Difference between revisions of "GnuPG"

From ArchWiki
Jump to: navigation, search
(Manage your key)
m (Fix minor formatting issue)
(4 intermediate revisions by 2 users not shown)
Line 7: Line 7:
  
 
==Environment Variables==
 
==Environment Variables==
{{ic|GnuPGP}} uses the directory pointed to by {{ic|$GNUPGHOME}} to store all of its configuration files. By default {{ic|$GNUPGHOME}} isn't set and your {{ic|$HOME}} is used instead, thus you will find a {{ic|~/.gnupg}} directory right after the install. You may change this default setting by putting this line in one of your regular [[Startup_files|startup files]]
+
* {{ic|$GNUPGHOME}} is used by {{ic|GnuPGP}} to point to the directory where all configuration files are stored. By default {{ic|$GNUPGHOME}} isn't set and your {{ic|$HOME}} is used instead, thus you will find a {{ic|~/.gnupg}} directory right after the install. You may change this default setting by putting this line in one of your regular [[Startup_files|startup files]]
 
  export GNUPGHOME="/path/to/gnupg/directory"
 
  export GNUPGHOME="/path/to/gnupg/directory"
 
{{Note| by default, the gnupg directory has a particular [[Permissions]] set to ''600''. Only the owner of the directory has permission to read and write (''r'',''w''). This is for security purposes and should not be changed. In case this directory or any file inside it does not follow this security measure, you will get warnings about unsafe file and home directory permissions.}}
 
{{Note| by default, the gnupg directory has a particular [[Permissions]] set to ''600''. Only the owner of the directory has permission to read and write (''r'',''w''). This is for security purposes and should not be changed. In case this directory or any file inside it does not follow this security measure, you will get warnings about unsafe file and home directory permissions.}}
 +
* {{ic|GPG_AGENT_INFO}} used to loacte the pgp-agent. Consists of 3 colon delimited fields:
 +
**1. path to Unix Domain Socket
 +
**2. PID of gpg-agent
 +
**3. protocol version set to 1
 +
E.g : {{ic|GPG_AGENT_INFO=/tmp/gpg-eFqmSC/S.gpg-agent:7795:1}}. When starting the gpg-agent, this variable is set to the correct value.
  
 
==Configuration file==
 
==Configuration file==
Line 64: Line 69:
 
* Sign and encrypt for user Bob
 
* Sign and encrypt for user Bob
 
  $ gpg se -r Bob ''file''
 
  $ gpg se -r Bob ''file''
 +
 +
* make a clear text signature
 +
$ gpg --clearsign ''file''
  
 
=== Rotating subkeys ===
 
=== Rotating subkeys ===
Line 128: Line 136:
 
         eval "$(gpg-agent --daemon --enable-ssh-support --write-env-file "$envfile")"
 
         eval "$(gpg-agent --daemon --enable-ssh-support --write-env-file "$envfile")"
 
     fi
 
     fi
export GPG_AGENT_INFO  # the env file does not contain the export statement
+
    export GPG_AGENT_INFO  # the env file does not contain the export statement
export SSH_AUTH_SOCK  # enable gpg-agent for ssh
+
    export SSH_AUTH_SOCK  # enable gpg-agent for ssh
 
fi
 
fi
 
</nowiki>}}
 
</nowiki>}}
Line 206: Line 214:
  
 
  # ln -sf /usr/bin/pinentry-qt4 /usr/bin/pinentry
 
  # ln -sf /usr/bin/pinentry-qt4 /usr/bin/pinentry
 +
 +
=== Configuration permissions ===
 +
 +
GnuPG needs the correct permissions on the ~/.gnupg folder and its contents to function correctly (KGpg have shown to not work on a default setup).
 +
 +
The ~/.gnupg folder needs drwxr-xr-x
 +
 +
It's contents all need -rw------- except for its folders which all needs drwx------ (x on folders make its contentfiles readable).
  
 
== See also ==
 
== See also ==
  
 
* [http://blog.sanctum.geek.nz/series/linux-crypto/ A more comprehensive gpg Tutorial]
 
* [http://blog.sanctum.geek.nz/series/linux-crypto/ A more comprehensive gpg Tutorial]

Revision as of 21:47, 2 December 2013

GnuPG can be used to sign and encrypt files or mails.

