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Is it possible to have a different passphrase for a GPG subkey?

The reason is that I'm using duplicity to back up my files, and it needs the key passphrase to sign the files.

Since I want run duplicity automatically, I would have to store the passphrase in an environment variable. I don't feel comfortable storing my main key's passphrase in an environment variable, so I'm wondering if I could have a different passphrase for the subkey that does the signing.

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My recommendation is to use a completely separate key. Because you're signing backups, only you need to trust the separate key, so there's not a web of trust issue here. You can even sign it with your main key, if you like.

A second option is to load a gpg-agent and load the key. You'll need to set max-cache-ttl=-1 and default-cache-ttl=-1 to allow it to keep the key indefinitely. You'll still need to type in the passphrase once per boot. (I haven't tested the -1 options, that's based on reading the code that -1 is infinite.)

If you don't want to do that, you could copy your GNUPGHOME (~/.gnupg, typically), delete the other subkeys, and change the passphrase on the key. Then have duplicity use this subkey-only installation with the new passphrase. (Just set the GNUPGHOME environment variable to work with the different home directory.)

  • I'll take your advice and create a separate key, since it will also be easier to manage. Thanks! – LanguagesNamedAfterCofee Jun 10 '14 at 19:01

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