Difference between revisions of "GnuPG"
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* Generate an ASCII version of your public key (e.g. to distribute it by e-mail):
* Generate an ASCII version of your public key (e.g. to distribute it by e-mail):
Revision as of 20:45, 22 November 2013
GnuPG can be used to sign and encrypt files or mails.
- 1 Installation
- 2 Environment Variables
- 3 Configuration file
- 4 Basic keys management
- 5 Basic usage
- 6 gpg-agent
- 7 Keysigning Parties
- 8 Smartcards
- 9 Troubleshooting
- 10 See also
GnuPGP uses the directory pointed to by
$GNUPGHOME to store all of its configuration files. By default
$GNUPGHOME isn't set and your
$HOME is used instead, thus you will find a
~/.gnupg directory right after the install. You may change this default setting by putting this line in one of your regular startup files
~/.gnupg/gpg.conf. If you want to change the default location, either run gpg this way
$ gpg --homedir path/to/file or use
Append in this file any long options you want. Do not write the two dashes, but simply the name of the option and required arguments. You will find a skeleton file
Following is a basic configuration file:
default-key name # useful in case you manage several keys and want to set a default one keyring file # will add file to the current list of keyrings trustdb-name file # use file instead of the default trustdb homedir dir # set the name of the gnupg home dir to dir instead of ~/.gnupg display-charset utf-8 # bypass all translation and assume that the OS uses native UTF-8 encoding keyserver name # use name as your keyserver no-greeting # suppress the initial copyright message armor # create ASCII armored output. Default is binary OpenPGP format
Basic keys management
- Set stronger algorithms to be used first:
# printf "\npersonal-digest-preferences SHA512\ncert-digest-algo SHA512\ndefault-preference-list SHA512 SHA384 SHA256 SHA224 AES256 AES192 AES CAST5 ZLIB BZIP2 ZIP Uncompressed" >> ~/.gnupg/gpg.conf
- Generate a private key by typing in a terminal:
# gpg --gen-key
You will be asked several questions. In general, most users will want both a RSA (sign only) and a RSA (encrypt only) key. It is advised t use a keysize of 4096 bits (default is 2048).
While having an expiration date for subkeys isn't technically necessary, it is considered good practice. A period of a year is generally good enough for the average user. This way even if you lose access to your keyring, it will allow others to know that it is no longer valid.
Manage your key
gpg --edit-key key ID or
gpg --edit-key User_name_uid command will present a menu which enables you to do most of your key management related tasks. Following is an example to set your expiration date:
$ gpg --edit-key User_name_uid > key number > expire yyyy-mm-dd > save > quit
Some useful commands:
> passwd # change the passphrase > clean # compact any user ID that is no longer usable (e.g revoked or expired) > revkey # revoke a key > addkey # add a subkey to this key
- Generate an ASCII version of your public key (e.g. to distribute it by e-mail):
$ gpg --armor --output public.key --export 'Your Name'
- Register your key with a public PGP key server, so that others can retrieve your key without having to contact you directly:
$ gpg --keyserver pgp.mit.edu --send-keys Key Id
- Sign and encrypt for user Bob
$ gpg se -r Bob file
If you have set your subkeys to expire after a set time, you will have to create new ones. Do this a few weeks in advanced to allow others to update their keyring.
- Create new subkey (repeat for both signing and encrypting key)
# gpg --edit-key 'Your Name' # addkey
And answer the following questions it asks (see previous section for suggested settings).
- Save changes
- Update it to a keyserver.
# gpg --keyserver pgp.mit.edu --send-keys Key Id
- Import a public key to your public key ring:
# gpg --import public.key
- Import a private key to your secret key ring:
# gpg --import private.key
- Keys in your public key ring:
# gpg --list-keys
- Keys in your secret key ring:
# gpg --list-secret-keys
You can use gnupg to encrypt your sensitive documents, but only individual files at a time.