Installation

Install gnupg, available in the official repositories.

Environment Variables

  • $GNUPGHOME is used by GnuPGP to point to the directory where all configuration files are stored. 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
export GNUPGHOME="/path/to/gnupg/directory"
Note: by default, the gnupg directory has a particular Permissions set to 600. Only the owner of the directory has permission to read and write (r,w). This is for security purposes and should not be changed. In case this directory or any file inside it does not follow this security measure, you will get warnings about unsafe file and home directory permissions.
  • GPG_AGENT_INFO used to loacte the pgp-agent. Consists of 3 colon delimited fields:
    • 1. path to Unix Domain Socket
    • 2. PID of gpg-agent
    • 3. protocol version set to 1

E.g : GPG_AGENT_INFO=/tmp/gpg-eFqmSC/S.gpg-agent:7795:1. When starting the gpg-agent, this variable is set to the correct value.

Configuration file

Default is ~/.gnupg/gpg.conf. If you want to change the default location, either run gpg this way $ gpg --homedir path/to/file or use $GNUPGHOME variable.

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 usr/share/gnupg/gpg-conf.skel. Following is a basic configuration file:

~/.gnupg/gpg.conf
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

Create key

  • 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

  • Running the 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
  • make a clear text signature
$ gpg --clearsign file

Rotating subkeys

Warning: Never delete your expired or revoked subkeys unless you have a good reason. Doing so will cause you to lose the ability to decrypt files encrypted with the old subkey. Please only delete expired or revoked keys from other users to clean your keyring.

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
# save
  • Update it to a keyserver.
# gpg  --keyserver pgp.mit.edu --send-keys Key Id
Note: Revoking expired subkeys is unnecessary and arguably bad form. If you are constantly revoking keys, it may cause others to lack confidence in you.

Import key

  • 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

List keys

  • Keys in your public key ring:
# gpg --list-keys
  • Keys in your secret key ring:
# gpg --list-secret-keys

Basic usage

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.

Symmetric Encryption

gpg-agent

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 ~/.gnupg/gpg.conf:

use-agent

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:

/etc/profile.d/gpg-agent.sh
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 .xinitrc:

eval $(gpg-agent --daemon) &

Log out of your Xsession and log back in. Check if gpg-agent is activated

# pgrep agent

Pinentry

Finally, the agent needs to know how to ask the user for the password. This can be set in ~/.gnupg/gpg-agent.conf

The default uses a gtk dialog. To change it to ncurses or qt, set the following in the above file

pinentry-program /usr/bin/pinentry-curses

or

pinentry-program /usr/bin/pinentry-qt4

For more options see man gpg-agent and info pinentry.

Keysigning Parties

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.

The Zimmermann-Sassaman key-signing protocol is a way of making these very effective. Here you'll find a How-To-article.

Caff

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 package caff-svnAUR or bundled together with other useful tools in the package signing-party-svnAUR. 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 

To send the signatures to their owners you need a working MTA. If you don't have already one, install SSMTP.

Smartcards

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 --card-status

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 reader-port from ~/gnupg/scdaemon.conf, specify the location to libpcsclite.so library and disable ccid so we make sure that we use pcscd.

~/scdaemon.conf
pcsc-driver /usr/lib/libpcsclite.so 
card-timeout 5
disable-ccid

Please check man scdaemon if you do not use OpenSC.

Troubleshooting

Su

When using pinentry, you must have the proper permisions of the terminal device (e.g. /dev/tty1) in use. However, with su (or 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 /dev/pts/.

Note: being part of the group tty does not seem to alleviate the issue, at least as root. (Please confirm with non-superusers)

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

Configuration permissions

GnuPG needs the correct permissions on the ~/.gnupg folder and its contents to function correctly (KGpg have shown to not work on a default setup).

The ~/.gnupg folder needs drwxr-xr-x

It's contents all need -rw------- except for its folders which all needs drwx------ (x on folders make its contentfiles readable).

See also