added openpgp and linked it

wiki/linux/gpg.md

@@ -1,7 +1,7 @@
 # GPG
 
 [GNU Privacy Guard](https://gnupg.org/) - short GnuPG or just GPG - is a free and open-source
-implementation of OpenPGP from [RFC 4880](https://datatracker.ietf.org/doc/html/rfc4880).
+implementation of [OpenPGP](/wiki/openpgp.md).
 It is used to savely encrypt and decrypt messages or files using assymetric encryption.
 
 ## Setup
@@ -13,6 +13,15 @@ Sometimes it is also called `gnupg2`.
 
 This section addresses the usage of the Open GPG.
 
+### List or Find a Key
+
+To find a key use the following command.
+`<query>` is a search string and is optional.
+
+```sh
+gpg --list-keys <query>
+```
+
 ### Generating a Key Pair
 
 A fast way to generate a key pair is by running the following command.
@@ -104,6 +113,27 @@ gpg --recv-key <id>
 gpg --lsign <id>
 ```
 
+### Managing Multiple Users and E-Mails of an Existing Secret Key
+
+A secret key can have more than one e-mail assigned to it.
+After generating the key however only a single user is added by default.
+
+To add another one use the following command where `<key-id>` is the id of the key to add the
+e-mail to.
+
+```sh 
+gpg --edit-key <key-id>
+```
+
+Afterwards a console will open.
+Using `adduid` another user can be added by following the on-screen instructions.
+Afterwards `save` will save the progress and exit from the console.
+
+To delete an existing user and e-mail also open the edit-console.
+Then list the existing users using the command `uid` and select the user id of the key to delete
+with `uid <id>` where `<id>` is the key to delete.
+Then delete it with `deluid` and save with `save`.
+
 ## Troubleshooting 
 
 This section will focus on errors and the fixing of errors of GPG.

wiki/openpgp.md

@@ -0,0 +1,11 @@
+# OpenPGP
+
+[OpenPGP](https://www.openpgp.org/) is the most widely used encryption standard proposed in from
+[RFC 4880](https://datatracker.ietf.org/doc/html/rfc4880).
+
+## Setup
+
+There are different implementations of OpenPGP.
+Many [Linux](/wiki/linux.md) [package managers](/wiki/linux/package_manager.md) 
+package the implementation called [Gnu Privacy Guard](/wiki/linux/gpg.md) in the `gnupg` or
+sometimes also `gpg` or `gpg2` package.

wiki/thunderbird.md

@@ -7,7 +7,25 @@ numerous e-mail addresses, calendars, todos and contacts.
 
 The following section addresses different uses and add-ons of Thunderbird.
 
-### Changing the (dark/light) Theme
+### Use PGP Key for Encryption, Decryption and Signing
+
+Thunderbird can use [OpenPGP](/wiki/openpgp.md) to sign, encrypt or decrypt mails.
+To add this navigate to the `Account Settings` under `Edit` and then select the mail to add the PGP
+key to and `End-to-End Encryption`.
+There keys can be added by selecting `Add Keys...` and afterwards the private key can be selected
+for encryption, decryption and signing.
+This however is only possible if the key is issued to the same e-mail it should be added to.
+
+### Enable Spell Checking of a Specific Language
+
+Spell checking can be changed in the `Settings` from the `Edit` tab.
+The configuration can be done under `Composition` in the `Spelling` section.
+There are two checkboxes to specify when the spell checking should occur.
+And under `Languages:` various and also multiple languages can be checked.
+To add another language follow the link and navigate to the language to install.
+Then install only dictionary since the language pack is not needed.
+
+### Changing the (Dark/Light) Theme
 
 This section is based on a
 [superuser comment by blnks](https://superuser.com/questions/1757333/how-can-i-view-thunderbird-in-full-dark-mode).