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9 Decrypting e-mails, practicing for OpenPGP

Gpg4win, the certificate of your key pair and of course your passphrase are all you need to decrypt e-mails.

This Chapter shows you step for step how to decrypt e-mails in Microsoft Outlook using the Gpg4win program component GpgOL.

Initially, you can practice this process with Adele and your public OpenPGP certificate. The following exercises again only apply to OpenPGP - explanations regarding the decryption of S/MIME e-mails can be found at the end of this chapter on page X.

In Section 8.1 you sent your public OpenPGP certificate to Adele. Using this certificate, Adele will now encrypt an e-mail and send a message back to you. You should receive Adele's response after a short time period.

Decrypting a message with MS Outlook and GpgOL

Most e-mail programs also have special program extensions ("plugins"), which can be used to perform the encryption and decryption process directly in the e-mail program. GpgOL is such a program extension for MS Outlook, which is used here to decrypt Adele'se-mails. For more information on other software solutions, please see Annex 25.4. You can read this section now, or later when you need this function.

Start MS Outlook and open Adele's response e-mail. Until now, you have only known Kleopatra as a certificate administration program. However, the program can do much more than that: It can control the actual GnuPG encryption software and hence not just manage your certificates but also take care of all cryptographic tasks (with GnuPG's assistance). Kleopatra provides the visual user interface, hence the dialogs which you as the user see while you encrypt or decrypt e-mails.

Hence Kleopatra processes Adele's encrypted e-mails. These e-mails have been encrypted by Adele using your public OpenPGP key.

To decrypt the message, Kleopatra will now ask for your passphrase that protects your private key. Enter your passphrase.

The decryption is successful if you do not see an error dialog! You can now read the decrypted e-mail.

You can retrieve the exact results dialog of the decryption by clicking on Extras -> GpgOL decryption/check in the menu of the opened e-mail.

However, surely you also want to see the result, namely the decrypted message ...

The decrypted message

Adele's decrypted response will look something like this4:

Hello Heinrich Heine, 

here is an encrypted response to your e-mail. 

I received your public key with the key ID 
FE7EEC85C93D94BA and the name
`Heinrich Heine <heinrich@gpg4win.de>'.

Attached is the public key of adele@gnupp.de,
the friendly e-mail robot.


The text block that follows is Adele's public certificate.

In the next chapter, you will import this certificate and add it to your certificate administration. You can use imported public certificates at any time to encrypt messages to the people you are corresponding with, or to check their signed e-mails.

In short:

  1. You have decrypted and encrypted an e-mail using your private key.
  2. Your correspondence partner has attached his own public certificate, so that you can answer him in encrypted form.

e-mail decryption using S/MIME

So this is how e-mails are decrypted using the private OpenPGP key - but how does it work with S/MIME?

The answer: The same!

To decrypt an encrypted S/MIME e-mail, simply open the message in Outlook and enter your passphrase in the pin entry dialog. You will see a status dialog that is similar to that shown for OpenPGP. After closing this dialog, you will see the decrypted S/MIME e-mail.

Differently from OpenPGP decryption, however, when using S/MIME you cannot use Adele to practice, since Adele only supports OpenPGP.

© 31. August 2010, v3.0.0-beta1 (last minor changes from 21. September 2010)
The Gpg4win Compendium is filed under the GNU Free Documentation License v1.2.

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