Please allow making a decrypted backup from an encrypted one

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thetoad
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Please allow making a decrypted backup from an encrypted one

Post by thetoad » Mon Dec 04, 2017 11:53 pm

Currently one can also make a backup (even from console app) from a disc drive. One can create an encrpted backup and use that to make mkvs, but not to make a decrypted backup.

why is this neccessary?

some iscs are broken or are difficult to read. ddrescue can recover them. I can then extract the content (assuming its a non bus encrypted drive). can use discatt.dat file created by makemkv in an encrypted backup and place it in the extracted directory, but makemkv refuses to decrypt the content as if it was a disc. I tried including it as a loopback device, but makemkv only sees sg devices.

mike admin
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Re: Please allow making a decrypted backup from an encrypted

Post by mike admin » Wed Dec 06, 2017 8:14 pm

This is exactly how you do it, with BEC or non-BEC drive.
- copy all files from the disc into folder, with copy / ddrescue or whatever
- start a non-decrypted backup with MakeMKV and abort it as soon it starts writing files. The very first file written is discatt.dat, this is made on purpose.
- copy discatt.dat into your folder.

Your folder is now a non-decrypted full disc backup that can be opened with MakeMKV. If you want decrypted M2TS files, then just start streaming and "download" M2TS from built-in webserver. Or compile the libaacs m2ts decryption app and run it with libmmbd.

thetoad
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Joined: Thu Jul 28, 2016 4:18 am

Re: Please allow making a decrypted backup from an encrypted

Post by thetoad » Fri Dec 08, 2017 4:56 pm

why not just make backup work i.e a folder to folder mode? With DVDs I was actually able to do this "in place" (as the crypto is different). I was able to take an ISO I generated (even in the olden days of bad blocks on the disc) and since CSS is basically just scrambling certain blocks, could read the scrambled blocks with decss_read and then just write them out overwriting themselves. Not knowing much about aacs, unsure if that's possible, though considering the moving of the AACS directory, that's probably not possible.

thetoad
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Re: Please allow making a decrypted backup from an encrypted

Post by thetoad » Fri Dec 08, 2017 6:15 pm

Also mike, re bus encryption. Is bus encryption constant (i.e. reading a disc from 2 bus encrypted drives would result in the same bit stream) or is it different from drive to drive?

The reason to ask is sometimes different drives are able to read different parts of the disc with different amounts of ease. (I find this with DVDs a lot, some drives are very good at reading, but are very slow, take a lot of time to reset after a read error, while other drives are not as good at reading, but plow through read errors). So would it be possible to decrypt an ISO created from 2 bus encrypted drives or is the bus encryption data stored in the file (presumambly thats why it works?) specific to the drive it was created with? just wondering. thanks!

mike admin
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Re: Please allow making a decrypted backup from an encrypted

Post by mike admin » Tue Dec 12, 2017 12:49 pm

thetoad wrote:Also mike, re bus encryption. Is bus encryption constant (i.e. reading a disc from 2 bus encrypted drives would result in the same bit stream) or is it different from drive to drive?
No, this is the point of bus encryption. The keys are per drive. You have to read everything on the same drive.

thetoad
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Re: Please allow making a decrypted backup from an encrypted

Post by thetoad » Tue Dec 12, 2017 4:15 pm

what I thought. good reason I've invested in a number of non bus encrypted drives then :)

I'd still like the folder to folder decryption mode if possible. :)

carlalex
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Re: Please allow making a decrypted backup from an encrypted one

Post by carlalex » Fri Sep 07, 2018 3:09 pm

Old thread, but I was also surprised when I found no folder-to-folder mode.

These days, I would consider the 4k/UHD -> MKV rip not truly a lossless one, since MKV currently lacks the ability to store DolbyVision data. Granted, I don't have a way to play it back if it did. What ends up happening is that if I have a disk that isn't in keys_hashed, I make an encrypted backup, and use that backup to create MKVs when the keys become available. But, I keep the backup around should there ever be a day I can preserve the DV data or if I ever wanted to play the disk with menus. It would be super to be able to decrypt that folder-to-folder without having to go back to the disk (which I tend to bury in a box in storage as the backup of last resort.)


--- Carl

P.S. Thanks for all your work maintaining MakeMKV - great software!

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