GPG decryption via script?

[jasonp45]

I have a PGP-encrypted file which I download and decrypt on my machine (currently via the GPG Windows GUI). Call the file 'MyFile.gpg'.

I want to automate the decryption of this file. However I can't seem to locate a reference detailing the command-line syntax necessary, though I did find the manual here:

http://www.gnupg.org/documentation/manuals/gnupg/.

I'm not sure what the parameters mean or how to structure the statement I'll need. First, is there a reference online simply outlining the command-line syntax for GPG under Windows (the manual I linked seems to be for Linux)?

Second, what is the exact syntax I'd use to decrypt 'C:\MyFile.gpg' to 'C:\MyDecryptedFile.xxx'? How do I point toward my private key? I will ultimately wrap this in a VBScript and will pass my passphrase via an InputBox.

Thanks!

 

[Trevoke]

Well, that's really a question about GPG, not about VBS, isn't it?
First things first.. As I don't use GPG on Windows, first we need to make sure the command-line syntax is similar.

Can you do this?
c:\>...\>gpg --help

And get a help output, or do you get an error? Do of course replace 'gpg' with the name of the actual command-line executable..

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[jasonp45]

Yeah I suppose it is more appropriately a GPG question, though I'm not sure if there's a forum for that?

However my thought was that if anyone had implemented it via command-line they'd do so via either VBScript or a DOS batch file, and since I'm doing the former this seemed the place to post.

Yes, the 'help' syntax you posted works; thanks.

From the GPG directory I ran "gpg -d "C:\MyFile.pgp". It prompted me for my passphrase, then decrypted the file in the command-window.

Not sure from the help items how to:
a) Send the passphrase as a parameter
b) Send the decrypted output to a file

 

[jasonp45]

I got it to output to a file like so:

"C:\Program Files\GNU\GnuPG\gpg.exe" -d "C:\MiFile.pgp" > "C:\MyFile.txt"

Now the only piece of the puzzle is passing the passphrase as a parameter via command-line.

 

[Trevoke]

Yeah, and that's really kinda tricky, since that's really the bit that makes GPG secure.. ;-) You might be able to make GPG somehow wait for input and use some Windows trick to pipe whatever you type into the command line?
On this particular bit, I am out of my league.

Tao Te Ching Discussions : Chapter 9 (includes links to previous chapters)
What is the nature of conflict?

 

[jasonp45]

Got it!

This is the command-line syntax:
"C:\Program Files\GnuPG\gpg.exe" --passphrase "My passphrase" -o "C:\MyFile.txt" -d "C:\MyFile.pgp"

Here is a VBScript example:

Option Explicit

Dim bWaitOnReturn: bWaitOnReturn = True
Dim iWindowStyle: iWindowStyle = 7 'Minimized; active window stays active
Dim sPassphrase: sPassphrase = InputBox("Enter passphrase","Passphrase")
Dim sFileName_Output: sFileName_Output = "C:\MyDecryptedFile.txt"
Dim sFileName_Input: sFileName_Input = "C:\MyEncryptedFile.pgp"
Dim sCommand_Text: sCommand_Text = Chr(34) & "C:\Program Files (x86)\GNU\GnuPG\gpg.exe" & Chr(34) & "--passphrase " & Chr(34) & sPassphrase & Chr(34) & " -o " & Chr(34) & sFileName_Output & Chr(34) & " -d " & Chr(34) & sFileName_Input & Chr(34)
Dim oWiSH_Shell: Set oWiSH_Shell = CreateObject("WScript.Shell")
oWiSH_Shell.Run sCommand_Text, iWindowStyle, bWaitOnReturn
Set oWiSH_Shell = Nothing
WScript.Quit