Introducción a GnuPrivacyGuard

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Introducción

GnuPG utiliza cifrado de chave pública para garantizar que os usuarios podan comunicarse de xeito seguro. Nun sistema de chave pública, cada usuario ten unha parella de chaves consistente nunha chave privada e unha chave pública. A chave privada do usuario se manten en segredo, únicamente o seu propietario terá acceso a ela. A chave pública é de acceso público: calqueira que queira comunicarse pode acceder a ela.

GnuPG, GPG, PGP e OpenPGP

Os térmos "OpenPGP", "PGP", and "GnuPG / GPG" se utilizan comúnmente como si foran o mesmo. Pero son lixeiramente distintos:

OpenPGP
é unha proposición de estándar, sin embargo, é de uso común.
PGP e GnuPG
Son programas que implementan o estándar OpenPGP.
PGP
Son as siglas de Pretty Good Privacy, un programa que proporciona privacidade e autenticación mediante cifrado.
GnuPG
Son as siglas de Gnu Privacy Guard, outro programa que tamén proporciona privacidade e autenticación mediante cifrado.

Xerando unha Chave Privada OpenPGP

O soporte de OpenPGP nos sistemas basados en Debian está no paquete gnupg.

Existen varias aplicacións que proporcionan unha interface gráfica para GnuPG:

  • Enigmail, un plugin de OpenPGP para Mozilla Thunderbird.
  • GNU Privacy Assistant unha interface gráfica para GnuPG (GNU Privacy Guard).
  • Seahorse é unha aplicación Gnome para manexar chaves de cifrado e contrasianis, integrándose con nautilus, gedit e outras aplicacións de Gnome.
  • KGPG é un interfaz simple de KDE para GPG.
  • Kleopatra é outro interfaz de KDE para GPG integrado coa suite de información persoal KDE PIM

Todas estas aplicacións permiten a xeración e xestión de chaves OpenPGP.

Utilizando GnuPG para xerar a chave privada

Podemos xerar nosa chave privada mediante a orde: 

gpg --gen-key

Aparecerá unha pantalla similar á seguinte 

Please select what kind of key you want:
  (1) RSA and RSA (default)
  (2) DSA and Elgamal
  (3) DSA (sign only)
  (4) RSA (sign only)

Elexindo a opción (1) poderemos firmar e cifrar mensaxes. A continuación nos preguntará polo tamaño de chave. O valor de 2048 que toma por defecto é unha boa elección.

O periodo de validez da chave toma por defecto o valor de validez perpetua. Si eleximos esta opción, debemos revocar a chave cando xa non a precisemos.

A pantalla seguinte nos solicitará a información necesaria para construír a chave: 

 You need a user ID to identify your key; the software constructs the user ID
 from the Real Name, Comment and Email Address in this form:
   "Heinrich Heine (Der Dichter) <heinrichh@duesseldorf.de>"

 Real name: Nome do Usuario
 Email address: direcciondousuario@dominio.net
 Comment: Comentario
 You selected this USER-ID:
     "Nome do Usuario (Comentario) <direcciondousuario@dominio.net>"

Debemos asegurarnos que o nome da chave (Real name) coincide co nome real, a poder ser tal e como aparece nas identificacións oficiais como o DNI. É posible engadir máis direccións de correo posteriormente.

No momento de crear a chave, se preguntará pola password de protección. O sistema combinará información aleatoria do sistema coa password para xerar a chave privada de usuario.

Boxinfo info.png
Si se olvida a password da chave privada, ésta se volverá inútil. Debemos ter especial coidado en non olvidala

Unha vez xerada a chave privada observaremos unha pantalla similar á seguinte: 

 gpg: key D8FC66D2 marked as ultimately trusted
 public and secret key created and signed.

 pub   1024D/D8FC66D2 2005-09-08
       Key fingerprint = 95BD 8377 2644 DD4F 28B5  2C37 0F6E 4CA6 D8FC 66D2
 uid                  Nome do Usuario (Comentario) <direcciondousuario@dominio.net>
 sub   2048g/389AA63E 2005-09-08

O KEY-ID da chave xerada será a que se observa despois de pub 1024D/, neste caso D8FC66D2. Si queremos que as aplicacións que utilizan GPG fagan uso automáticamente desta chave podemos exportar o seu ID na variable de entorno GPGKEY incluíndo en .bashrc export GPGKEY=D8FC66D2.