For example, to decrypt a file, use:
# gpg -d secret.tar.gpg
You'll be prompted to enter your passphrase.
If you want to encrypt directories or a whole file-system you should consider using TrueCrypt, though you can always tarball various files and then encrypt them.
Gpg-agent is mostly used as daemon to request and cache the password for the keychain. This is useful if GnuPG is used from an external program like a mail client. It can be activated by adding following line in
This tells GnuPG to use the agent whenever it needs the password. However, the agent needs to run already. To autostart it, create the following file and make it executable, and remember to change the envfile path if you changed your $GNUPGHOME:
if [ $EUID -ne 0 ] ; then envfile="$HOME/.gnupg/gpg-agent.env" if [[ -e "$envfile" ]] && kill -0 $(grep GPG_AGENT_INFO "$envfile" | cut -d: -f 2) 2>/dev/null; then eval "$(cat "$envfile")" else eval "$(gpg-agent --daemon --enable-ssh-support --write-env-file "$envfile")" fi export GPG_AGENT_INFO # the env file does not contain the export statement export SSH_AUTH_SOCK # enable gpg-agent for ssh fi
If you don't want gpg-agent to autostart for all users or just want to keep user daemons in the users own configuration files you can add the following entry to your
eval $(gpg-agent --daemon) &
Log out of your Xsession and log back in. Check if
gpg-agent is activated
# pgrep agent
Finally, the agent needs to know how to ask the user for the password. This can be set in
The default uses a gtk dialog. To change it to ncurses or qt, set the following in the above file
For more options see
man gpg-agent and
To allow users to validate keys on the keyservers and in their keyrings (i.e. make sure they are from whom they claim to be), PGP/GPG uses a so-called "Web of Trust". To build this Web of Trust, many hacker events include keysigning parties.
For an easier process of signing keys and sending signatures to the owners after a keysigning party, you can use the tool 'caff'. It can be installed from the AUR with the packageAUR or bundled together with other useful tools in the package AUR. Either way, there will be a lot of dependencies installing from the AUR. Alternatively you can install them with
cpanm Any:Moose cpanm GnuPG::Interface
GnuPG uses scdaemon as an interface to your smartcard reader, please refer to
scdaemon man page for details.
GnuPG only setups
If you do not plan to use other cards but those based on GnuPG, you should check the
reader-port parameter in
~/.gnupg/scdaemon.conf. The value '0' refers to the first available serial port reader and a value of '32768' (default) refers to the first USB reader.
GnuPG together with OpenSC
If you are using any smartcard with an opensc driver (e.g.: ID cards from some countries) you should pay some attention to GnuPG configuration. Out of the box you might receive a message like this when using
gpg: selecting openpgp failed: ec=6.108
By default, scdaemon will try to connect directly to the device. This connection will fail if the reader is being used by another process. For example: the pcscd daemon used by OpenSC. To cope with this situation we should use the same underlying driver as opensc so they can work well together.
In order to point scdaemon to use pcscd you should remove
~/gnupg/scdaemon.conf, specify the location to libpcsclite.so library and disable ccid so we make sure that we use pcscd.
pcsc-driver /usr/lib/libpcsclite.so card-timeout 5 disable-ccid
man scdaemon if you do not use OpenSC.
pinentry, you must have the proper permisions of the terminal device (e.g.
/dev/tty1) in use. However, with
sudo), the ownership stays with the original user, not the new one. This means that pinentry will fail, even as root. The fix is to change the permissions of the device at some point before the use of pinentry (i.e. using gpg with an agent). If doing gpg as root, simply change the ownership to root right before using gpg
chown root /dev/ttyN # where N is the current tty
and then change it back after using gpg the first time. The equivalent is likely to be true with
Agent complains end of file
The default pinentry program is pinentry-gtk-2, which needs a DBus session bus to run properly. See General Troubleshooting#Session permissions for details.
Alternatively you can use the qt pinentry.
# ln -sf /usr/bin/pinentry-qt4 /usr/bin/pinentry