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Let's say I have daily files that need to be encrypted using PGP (and then emailed) and I want to automate this task. I would be using Windows PowerShell to manipulate the files (examine date/times etc), but how can I automate the PGP part?

I am using the PGP software manually, but I do not see any command line options. I do see a command line software from the same place (Symantec) but for $3000 which I can't do.

I found GnuPG, but (according to GnuPG's FAQ) PGP cannot decrypt GnuPG files if using v 2.x or if using v 5.x then PGP has to use more options. The receiving users are not be willing to make things more complex with extra options required.

In short, I am looking for a command line PGP for Windows.

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2 Answers

up vote 8 down vote accepted

The incompatibility is only for v2.x of PGP. For v5.x, the GPG (not PGP as you state) needs to have more options.

If the problem with PGP 2.x is truly an issue, then you will probably have to shell out for the PGP command-line version. Note that PGP v5 appears to have been released in 1997 and PGP v2 was in 1992-ish, so unless you are dealing with recipients that do not upgrade, you will probably have good coverage.

Import your key and others:

gpg -v --import c:\pgp\my-pub-and-priv-pgp-key.asc

Import each recipient key

gpg -v --import c:\pgp\pub\recipient1.asc
...
gpg -v --import c:\pgp\pub\recipientN.asc

For some reason the command-line options are really hard to find in the locally installed Windows manual; here they are.

Now use --batch for batch mode, --passphrase-file to have your private key unlocking phrase read from the given file instead of from the keyboard via the gpg-agent*, and always trust the recipient keys. If you don't need to have the output signed, then obviously you won't need to use or unlock your private key.

Encrypt (-e) and sign (-s) a file

gpg -v --always-trust --batch --passphrase-file mypassphrasefile -se -r recipient1 -r recipient2 ... -r recipientN -o output-file file-to-encrypt

Files should be able to be decrypted and verified with PGP by the recipients.

*I don't think I have to say what kind of potentially bad idea it is to store your private key passphrase in a cleartext file. Note that on Windows, the gpg-agent will read your private key from the keyboard and cache it. The time period it caches it for can be set in the gpg-agent.conf file, though I've not tried this (see here for some potential pointers; the gpg-agent.conf resides in your home dir which is set using the GNUPGHOME env var or by setting the HKCU\Software\GNU\GnuPG:HomeDir string variable).

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I would recommend that you use GPG on your side and use the self-decrypting archive option. You would need to use GPG on a Windows box on your side and you would just need to attach a password. Might have to play with it for a while as I have not done it in a number of years.

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A PGP key is required (and is used by the current method with PGP software) by the receiving users. I can't add anything on like a password; or is there a way to handle it the same way? –  JBurace Feb 28 '12 at 2:25
2  
Self-decrypting archives are a bad security practice (they train people to run .exe files they got in their email, or whereever) and should be obliterated. –  D.W. Feb 28 '12 at 21:07
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