Si queremos que este cambio faga efecto antes do seguinte inicio de sesión, podemos facer: 

  killall -q gpg-agent
  eval $(gpg-agent --daemon)
  source ~/.bashrc

Cifrado

Si no momento de crear a chave privada, xeramos unha chave únicamente de firma como RSA (sign only) podemos engadirlle capacidade de cifrado: 

gpg --cert-digest-algo=SHA256 --edit-key $GPGKEY

Sendo $GPGKEY o KEY-ID da chave. Veremos unha pantalla co seguinte: 

 Secret key is available.
 pub   2048R/D8FC66D2  created: 2005-09-08  expires: never       usage: SC  
                    trust: ultimate      validity: ultimate
 [ultimate] (1). Nome do Usuario (Comentario) <direcciondousuario@dominio.net>
 Command>

Introduciremos o comando addkey, se nos solicitará a password da nosa chave privada e veremos algo como esto: 

 Please select what kind of key you want:
   (2) DSA (sign only)
   (4) Elgamal (encrypt only)
   (5) RSA (sign only)
   (6) RSA (encrypt only)

A mellor opción á a 6 cun tamaño de chave de 2048. Tamén se preguntará, de modo similar á creación da chave privada, polo tempo de validez. Veremos unha pantalla similar a seguinte: 

 pub   2048R/D8FC66D2  created: 2005-09-08  expires: never       usage: SC  
                    trust: ultimate      validity: ultimate
 sub   2048R/389AA63E created: 2005-09-08  expires: never       usage: E   
 [ultimate] (1). Nome do Usuario (Comentario) <direcciondousuario@dominio.net>
 Command>

e Introduciremos os comandos save e quit.

Creación da Chave de Revocación

Si a chave privada se vera comprometida (alguén consigue acceso a ela) ou xa non queremos que continúe sendo válida, necesitaremos revocar a súa validez. Para eso necesitaremos un certificado de revocación. Se recomenda crear un certificado de revocación no momento de xerar a chave privada e mantelo en lugar seguro. Podemos xerar un certificado de revocación mediante: 

gpg --output revoke.asc --gen-revoke $GPGKEY

Este certificado pode imprimirse ou almacenarse nun ficheiro.

Boxinfo info.png
Calqueira que teña acceso ao certificado de revocación pode cancelar a validez da chave privada

Creación dunha versión ASCII da chave pública

Existen varios sitios que permiten pegar a versión ASCII dunha chave pública para importala. E tamén de uso común incluír a chave pública como parte dunha mensaxe de e-mail en forma de un attach ASCII. Para obter a versión ASCII da nosa chave pública utilizaremos o seguinte comando: 

gpg --output mykey.asc --export -a $GPGKEY

Subir a chave pública a un servidor público de chaves

Si queremos que calqueira poda acceder a nosa chave pública cando a necesite, a mellor opción e o uso dun servidor de chave pública. Existen numerosos servidores públicos de chaves PGP e a maior parte deles ofrecen unha interface web na que podemos pegar a versión ASCII da nosa chave. Unha vez que subamos a chave a un servidor de chaves, se propagará a outros de xeito que a maior parte dos servidores terán unha versión da mesma. Se pode acelerar a propagación enviando a chave a varios servidores.

Por exemplo, para enviar a nosa chave ao servidor de chaves público de Ubuntu, faríamos: 

gpg --send-keys --keyserver keyserver.ubuntu.com $GPGKEY

Ou ben pegando a versión ASCII da chave en http://keyserver.ubuntu.com

Utilizando OpenPGP co E-mail

As chaves OpenPGP poden utilizarse para firmar, cifrar e descifrar mensaxes de e-mail, ofrecendo gran seguridade. Moitos clientes de correo electrónico ofrecen soporte de cifrado/descifrado e firma/verificación mediante OpenPGP.

Validation on Launchpad

You need to tell Launchpad about your OpenPGP key(s) to be able to sign the Ubuntu Code of Conduct (and thus become an Ubuntero) and to build packages using HCT.

