Encryption (Part 2): How to Back Up Encrypted Files

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Encrypting your PC is one thing, but how do you keep it backed up? And how do you maintain easy access to the files if you work on several computers at different times?

One author I know has two simultaneous book projects going, both of them full of juicy material. He wouldn’t want his notes, drafts or recorded interviews to be cast across the web, but he wants easy access to his files at work and home.

When the author called on CounterSpy recently, he was keeping all his work on one laptop, with a copy on an encrypted thumb drive. (Let’s leave aside the quality of thumb drive encryption. Kingston, SanDisk and Verbatim were badly embarrassed this year when it turned out their allegedly secure products were easy to crack. I’ll soon be reviewing a strong alternative.)

“Where do you keep the thumb drive?” I asked.

“In my laptop bag,” he replied.

“So if you lose one bag, your book is gone?”

“Well, yes,” he said. “That’s what I’m worried about.”

My suggestion: combine Dropbox and Truecrypt to build an automated system of secure backups. Truecrypt provides strong password protection, and Dropbox syncs your secure files automatically, storing copies in the cloud and on updating them on each of your computers. Dropbox handles the backups for you, but you control the encryption. That means nobody at Dropbox, even under court order, can open your secret files. This is as close as you come to having your cake and eating it on CounterSpy. (If you’re a human rights activist in China, and you don’t want anyone to know you use encryption at all, this would not be a great idea. It would be evident to authorities that you’re using TrueCrypt, and that could attract unwanted attention. As always, security depends on the threat.)

Turns out I’m not the first to think of the Dropbox-Truecrypt combo. You can find more detailed discussions of the technique here and here. Pitch in with a comment if you’ve tried this or have a better idea.

Note : Dropbox has to copy the whole file container every time you use it, not just the files you change. And uploads are much slower than downloads. Start with a 10 or 20MB container and see how that goes. I doubt this method will be practical with a container of more than 100MB, so it won’t be much use if you need to encrypt a lot of video or high-resolution photos.

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