KMail/PGP MIME

Mettre en place la signature des message en utilisant GPG dans KMail

de Fajar Priyanto, 2004

Créer, sauvegarder, et publier votre clé

1. Vous allez avoir besoin d'utiliser le programme gpg. Il est normalement déjà installer par défaut.

2. Créer votre propre clé (taper ça à votre compte utilisateur, et pas root) :

gpg --gen-key

Suivez les instructions, elles sont très claires et faciles.

3. Vérifier que la clé est créée :

gpg --list-key

Vous allez voir quelque chose comme ci-dessous avec vos informations :

:pub 1024D/85EEC6A5 2004-03-15 Fajar Priyanto (Knowledge is power! http://linux.arinet.org) sub 1024g/BBBB57F3 2004-03-15

4. Look at the above details. For example 85EEC6A5 is your key ID. Now, in order to export your public key:

:gpg -ao fajar-pub.key --export 85EEC6A5

A file called fajar-pub.key will be created in the current directory. This is a copy of your public key. This is also the file that people must import to verify your signed emails. You can publish it in keyservers around the world, or you can send it directly to the people requesting it, or you can place it in your website for others to download.

Si vous regardez à l'intérieur du fichier, le contenu ressemblera à ça :

-- --BEGIN PGP PUBLIC KEY BLOCK-- --

Version : GnuPG v1.2.3 (GNU/Linux)

mQGiBEBVTw8RBACaYvnDkgqNWyktg3urdE9mrpv63x3Iux2zVkuZk8pIRp5HeR/V

[snip snip...]

B394acuU4FdGN/EynYUAn1aRvNmgs0/IU2MDzYQpbHIaqpkE

=B0cy

-- --END PGP PUBLIC KEY BLOCK-- --

Also, you might want to back up your secret key to a secure medium (not just one floppy: this will get damaged), you can use the following command:

$ gpg -ao secret.asc --export-secret-keys 85EEC6A5

This will create a textfile containing your secret or private key, with the filename secret.asc. Do not hand it to someone you do not trust 100%. Hide it in a safe place (or better, more than one).

Finally, it is advisable to generate a revocation certificate and store it in a safe place away from your secret key. In case your secret key gets into the wrong hands, you can revoke it so it can not easily be abused by others. The command to do this is

$ gpg -a -o revoker.asc --gen-revoke 85EEC6A5

Ceci vas créer un fichier texte avec le nom revoker.asc qui contient le certificat de révocation.

Setting up Kmail to sign emails using your gpg key

1. Fire up Kmail, and go to Settings -> Configure KMail -> Identities
2. Choose the identity that you are using
3. Then click Modify -> Cryptography -> OpenPGP signing key
4. It will automatically show your gpgkey, that is 85EEC6A5
5. If it will not, click Change..., choose key ID then click OK
6. Now, set up Kmail to automatically sign all emails that you write using your key
7. Still in the Kmail Configure menu, go to Security -> Composing
8. Tick mark these:
   1. Store sent messages encrypted,
   2. Always show the encryption key for approval,
   3. Automatically sign messages
9. Exit the configuration menu by clicking OK.

Testing Kmail by creating a new message

1. You will notice that there is a Sign Message icon right after the paperclip (attachment) icon. It's already active.
2. Write your message and when you are done, send it.
3. Kmail will ask for you to type the secret passphrase that you made during the gpg --gen-key step. Type it in, and then Kmail will show you a confirmation window of the signed message. Click OK to send it.
4. If you test it by sending to yourself, you will notice that Kmail displays the message with a GREEN header, with words like this: Message was signed by Fajar Priyanto (Knowledge is power! http://linux.arinet.org) (Key ID: 0x85EEC6A5). The signature is valid and the key is ultimately trusted.
5. People that have your public key will have that display also, but those who don't have the key, will have the message displayed in yellow with words like this: Message was signed with unknown key 0xBFE7357F. The validity of the signature cannot be verified.

FÉLICITATIONS

You now can communicate in a more secure way if you want to. I know this how-to is very short and might not be very clear. Well, please give me suggestions and I will improve it when the time comes. Also I intend to write the second part of this topic which covers how to ENCRYPT messages, import other public keys, and install Crypto Plug-ins. Special thanks to Tim Sawchuck and Philip Cronje and all my friends in the Mandrake List.

Problèmes

• Messages signed by a key already known display correctly in KMail, but new keys were not being imported, and you can't sign messages. The culprit is a missing package. Installing pinentry-qt (you may need pinentry-qt4) appears to solve both problems.

• KMail no longer does in-line signatures. OpenGPG has to be used instead. KGpg is a useful applet that helps in the management of signatures, both your own and those collected.

• If OpenGPG is functioning correctly you will have to give the pass-phrase every time you send a document that is to be signed. This soon becomes a pain, and the way out of that is to configure gpg-agent, which comes with kdebase-common package. Unfortunately, the install does not pick up the need for pinentry-qt(4) or pinentry-gtk (KDE or GNOME), so that has to be installed separately. The config file for gpg-agent is written to by KMail's settings.

Note

To be sure the "passphrase agent" (gpg-agent) is enabled, check your ~/.gnupg/gpg.conf and eventually uncomment the line containing "use-agent".
In KMail's Settings -> Configure KMail -> Security tab -> Crypto Backends, select OpenGPG, then Configure. On the GPG Agent page, give a path to which logs can be written, in case of problems. You can check the log in KMail's Tools -> GnuPG Log Viewer. It's probably a good idea, too, to increase the cache time - I use 3600.

Warning

The following startup and shutdown scripts may be already in use from your distro, but not written in this path. Do not install these scripts unless you have problems with startup and shutdown

• If you do not have it already, in ~/.kde create a directory called env. In there, create a file called gpgagent.sh containing

#!/bin/bash
killall gpg-agent
eval `gpg-agent --daemon`

Save it and make it executable.

In the same way you would clean up gpg-agent on shutdown, so if you do not have it already, create another directory called shutdown into ~/.kde and create in it another script file called stop_gpgagent.sh containing

#!/bin/bash
killall gpg-agent

Save it and make it executable.

Troubleshooting Tips

ps -edalf | grep gpg-agent

va lister toutes les instances de gpg-agent.

killall gpg-agent

stops all instances

eval "$(gpg-agent --daemon)"

will restart the agent

gpg-agent status

should tell you if the agent is running.

Voir aussi :

La page de présentation a plus d'astuces.