OpenPGP keys and Launchpad

* Visit the OpenPGP Keys page once logged into Launchpad.  Paste your key fingerprint into the textbox:{{{

gpg --fingerprint}}} 

 * Modelo:Attachment:IconsPage/example.png The key fingerprint would be something like: {{{

95BD 8377 2644 DD4F 28B5 2C37 0F6E 4CA6 D8FC 66D2}}} 

 Launchpad will send you an email which you will have to decrypt.  You can save the text to a file:

 (Sample message- make sure not to alter format)
 {{{

BEGIN PGP MESSAGE-----

Version: GnuPG v1.4.3 (GNU/Linux)

hQIOA0THhKozD+K5EAf9F3PcOL2iU6onH2YsvB6IKDXNxbK0NBVy6ppxcNq8hoTe cuHvzWLFfh1ehhSNe1V6xpuFnt5sJoeA4qEEOxez3HmY80tKIKMPLyhC/8JiSIW9 fwuxj4C0F6pdyrpvGbQAzfPEFk/P1AtIHXm4WLXduhBT7YEpmUk/I4A/KlSrKoiP J5vBtbroUyp2jvIhDUmY7ToU+ifrDe3+VP1ZzSEJzOOXec9oPbcbvf5NptXA7Hbp S0ElBAcLjKpAu7VKotCwFZIsVXDHT/mxf2qm88bGIrlXS5uTzvmyhQps1KmyNiCz I0i5kSVvHZWyVZ+8FrROLqYAqqnEIMg9hUnbFAervgf/YiYs0xxWLYf9e14eoMZA ranGT72q/JHmBNBYenOijaquFNi1TH5J8Udtt2RfdyRUlmGilxRvtIYL8gpnuNpS +GHOoBWUN2f4nawaDeqgrf6Nt3qQWWLO4iJPgieejFP2FP6zkLme1t7dXo+z1ary EZuxSLtKIWkOFEZ8Gcn02hBgOhJZucnkF6BmVW9dr1C4QEAmGM631uqfsp5PapAn yjHbEU1L2R9i7vPtJNRr6ubFLWg1Yhfv63ByxSx/WQHMMqlrbL+moXBGED3L2hM8 7FP9eapBRgmS+Bda9ArcGMUElTOkWoUYIOPyLOYmo15LvbxHOVaXjn7+fDgr2S1J R9LArwHycmdKKelRww+ZvylHIfq8xy10atRQIYawchh9A1myXD1TlWbrrIkodQJF iEpO2i1LKvqwZHOx3szT4hF+44tNFzQIL1j+zF5Hrt2WOTnS5WXGgGRtfEd8F7fN khQZOAdhwrnlY+yknruC8Y8Jm8vM57+KnPgBfvxuxzLX1XFTfTZCHXeUmwwu3mga m+6WzckeBGBDHKK6GqwFoOAykTwjyqOZaty7DPHeoINc0tLMVr9Ks64DScf8bgh4 MkNonA0YhMQbkmwRc33APw441+/iLw5gqndQdX44kKqC71dG6LqanAOjD29Xj3JV ZBsjg95Jrx7Sx+i/V0PUeaU9QjCT0Q1jEy1Bcs8NYtTJnpG+4oHYJ0pyiGxIquQH V9E+hW6Qehx5DbsIXEvfeaBBHOfAHHOhUH14WK4bsJWm8wZ50XiYBZrNFOqzsm13 2STcY4VIoJp3Uw2qNyvZXQUhpndlfgQGO14CMSadzDn6Vts= =hTe6

END PGP MESSAGE-----}}} 

* Now run:{{{

gpg --decrypt file.txt}}} 

 * You will need to enter your passphrase.

* The message will be displayed along with the link you must follow to confirm your key in Launchpad.

* Follow the link, enter your Launchpad password as asked, and you are done!

Validating using Firefox and FireGPG

* If you are on gmail, using the FireGPG addon, simply scroll down and click "decrypt this mail". You will now see the decrypted message with a link and a token. Copy that URL:

{{{https://launchpad.net/token/somealphanumerictoken}}}

 * Follow the link and click on "Confirm". Please note that validation does take some time. If you run into an internal 500 server, simply try again with the same token.

* A confirming page should appear once the validation is successfully completed.

Signing Data

Signing data is helpful in verifying if the data from a person is indeed from that person. A typical scenario is described below.

