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I was hoping to use my Yubikey for file encryption, but also wanted to have a backup Yubikey work to unlock the file.

From a conceptual point of view, I know it is possible since, even as is, I believe many encryptions work by symmetrically encrypting an asymmetric password used to encrypt the rest of the data, so all I would need is multiple encryptions of the asymmetric password for each key.

I'm not sure which tools support this kind of encryption, but was hoping to find a tool that:

  • Supports use of multiple yubikeys
  • Bonus: Works well with cloud storage by encrypting files individually or otherwise breaks up the file into smaller pieces only some of which need to be reuploaded when a file changes.
  • It’s unlikely they would use asymmetric to encrypt the data . It’s more likely they use symmetric. But the rest of what you said makes sense. – ISMSDEV Nov 2 '17 at 17:47
  • @ISMSDEV I was under the impression that most symmetric encryption systems only symmetrically encrypt an asymmetric password used for the rest of the file since symmetric encryption is so much more expensive. Is that not the case? – Dan Nov 2 '17 at 17:53
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    @Dan You've got it backwards, asymmetric encryption is much more expensive. – AndrolGenhald Nov 2 '17 at 18:58
  • @AndrolGenhald Yes, you are right, I was flipping my terms. – Dan Nov 2 '17 at 19:27
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Since Yubikey supports OpenPGP. So yes, you just need to address any messages you encrypt to both the recipients and and the backup key. PGP messages can have multiple recipients.

You'll also need to tell people sending messages to you, to also address your backup key, or to reencrypt their message to your backup key whenever you receive them.

  • The encryption features of the Yubikey isn't PGP specific. – Peter Nov 30 '17 at 20:09
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If you don't require that the key be generated on your Yubikey, you can generate a PGP keypair and copy it to both your primary and backup Yubikeys. Yubico has a how-to on importing keys on their site here.

That being said, from what I've read many people (who I'm sure know something I don't) would try to avoid this, so there may be a good reason not to.

  • There is a value in having keys that have never existed outside the hardware. That way you could be reasonable sure that the file could not have been stolen. But on the other hand, can you trust that there is no flaws in the hardware generating the key? – Peter Nov 30 '17 at 20:07
  • Ah, that makes sense. Thanks. Would this also be why so many people prefer to create their keys inside a live-booted environment? – user8675309 Dec 4 '17 at 22:13

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