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I would like to mount a Truecrypt container over a VPN connection. The VPN connection averages 0.4Mb/sec in either direction.

Does Truecrypt add a significant overhead (in terms of bytes) to reads/writes that make mounting a container through a slow connection unfeasible? Or would the bytes read/written, for a particular activity, be largely the same as reading/writing directly to a Windows share?

In case it helps, I am trying to come up with a remote backup solution that encrypts the data but still allows for "difference only" backups. My idea is that I open a remote Truecrypt container and then use something like Robocopy to sync the contents of the container with some local data.

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This is exactly what I want to do as well. And if could work over sftp that would be good – Tom Jenkinson Mar 27 '13 at 9:02

Apparently you answered your own question by making your own tests, which by the way, have been very informative for me since I'm currently evaluating a very similar solution to yours. I also wanted to add something that you may have already considered, but didn't mention in your original answer: the performance of the solution will probably depend not only on the upload and download speeds of the link, but also on its latency. A very high latency link would possibly make the solution unusable. Did you finally complete your tests? Are you currently using this solution for your backups?

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Unfortunately I never did that final test, as I decided not to bother with this backup method. – James Mar 13 '12 at 10:27
@city_zen did you get this working for your backups. I want to mount a true crypt container from a network drive (preferably over sftp) – Tom Jenkinson Mar 27 '13 at 9:06

I decided to "pull my finger out" and do my own tests.

First I created a 50MB Truecrypt container and copied it to my remote node (standard Windows copy to a Windows share). The copy achieved an average speed of 59 KB/second.

I tried opening the remote TC container and this worked, with a delay of a few seconds while the mounting process completed.

I then tried copying a 25MB file into the TC drive. The file copy progress moved to 99%, paused for a few seconds, and then the copy dialog disappeared.

I checked the upload speed in the Hamachi (VPN) client. It showed a steady 60KB/second, so presumably the Truecrypt client pipelined the file and then transferred the encrypted blocks to the container in the background.

While this background transfer was under way I tried dismounting the drive in the Truecrypt client. The client froze but did not crash. I kept an eye on the Hamachi client and as soon as the network traffic dropped the TC drive was dismounted and the client started responding again.

I remounted the container and copied 25 small files, totalling 13MB, into the TC drive. Again, the copy dialog disappeared immediately but Hamachi showed that the Truecrypt client was transferring the encrypted files in the background.

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The connection is slow which gets me to believe that the round trip time will be bad as well. Using truecrupt on top of it won't help.

Even if I had loads of truecrupt over slow network expierience it would be hard to answer the question without knowing how large the container is and how you acess the data on it (how many reads and writes and how time critical those are)

For example:

  • If you use this setup to load some ssh keys once into ram and use them for as long as the session lasts it will probably work (small data few reads/writes)
  • If you plan execute a tool that reads and writes a lot it probably won't. (much data read/written often)
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You make a good point when you say "how many reads and writes and how time critical those are". I will rephrase my question a bit. – James Oct 11 '11 at 10:00

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