Launchpad Key Signing

When you've set up GnuPG and have a key in the strong set, it is time to sign the Ubuntu Code Of Conduct if you want to become an Ubuntu member or Ubuntero. Signing is done in 3 easy steps: 

1. Download the code of conduct from https://launchpad.net/codeofconduct/2.0/+download.
1. Run the command {{{

gpg --clearsign UbuntuCodeofConduct-2.0.txt}}} 

1. Upload the contents of Ubuntu``Codeof``Conduct-2.0.txt.asc on https://launchpad.net/codeofconduct/2.0/+sign

Getting your key signed

The whole point of all this is to create a web of trust. By signing someone's public key, you state that you have checked that the person that uses a certain keypair, is who he says he is and really is in control of the private key. This way a complete network of people who trust each other can be created. This network is called the Strongly connected set. Information about it can be found at http://pgp.cs.uu.nl/

In summary, 

1. Locate someone that lives near you and can meet with you to verify your ID. Sites like http://www.biglumber.com/ are useful for this purpose
1. Arrange for a meeting. Bring at least one ID with photo and printed fingerprint of your OpenPGP key, ask the same from the person you will be meeting with.
1. Print copies of your public key
 * get the last eight digits of your fingerprint: 0995 ECD6 3843 CBB3 C050  28CA E103 6EED 0123 4567
 * terminal: gpg --fingerprint 01234567 >> key.txt
 * print the resulting key.txt file and bring as many copies to the meeting as you expect to have people sign
1. Meet, verify your IDs and exchange OpenPGP key fingerprints
1. Sign the key of the person you've just met. Send him/her the key you've just signed.
1. Update your keys on the keyserver, the signature you've just created will be uploaded.

Keysigning Guidelines

Since a signature means that you checked and verified that a certain public key belongs to a certain person who is in control of the accompanying private key, you need to follow these guidelines when signing peoples keys:

During the Event

1. Keysigning is always done after meeting in person
1. During this meeting you hand each other your OpenPGP key fingerprint and at least one government issued ID with a photograph. These key fingerprints are usually distributed as key fingerprint slips, created by a script such as gpg-key2ps (package: signing-party)
1. You check whether the name on the key corresponds with the name on the ID and whether the person in front of you is indeed who he says he is.

After the Event

You now have the printed public key information from the other participants.

Example key IDs for the other participants will be E4758D1D, C27659A2, and 09026E7B. Replace these IDs with the key IDs you received from the other participants. 

1. retrieve the keys:
 * gpg --recv-keys E4758D1D C27659A2 09026E7B
1. sign the keys:
 * gpg --sign-key E4758D1D
 * gpg --sign-key C27659A2
 * gpg --sign-key 09026E7B
1. export the keys
 * gpg --armor --export E4758D1D --output E4758D1D.signed-by.01234567.asc
 * gpg --armor --export C27659A2 --output C27659A2.signed-by.01234567.asc
 * gpg --armor --export 09026E7B --output 09026E7B.signed-by.01234567.asc
1. Email the key users (use the email address that was part of the key's user ID) and attach the corresponding signature file - or  - send their signed key to the key server:
 * gpg --send-keys --keyserver keyserver.ubuntu.com E4758D1D
1. Once you receive your signed key import them to your keyring:
 * gpg --import 01234567.signed-by.E4758D1D.asc
 * gpg --import 01234567.signed-by.C27659A2.asc
 * gpg --import 01234567.signed-by.09026E7B.asc
1. You should see your keys:
 * gpg --list-sigs 01234567
1. Send your keys to the keyserver:
 * gpg --send-keys 01234567

Congrats you have now entered a web of trust or enlarged an existing one.

Backing up and restoring your key pair

Why should you back up your key pair? If you lose your key pair: 

* Any files encrypted with the lost key pair will be unrecoverable. 
* You will not be able to decrypt mails sent to you.
 * Decrypting emails sent to you requires your private key, this key is not stored on the keyservers.

If you lose your keypair you should revoke your key. This cannot be done without a revocation key.


Backing up your public key

* List your public keys:{{{

gpg --list-keys }}} 

* Look for the line that starts something like "pub 1024D/".  The part after the 1024D is the key_id.  To export the key:{{{

gpg -ao _something_-public.key --export key_id }}}

Backing up your private key

* List your secret keys:{{{

gpg --list-secret-keys }}} 

* Look for the line that starts something like "sec 1024D/".  The part after the 1024D is the key_id.  To export the secret key:{{{

gpg -ao _something_-private.key --export-secret-keys key_id }}}

Restoring your keys

* To restore your keys - copy the two files created above to the machine and type: {{{

gpg --import _something_-public.key gpg --import _something_-private.key }}}

Make sure you protect these files!

