CableLabs and propose the use of an encryption method which is more computationally-efficient.


As for the algorithm being public, well, it is not widely known, or to my knowledge being "abused".
The algorithm is publicly documented not only by so called "hackers," but also by a very large company who originally developed the algorithm. The company provides free source and documentation to the algorithm, even to commercial products. To say that it is not widely known is a huge understatement.

Disclaimer: I am not a lawyer of any sort. This is not legal advise of any kind, and should not be taken as such.

[jebbbz]

...Also, FYI, the QAM signal is being decrypted by the CableCARD(s) before the video stored on the TiVo. In fact it's a requirement of the CableCARD specification that any device intending to store that decrypted content, such as a DVR, has to apply it's own "approved" encryption scheme to the content before storing it on disk.It's a common misconception that CableCARDs decrypt content during playback, but in fact the decrypt at transmission time and from there it's the responsibility of the device to protect the content. That's why there is such a rigorous approval process to get a device CableCARD certified and why CableLabs was able to prevent TiVo from releasing TTG and MRV on the S3/HD units for so long.



Is there any particular reason for CableCARDs to operate like this? Could a device be designed to simply write the cableco-encrypted content to a hard drive, first wrapping in it a container with the program metadata and then perform the CableCARD decryption during playback? Presumably the video out would have to be integral to the device so there would not be an unencrypted digital stream wandering around loose.

I began wondering about this when AMD/ATi offered their digital cable tuner that could not be used with anything but a new, OEM-only PC with a special BIOS and version of Vista, etc. It seemed this was made necessary precisely because the cableco encryption was stripped off by the CableCARD during reception, not playback. If the AMD/ATi offering instead had been an "All-In-Wonder" with the video out built in it might be able to perform as I have tried to outline and CableLabs approval would be needed only for the expansion card rather than a whole PC and OS since unencrypted data would never leave the CableCARD-hosting video I/O card.

Is there something about the cableco encryption method that renders it unsuited to a TiVo or a TiVo-like device? Obviously, TiVo now has its own CableLabs-approved encryption so this is a bit academic but back in the days of the S1 I wondered if they could have offered a TiVo expansion cards for PCs, even if they required a dedicated hard drive for the TiVo file format.

[Dennis Wilkinson]

Keep in mind that the encryption is already broken. Changing the location of encryption should not affect the "security" as of now.

This is picking nits, but strictly speaking, the encryption has not been broken. All of the currently available techniques for removing the encryption require the key (via the MAK). If the encryption were truly broken, then anyone could decrypt anyone else's .tivo files, which isn't the case.

Yes, content is copyrighted. However, copyright law(in the US) allows a user to make copies for personal use. It is not Tivo's duty nor responsibility to ensure that a user only copies content for personal use for non-DRMd content.

Nor is it their responsibility to make it easier for you to do so. It is in alignment with their business goals, though (their pockets are not deep enough to cover the lawsuits that would almost certainly follow, and since they do some partnering with the networks it is in their best interest not to be too big a thorn in the network's side.)

IANAL, but US copyright law also doesn't explicitly support "making copies for personal use", either, whether you're talking about the law as written or the case history in the courts (that's certainly not the scope of the Sony decision.)

[bicker]

Yes, content is copyrighted. However, copyright law(in the US) allows a user to make copies for personal use. That is not the case. Read the law again.

You're probably mistaking the special exclusion for computer software.

It is not Tivo's duty nor responsibility to ensure that a user only copies content for personal use for non-DRMd content.TiVo's responsibility includes everything they personally subscribe to.

Disclaimer: I am not a lawyer of any sort. This is not legal advise of any kind, and should not be taken as such.Good thinking.

[JamieP]

TiVo does NOT do "on-the-fly encryption". The encryption in TiVo files is applied at record time using dedicated hardware and has absolutely no impact on performance.This is simply not true for TTG. Hardware encryption is used for normal on-disk storage of recordings, but when transfered via TTG, the recordings are decrypted and reencrypted with a completely different encryption algorithm, and the reencryption is all done in software using significant CPU resources. If you have a hacked tivo, you can verify this by statistical profiling (PC sampling).

...
The reason TTG is slow is because natively TiVo stores video and audio in a specialized stream format known as a TY stream. These streams are similar to MPEG-2 transport streams in that they are designed for realtime recording and playback. For compatibility reasons TiVo converts the TY stream into a standard MPEG-2 program stream on-the-fly for TTG. This is what causes the slowdown.
As you say, the Series3 and TiVoHD store the video stream in a format that is essentially an mpeg transport stream. How about allowing a "native" TTG transfer to PC that preserves the transport stream format, rather than converting to a program stream? Many tools (e.g. VideoRedo) can read transport streams. If it really is the stream format conversion, and not the re-encryption, that is using CPU resources, why not leave that to PC side tools?

[Laserfan]

The argument about encryption can (and will no doubt) go-on ad nauseum--but the request in the title of this thread is ridiculous. Does anyone think for one second that Tivo is going to consider changing their encryption methodology to enable folks to transfer shows out-of-it faster? So they can share More (copyrighted) shows Faster with their "friends" and the Internet? Good grief. :rolleyes: