Pretty Good Privacy (PGP) / GNU Privacy Guard (GnuPG)

The KMail Handbook
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# 3.7. Pretty Good Privacy (PGP) / GNU Privacy Guard (GnuPG)

This is a short introduction on how to setup KMail's pgp support. It will give some hints on the use of pgp too. It's written for people who are beginners in this area. If you are familiar with the use of pgp, you can skip most of the steps. Working with GnuPG is generally similar, but some command line parameters may be different. Please also check out the FAQ item about pgp.

| You can encrypt your messages sent with KMail, but this does not mean that the attachments are encrypted. You have to encrypt your attachments manually, using a shell command or some other tool before you attach them.

| KMail has to rely on PGP's output. This output is often different between different version of PGP, so it's important that you test if encryption really works with your setup before you start using it seriously. KMail might not warn you if something fails. You better enable Show ciphered text after composing.

To setup and use pgp support in KMail it is necessary to have pgp installed and set up properly. Of course we cannot give you a full introduction of pgp here. We will only mention the steps you have to do to get pgp going. For details you should have a look at the excellent pgp documentation.

It is certainly a good idea to study this documentation as well as an introduction into public key cryptography (e.g. out of the pgp 6.5.x package). There you can learn a lot about the basic concepts, which will help you to understand what is going on. As well, many security related issues you should know about are discussed there.

Now let's start.

## 3.7.1. Preconditions

KMail expects that your PGP binary is called pgp. In case of GnuPG, it expects the binary to be called gpg. If that's not the case for you, just make a symlink.

If you haven't done so, you have to generate a key pair (secret and public key) for your identity. You must do this at the command line (use `pgp `-kg``). KMail has no internal support for pgp's key generation at this time. The identity (normally your name followed by your email address within brackets, such as `John Doe <john@example.com>`) and your passphrase are important for the co-operation between KMail and pgp.

## 3.7.2. PGP Related Settings in KMail

Open the KMail Configure dialog and go to the Security settings page. Type your identity into the PGP user identity entry field. There are also three options:

Keep passphrase in memory

  When this option is off, then KMail will ask for your passphrase each time you sign a message (before sending) or decrypting a message (sent to you). If you turn this option on, KMail will remember your passphrase from after your first successful input until you finish your KMail session. The passphrase is stored in memory and not written to the harddisk.

  | Note that a user with enough privileges (e.g. root) might be able to catch your passphrase even from the computer's memory.

Always encrypt to self

  If this option is off and you want send an encrypted message to somebody, then you can't read this message any longer after you have composed and encrypted it. Turn this option on to keep sent encrypted messages readable for you too.

Show ciphered text after composing

  This will show you the result of encrypting and signing before the message gets sent. This way you can still cancel sending if encrypting failed. It is strongly recommended to use this option.

Encryption tool

  Here you can choose if you want to use GnuPG or PGP. Of course the program you select has to be installed on your system. It is also important to select the correct version.

On the Composer tab you can also check the Automatically sign messages using PGP option. This means that all your messages will be signed before being sent. (So you don't have to set the signing for each mail manually.)

Now you are able to sign outgoing messages. To let people send encrypted messages to you and to let them verify your signature you must send them your public key. To send encrypted mails to other people or to verify their signed messages you will need their public keys. You can store your public key(s) on a public PGP key server such as http://www.cam.ac.uk.pgp.net/pgpnet/.

## 3.7.3. Sign your Messages

You compose your message as usual in the Composer window of KMail. Before you send the message, check the button with the underlining icon on it in the toolbar of the composer window. Then, you can send the message. To sign it, KMail needs to know your pgp passphrase. If you didn't select Keep passphrase in memory in the Security settings tab, KMail will ask you for it. On the other hand, if you have already given the phrase to KMail, it will sign the message without any further prompt.

## 3.7.4. Send your Public Key

Prepare a message to the person you want to send your public key to. Then choose in the Composer window's menu Attach->Attach My Public Key. This will attach your public key to the mail. Now you can send the mail.

Remember that it's not safe at all if you sign the message to make sure that the receiver will get the correct key. There can be a man-in-the-middle attack, as somebody can change the key and sign the message with that other key. That's why the recipient should verify the attached key by checking the key's fingerprint against the one he got in a secure way from you. Have a look at the pgp documentation for further details.

## 3.7.5. You got an encrypted Message

All you have to do is to select the message in KMail. You will be prompted for your passphrase. Then KMail will try to decrypt the message and show you the plain text if the message had been encrypted with your public key. (If not, then you won't be able to read it.) KMail stores the messages encrypted, so nobody can read these messages without knowing your passphrase.

## 3.7.6. Receiving a Public Key

You can get a public key as an attachment or simply by ftp or floppy. Before you can use this key to encrypt a message to the owner of the key, you should verify the key (check its fingerprint or look for trusted signatures). Then you can add this key to your public keyring by typing `pgp `-ka` `filename`` at the command line. If the key is not certified with a trusted signature, you can't use it with KMail to encrypt messages unless you have signed that key (use `pgp `-ks` `identity of the key``).

## 3.7.7. Use Public Keys of other People - Encrypt your Messages

To send an encrypted message to somebody of whom you have a public key, you simply create the message in the composer window. Before you send the message, check the button with the lock symbol in the toolbar of the composer window. Then send the message.

If KMail can't find a key for any of the recipients, it will display a list containing all available keys. You can choose the appropriate key out of the list (or cancel the action). KMail might also inform you about errors throughout the encryption process.

As mentioned above, you won't be able to read your own encrypted sent mails if you don't check Always encrypt to self in the setting's Security tab.

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