Revoking a keypair

In the event your keys are lost or compromised, you should revoke your keypair. This tells other users that your key is no longer reliable. ||Modelo:Attachment:IconsPage/warning.png For security purposes, there is no mechanism in place to revoke a key without a revocation key. As much as you might want to revoke a key, the revocation key prevents malicious revocations. Guard your revocation key with the same care you would use for your private key. || 

* To revoke your key you need to first create a revocation key with the command:

{{{ gpg --gen-revoke }}} 

 * Import your revocation key, which would be stored to the file revoke.asc by default:

{{{ gpg --import revoke.asc }}} 

 * Upload the revocation key to your keyserver of choice, in the following example the key will be send to ubuntus keyserver:

{{{ gpg --keyserver keyserver.ubuntu.com --send-key 6382285E }}}

Un-revoking a keypair

If you unintentionally revoke a key, or find that your key has in fact not been lost or compromised, it is possible to un-revoke your key. First and foremost, ensure that you do not distribute the key, or send it to the keyserver. 

 * Export the key

{{{ gpg --export <key> > key.gpg }}} 

 * Split the key into multiple parts. This breaks the key down into multiple parts.

{{{ gpgsplit key.gpg }}} 

 * Find which file contains the revocation key. In most cases, it is 000002-002.sig, however you should make sure by using the following. If the sigclass is 0x20, you have the right file. Delete it.

{{{ gpg --list-packets 000002-002.sig }}} 

 * Put the key back together

{{{ cat 0000* > fixedkey.gpg }}} 

 * Remove the old key

{{{ gpg --expert --delete-key <key> }}} 

 * Import the new key

{{{ gpg --import fixedkey.gpg }}}

GPG 2.0

||Modelo:Attachment:IconsPage/info.png GPG 2.0 is not installed as a default application on Ubuntu.|| GPG 2.0 is the new kid on the block. GPG 2.0 is aimed or done for the desktops rather than embedded or server applications. 

* GnuPG2 is available in the "Main" repository since Intrepid, or in the "Universe" repository in earlier releases.
 * If you want to use gnupg2 with the firegpg firefox extension, you need to install gnupg2 first.   
* More information of GnuPG2 can be found [[1]] 
* If you are going to use gpg2 for the same purposes as outlined above then you just need to add `2` to the gpg command.
Modelo:Attachment:IconsPage/example.png {{{

gpg2 --gen-key }}}

Tips and Tricks

* Add your key to ~/.bashrc by adding a line similiar to {{{export GPGKEY=YOUR-KEY-ID}}}
* gnupg-agent and pinentry-gtk2 are packages that facilitate not having to enter the password for your key every time you want to use it. Open the file {{{~/.gnupg/gpg.conf}}} in your favorite editor. Browse through it and change what you like. A few useful things to change are:
   * keyserver-options auto-key-retrieve
   * use-agent (the Ubuntu default for Gutsy and later releases.)

The former makes gpg automatically retrieve gpg keys when verifying signatures. The latter makes you use gpg-agent, which is very useful if you use gpg a lot but don't like typing your password all the time. It is also required for some programs (such a Kmail) to sign or encrypt messages). Gnupg-agent and pinentry are in Main for Gutsy and automatically installed/configured in Kubuntu. If you are upgrading from Ubuntu 7.04 (Fiesty), the file ~/.gnupg/gpg.conf may have failed to be created by default in your home directory due to a bug in the gnupg package. In that case, GPG agent integration will not be enabled by default. If you have not created your own gpg.conf, you can correct this issue by running {{{cp /usr/share/gnupg/options.skel ~/.gnupg/gpg.conf}}}. If you do have a gpg.conf and are affected by this issue, that command would overwrite it with Ubuntu's default options and wipe any customizations you have made; you can still correct the issue by running {{{echo use-agent >> ~/.gnupg/gpg.conf}}} instead.

Now create the file ~/.gnupg/gpg-agent.conf with the following content: {{{ pinentry-program /usr/bin/pinentry-gtk-2 default-cache-ttl 86400 max-cache-ttl 86400}}}

This will make gpg-agent use pinentry-gtk2 and it will remember your password for 24 hours (please consider the security implications for doing this - anyone gaining access to your computer for 24 hours would then be able to sign anything with your key). For Kubuntu, use pinentry-qt4 instead.

  • Changing your password. If you wish to change the password of a key, you can use
{{{

gpg --edit-key userid }}} (the 'real name' part of the userid suffices). Choose {{{ passwd }}} in the menu and enter the new password twice. You can leave the menu using {{{ quit }}}.


Este documento é unha traducción e adaptación da documentación de Ubuntu con licencia Creative Commons

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